environmental migration essay

The climate crisis, migration, and refugees

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John podesta john podesta founder and director - the center for american progress.

July 25, 2019

18 min read

The following is one of eight briefs commissioned for the 16th annual Brookings Blum Roundtable, “2020 and beyond: Maintaining the bipartisan narrative on US global development.”

On March 14, 2019, Tropical Cyclone Idai struck the southeast coast of Mozambique. The U.N. High Commissioner for Refugees reported that 1.85 million people needed assistance. 146,000 people were internally displaced, and Mozambique scrambled to house them in 155 temporary sites. 1 The cyclone and subsequent flooding damaged 100,000 homes, destroyed 1 million acres of crops, and demolished $1 billion worth of infrastructure. 2

One historic storm in one place over the course of one day. While Cyclone Idai was the worst storm in Mozambique’s history, the world is looking towards a future where these “unprecedented” storms are commonplace. This global challenge has and will continue to create a multitude of critical issues that the international community must confront, including:

Large-scale human migration due to resource scarcity, increased frequency of extreme weather events, and other factors, particularly in the developing countries in the earth’s low latitudinal band
Intensifying intra- and inter-state competition for food, water, and other resources, particularly in the Middle East and North Africa
Increased frequency and severity of disease outbreaks
Increased U.S. border stress due to the severe effects of climate change in parts of Central America

All of these challenges are serious, but the scope and scale of human migration due to climate change will test the limits of national and global governance as well as international cooperation.

The migration-climate nexus is real, but more scrutiny and action are required

In 2018, the World Bank estimated that three regions (Latin America, sub-Saharan Africa, and Southeast Asia) will generate 143 million more climate migrants by 2050. 3 In 2017, 68.5 million people were forcibly displaced, more than at any point in human history. While it is difficult to estimate, approximately one-third of these (22.5 million 4 to 24 million 5 people) were forced to move by “sudden onset” weather events—flooding, forest fires after droughts, and intensified storms. While the remaining two-thirds of displacements are the results of other humanitarian crises, it is becoming obvious that climate change is contributing to so-called slow onset events such as desertification, sea-level rise, ocean acidification, air pollution, rain pattern shifts and loss of biodiversity. 6 This deterioration will exacerbate many humanitarian crises and may lead to more people being on the move.

Multilateral institutions, development agencies, and international law must do far more to thoroughly examine the challenges of climate change (early efforts, like the World Bank’s 2010 World Development Report on climate change, 7 had little uptake at a time when few thought a climate crisis was around the corner). Moreover, neither a multilateral strategy nor a legal framework exist to account for climate change as a driver of migration. Whether in terms of limited access to clean water, food scarcity, agricultural degradation, or violent conflict, 8 climate change will intensify these challenges and be a significant push factor in human migration patterns.

To date, there are only a few cases where climate change is the sole factor prompting migration. The clearest examples are in the Pacific Islands. The sea level is rising at a rate of 12 millimeters per year in the western Pacific and has already submerged eight islands. Two more are on the brink of disappearing, prompting a wave of migration to larger countries. 9 10 By 2100, it is estimated that 48 islands overall will be lost to the rising ocean. 11 In 2015, the Teitota family applied for refugee status in New Zealand, fleeing the disappearing island nation of Kiribati. 12 Their case, the first request for refuge explicitly attributed climate change, made it to the High Court of New Zealand but was ultimately dismissed. Islands in the Federated States of Micronesia have drastically reduced in size, washed down to an uninhabitable state, had their fresh water contaminated by the inflow of seawater, and disappeared in the past decade. 13 Despite their extreme vulnerability, the relatively small population (2.3 million people spread across 11 countries 14 ) and remote location of the Pacific Islands means that they garner little international action, for all the attention they receive in the media.

Although there are few instances of climate change as the sole factor in migration, climate change is widely recognized as a contributing and exacerbating factor in migration and in conflict.

In South Asia, increasing temperatures, sea level rise, more frequent cyclones, flooding of river systems fed by melting glaciers, and other extreme weather events are exacerbating current internal and international migration patterns. Additionally, rapid economic growth and urbanization are accelerating and magnifying the impact and drivers of climate change—the demand for energy is expected to grow 66 percent by 2040. 15 Compounding this, many of the expanding urban areas are located in low-lying coastal areas, already threatened by sea level rise. 16 The confluence of these factors leads the World Bank to predict that the collective South Asian economy (Bangladesh, Bhutan, India, the Maldives, Nepal, and Sri Lanka) will lose 1.8 percent of its annual GDP due to climate change by 2050. 17 The New York Times reports that the living conditions of 800 million people could seriously diminish. 18 Diminishing living conditions on this scale and intensity will prompt mass migration—possibly at an unprecedented level.

Northwest Africa is facing rising sea levels, drought, and desertification. These conditions will only add to the already substantial number of seasonal migrants and put added strain on the country of origin, as well as on destination countries and the routes migrants travel. The destabilizing effects of climate change should be of great concern to all those who seek security and stability in the region. Climate and security experts often cite the impacts of the extreme drought in Syria that preceded the 2011 civil war. 19 The security community also highlights the connection between climate change and terrorism—for instance, the decline of agricultural and pastoral livelihoods has been linked to the effectiveness of financial recruiting strategies by al-Qaida. 20

The intersection of climate change and migration requires new, nimble, and comprehensive solutions to the multidimensional challenges it creates. Accordingly, the signatories to the 2015 Paris Agreement on climate change requested that the Warsaw International Mechanism for Loss and Damage Associated with Climate Change (WIM) develop recommendations for addressing people displaced by climate change. 21 Similarly, The Global Compact for Safe, Orderly, and Regular Migration (adopted by 164 countries—not including the U.S.—in Marrakech in December 2018) called on countries to make plans to prevent the need for climate-caused relocation and support those forced to relocate. 22 However, these agreements are neither legally binding nor sufficiently developed to support climate migrants—particularly migrants from South Asia, Central America, Northwest Africa, and the Horn of Africa.

Time to envision legal recourse for climate refugees

As gradually worsening climate patterns and, even more so, severe weather events, prompt an increase in human mobility, people who choose to move will do so with little legal protection. The current system of international law is not equipped to protect climate migrants, as there are no legally binding agreements obliging countries to support climate migrants.

While climate migrants who flee unbearable conditions resemble refugees, the legal protections afforded to refugees do not extend to them. In the aftermath of World War II, the United Nations established a system to protect civilians who had been forced from their home countries by political violence. Today, there are almost 20.4 million officially designated refugees under the protection of the United Nations High Commission for Refugees (UNHCR)—however, there is an additional group of 21.5 million people 23 who flee their homes as a result of sudden onset weather hazards every year. 24

The UNHCR has thus far refused to grant these people refugee status, instead designating them as “environmental migrants,” in large part because it lacks the resources to address their needs. But with no organized effort to supervise the migrant population, these desperate individuals go where they can, not necessarily where they should. As their numbers grow, it will become increasingly difficult for the international community to ignore this challenge. As severe climate change displaces more people, the international community may be forced to either redefine “refugees” to include climate migrants or create a new legal category and accompanying institutional framework to protect climate migrants. However, opening that debate in the current political context would be fraught with difficulty. Currently, the nationalist, anti-immigrant, and xenophobic atmosphere in Europe and the U.S. would most likely lead to limiting refugee protections rather than expanding them.

The SDGs can help, but not without an update to the US response

While there are no legally binding international regimes that protect climate migrants, there are voluntary compacts that could be used to support them. Most notably, 193 countries adopted the 2030 Sustainable Development Goals (SDGs), which address both migration and climate change.

Several of the 169 targets established by the SDGs lay out general goals that could be used to protect climate migrants. SDG 13 on climate action outlines several targets that address the climate crisis:

13.1: Strengthen resilience and adaptive capacity to climate-related hazards and natural disasters in all countries
13.2: Integrate climate change measures into national policies, strategies, and planning
13.3: Improve education, awareness-raising and human and institutional capacity on climate change mitigation, adaptation, impact reduction, and early warning.

To meet these goals, extensive bilateral and multilateral development assistance will be needed. The U.S. must create a strategic approach to focus development assistance and multilateral organizations on those targets—particularly to create resilient societies that can keep people in their communities.

Although the SDGs do not explicitly link climate change and migration, SDG target 10.7 calls for signatories to “facilitate orderly, safe, and responsible migration of people, including through implementation of planned and well-managed policies.” Again, the United States should channel multilateral development assistance to support the implementation of this target.

The scale and scope of climate change demand dynamic and comprehensive solutions. The U.S. must address climate stress on vulnerable populations specifically, rather than funneling more money into existing programs that operate on the periphery of the growing crisis.

U.S. development agencies and international development financial institutions need to redirect their development assistance to incorporate today’s unfolding climate crisis. Significantly more resources will need to be channeled to the new U.S. International Development Finance Corporation (USDFC), USAID, the Green Climate Fund, UNHCR, as well as to other critical international bodies, in particular those that make up the International Red Cross and Red Crescent organizations.

The Obama administration undertook myriad efforts to update the institutions that can address climate. Several of President Obama’s executive orders, particularly Executive Order 13677, which required incorporating climate resilience into decisionmaking on development assistance, took on the climate crisis. For the first time in the Department of Defense’s history, the 2010 Quadrennial Defense Review (QDR) recognized climate change as a “threat multiplier,” with the potential to exacerbate current challenges. 25

While the current administration has deemphasized or opposed climate-friendly approaches, the current security implications of the migration crisis might prompt a re-examination of those policies. There should be bipartisan support, particularly in the security community, for reducing the conditions that accelerate international migration.

The case for scaling up US action to confront the climate crisis

A variety of medium-term investments (five to 10 years) could create more resilience to the effects of climate change. For example, the climate change factors that push migration in Northwest Africa could—at least in part—be addressed by supporting irrigation infrastructure, providing food supplies, fostering regional water cooperation, and supporting livelihood security. 26

Dedicating greater resources to mitigate climate migration is also part of an effective solution. Research is needed to determine the best way to improve the migratory process itself—be it increasing migration monitors, providing safer modes of transport, and consolidating and expanding destination country integration resources.

This discussion is not new: In 2010, Center for American Progress staff were part of a task force that suggested a “Unified Security Budget” for the United States, to address complex crisis scenarios that transcend the traditional division of labor among defense, diplomacy, and development. 27 The need for longer-term, more calculated assessment strategies and investments has only increased over the past decade. The Pentagon already supports a variety of operational missions that respond to sudden onset climate disasters. The Navy, in particular, serves at the emergency hotline for international extreme weather events and mobilized to support the Haitian people after the 2010 earthquake, the Filipino people after the 2013 typhoon, and the Nepalis after the 2015 earthquake.

Alternatively, creating a single dedicated fund (by drawing funds from Operations and Maintenance, Research and Development, and the Refugee Assistance Fund) would allow the United States to streamline and refine its support strategies, address the effects of climate change directly, and rebuild its reputation abroad. Such a dedicated fund should try to emulate and partner with the United Kingdom’s Department for International Development (DFID), Germany’s Society for International Cooperation (GIZ), and Japan’s International Cooperation Agency (JICA). American seed funding in this area could lead to major investments of allies and partners—and in cooperation with the development agencies of these countries can mobilize massive resources at the scale required to confront the global climate crisis.

The strategies to address climate migrants presented here are far reaching, but this crisis will only intensify, and our response to it will define international relations in the 21st century.

Environmental migration and displacement: a new theoretical framework for the study of migration aspirations in response to environmental changes

L. Van Praag , C. Timmerman
Published in Environmental Sociology 6 May 2019
Environmental Science, Sociology

27 Citations

Applying insights of theories of migration to the study of environmental migration aspirations.

Highly Influenced

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How environmental change relates to the development of adaptation strategies and migration aspirations, appraising the role of the environment as a shaping element of migrants’ fragmented journeys, natural resources, human mobility and sustainability: a review and research gap analysis, a qualitative study of the migration-adaptation nexus to deal with environmental change in tinghir and tangier (morocco), gender, environmental change, and migration aspirations and abilities in tangier and tinghir, morocco, a qualitative study on how perceptions of environmental changes are linked to migration in morocco, senegal, and dr congo.

10 Excerpts

Adaptive Governance to Manage Human Mobility and Natural Resource Stress

Post-disaster (im)mobility aspiration and capability formation: case study of southern california wildfire, 69 references, environmental migration and social inequality, placing the environment in migration: environment, economy, and power in ghana's central region, the role of human agency in environmental change and mobility: a case study of environmental migration in southeast philippines, migration transitions: a theoretical and empirical inquiry into the developmental drivers of international migration, migration aspirations and migration cultures: a case study of ukrainian migration towards the european union, migration theory: quo vadis, the relevance of a “culture of migration” in understanding migration aspirations in contemporary turkey, how can migration support adaptation different options to test the migration – adaptation nexus, the internal dynamics of migration processes: a theoretical inquiry, stranded migrants and the fragmented journey.

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Published: 26 November 2019

From migration to mobility

Nature Climate Change volume 9 , page 895 ( 2019 ) Cite this article

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By many accounts, climate change is already driving human migration, but fresh thinking about the consequences of increasingly stringent borders, the intervening effects of global and local policy and how best to characterize human adaptive responses is needed to properly understand whether a crisis is on the horizon.

There is no question that climate change will impact human migration. The potential triggers are many: sea-level change leading to coastal flooding, drought destroying agricultural livelihoods, extreme heat threatening human health. By 2050, estimates for the expected number of environmental migrants are between 25 million and 1 billion. These numbers are, of course, uncertain and debated. But the idea of masses teeming from storm-ravaged and drought-stricken land is probably wrong, or at most only one small aspect of what is likely to unfold. When, where and how people will be forced to move as a consequence of climate change remains elusive, as are definitions about what it means to be a climate migrant and how best to govern the problem. In this issue and an accompanying online collection ( www.nature.com/collections/climate-migration ), we explore many of these questions and what needs to be done to improve our understanding of the complex, multi-faceted interaction between climate change and human migration.

Everything from livelihoods to identity is affected by the environments in which we live, so it makes sense that environmental change would influence decisions to stay or go. Although not always explicit, classic migration theory is generally compatible with the idea that environmental factors matter, and there is a rapidly growing literature contributing to migration–environment theory. There are a few things we know at this point: (1) migration is a fundamental strategy for addressing household risk arising from the environment; (2) environmental factors interact with broader sociopolitical histories; and (3) the migration–environment association is shaped by social networks (L. M. Hunter et al., Annu. Rev. Sociol . 41 , 377–397; 2015).

Notably, what we know about environmental migration is that a lot of non-environmental factors matter. An improved understanding of the physical processes alone is important, but as Wrathall et al. explain in this issue , exposure to sea-level change is driven concurrently by global policy decisions determining future greenhouse gas emissions and local policies at the migrants’ point of origin. To get a better handle on the space of potential outcomes, they advocate for improved modelling that prioritizes scenarios consistent with global objectives (the Paris Agreement goals), allows for consideration of local and national policies, and focuses first on predicting migration through 2050.

Migration decisions are further impacted by policies at potential destinations. Although exposure to climate risks is sure to be broad, whether climate change leads to a larger number of migrants is at least in part conditional on whether those at risk have somewhere to go. In a Perspective in this issue, Robert McLeman discusses how restrictive policies, criminalization of asylum seekers and securitization of immigration is increasingly closing the door to international migration. With nowhere to go, the vulnerable may be forced to stay put and forgo using migration as an adaptation strategy.

For example, in a News & Views article in this issue, Cristina Cattaneo explores a recent study looking at the role of migrant networks in shaping disaster-induced migration to the United States. This new research shows that prior migrants amplify international migration flows in the aftermath of hurricanes. Although the results are consistent with migration being used as an adaptive strategy, they also suggest that migration may not be a pathway available to those who need it the most. For reasons such as this, McLeman advocates for more explicit application of the United Nations Global Compact for Safe, Orderly and Regular Migration ( A/RES/73/195, 2018 ) to facilitate international migration in response to climate hazards.

Perhaps our inability to wrap our heads around the problem at the policy level arises because we have completely mischaracterized the problem that needs to be solved. In a Comment in this issue, Ingrid Boas and colleagues argue that framing climate migration as an impending security risk for the developed world hinders efforts to advance knowledge and policy that properly account for the complex nature of the problem. They argue for a reorientation of research and funding to focus on the full range of mobilities likely to result from climate change.

Environmental migration occurs both between and within countries; it may be temporary or permanent; it may follow existing routes or forge new ones. The ultimate challenge is to find solutions to reduce the climate risks that lie ahead. The need to rethink migration in terms of mobilities is pressing, especially in light of the difficulties in establishing a super-framework for climate migration. For many, the question is not whether or when they will be impacted, but how they should retreat now, and what are the costs of doing so. A News Feature in this issue highlights these very challenges for Newtok, Alaska and Isle de Jean Charles, Louisiana in the United States, both of which are in search of ways to relocate their threatened coastline communities away from the sea. Retreat may be inevitable. And, although this is unlikely to include refugees on foot crossing international borders, these residents are very much climate migrants. It is for this reason that new models, new conceptions or new policies are needed to understand the full space of human responses to climate change.

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How does climate change affect migration?

April 2021 saw a 20-year high in the number of people stopped at the U.S./Mexico border, and President Joe Biden recently raised the cap on annual refugee admissions. Stanford researchers discuss how climate change’s effect on migration will change, how we can prepare for the impacts and what kind of policies could help alleviate the issue.

In the face of a mounting humanitarian crisis at the U.S./Mexico border, the Biden administration has acknowledged climate change among the powerful forces pushing migrants from Central America. A $4 billion federal commitment to address the root causes of irregular migration acknowledges the need for adaptation efforts to help alleviate the situation.

Homes in Nicaragua flooded by Hurricane Eta

The challenge is not limited to the border. Last year, weather-related disasters around the world uprooted 30 million people – more than the population of the 14 largest U.S. cities combined – and wildfires displaced more than a million Americans, according to the Internal Displacement Monitoring Centre.

Below, Stanford climate and behavior experts discuss how climate change’s effect on migration will change, how we can prepare for the impacts and what kind of policies could help alleviate the issue. The researchers include Chris Field , a climate scientist who has led UN Intergovernmental Panel on Climate Change efforts to analyze climate-related risks, impacts and adaptation opportunities; Gabrielle Wong-Parodi , a behavioral scientist who studies how people react to challenges associated with global environmental change; Erica Bower , a PhD student who studies human mobility in the context of climate change impacts and served as a climate change and disaster displacement specialist at the UN Office of the High Commissioner for Refugees; Nina Berlin Rubin , a PhD student in Earth system science whose research focuses on decision-making in the face of climate extremes.

What is a common story of climate migration in the U.S./Mexico?

Bower : Climate change is a threat multiplier – it can exacerbate economic insecurity or political instability, which in turn may lead to migration. In the “dry corridor” of Central America, for example, climate change extremes such as droughts may hinder crop production. Without a consistent source of food or income, a farmer may seek other livelihood opportunities in a nearby city or further north. When combined with poverty or violence, a drought may make the perilous journey north seem to be a more promising adaptation or survival strategy.

How has climate change’s effect on the tide of refugees in the U.S./Mexico border changed in recent years?

Bower : In recent years, climate change has made extreme weather events stronger and more frequent, which may contribute to migration decisions. However, given the multiple reasons why people move, we do not have the evidence required to say with certainty precisely how climate change has affected net migration flows to the U.S./Mexico border.

What does the future hold for climate-related migration at the border? What should we expect, and how should we prepare for it?

Field : In the long run, stopping climate change is a key element of getting the situation under control. In the short run, there are lots of effective ways to decrease vulnerability. These range from improving agricultural practices to strengthening social safety nets. Across the full suite of possible vulnerability reduction measures, it is critical that the solutions are implemented in partnership with local communities and not imposed on them. In regions with high levels of corruption or political or criminal violence, it is much more challenging to make progress on vulnerability reduction.

Bower : We may need to change our approach to welcoming people across our southern border. The definition of refugee in international law is very narrow, and most people fleeing in climate change contexts – including from Central America to the U.S./Mexico border – are generally not recognized as refugees under international or domestic law. Newly proposed legislation in Congress would protect the human rights of people fleeing to the U.S. in the context of climate change.

Leaving is only half the story. Tracking these migration pathways from origin to destination can speak to whether people are moving to safer areas or to areas that introduce new or heightened risks. ” Nina Berlin Rubin PhD student, Department of Earth System Science

How extensive is climate change’s effect on migration within the U.S.?

Wong-Parodi : We are seeing some evidence that people who feel more impacted by wildfires and secondary impacts like smoke are more likely to intend to move to a new state within the U.S. or even out of the country. The question that remains is whether the destination they are planning on moving to is more or less at risk for wildfires or other climate hazards.

Berlin Rubin : Exactly. One might decide to uproot their family and leave behind friends and neighbors in search of respite from wildfires and smoke, only to find themselves living somewhere with just as much wildfire risk – or exposure to other risks like flooding – as where they were before. And the reality is, as these fires become more frequent and destructive, people will have fewer options and less confidence that their destination is actually going to be free from wildfires.

Bower : We are also seeing that many communities are seeking government support to relocate away from sea level rise or flooding. A recent mapping exercise identified 36 cases of community-wide relocation in the U.S. alone since 1970.

How might federal and state policy lessen climate change’s impact role as a driver of migration at the border and within the U.S.?

Field : The U.S. Federal government can play a large role in addressing the core drivers of displacement, through three main pathways. It can decrease its contribution to warming through decreasing its greenhouse gas emissions. It can help other countries decrease their emissions through financial and technical assistance. It can also help poor countries adapt so that their people feel less pressure to migrate. This last pathway has the potential to be especially cost-effective in the near term, even though it cannot address all of the drivers of migration.

Is there any promising research/data gathering that could dramatically change how we understand and react to this challenge?

Field : It is likely that progress in decreasing pressure to migrate will require patience. One area where data can make a big difference is in cataloging investments in adaptation and following their consequences. At this point, we are not systematically cataloging and tracking adaptation efforts. A robust database can be the foundation for a new generation of evidence-based adaptation.

Berlin Rubin : Research at the individual level will help us better understand and characterize the psychosocial and experiential factors that motivate climate-related migration decisions. But leaving is only half the story. Tracking these migration pathways from origin to destination can speak to whether people are moving to safer areas or to areas that introduce new or heightened risks. We need to understand the local context in which people are making their decisions in order to get ahead of these challenges.

Field is the Perry L. McCarty Director of the Stanford Woods Institute for the Environment , the Melvin and Joan Lane Professor for Interdisciplinary Environmental Studies, a professor of Earth system science and biology and a senior fellow at the Precourt Institute for Energy . Wong-Parodi is an assistant professor of Earth system science in the School of Earth, Energy & Environmental Sciences ; and a center fellow at the Stanford Woods Institute for the Environment . Bower is a PhD student in the Emmett Interdisciplinary Program in Environment and Resources at Stanford’s School of Earth, Energy & Environmental Sciences.

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How does climate change affect disease.

As the globe warms, mosquitoes will roam beyond their current habitats, shifting the burden of diseases like malaria, dengue fever, chikungunya and West Nile virus. Researchers forecast different scenarios depending on the extent of climate change.

The effects of climate change on water shortages

In Jordan, one of the most water-poor nations, predictions of future droughts depend on the scale of climate change. Without reducing greenhouse gases the future looks dry, but researchers offer some hope.

Media Contacts

Chris Field Stanford Woods Institute for the Environment (650) 823-5326; [email protected]

Gabrielle Wong-Parodi School of Earth, Energy & Environmental Sciences (650) 725-6457; [email protected]

Erica Bower School of Earth, Energy & Environmental Sciences (203) 666-9892; [email protected]

Nina Berlin Rubin School of Earth, Energy & Environmental Sciences (307) 690-4234; [email protected]

Rob Jordan Stanford Woods Institute for the Environment (650) 721-1881; [email protected]

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6 6 Environmental Migration∗

Published: January 2011
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Environmental migration is not a new phenomenon. Natural and human-induced environmental disasters have displaced people in the past and continue to do so. Nevertheless, the environmental events and processes accompanying global climate change threaten to dramatically increase human movement both within and across State borders. Estimates suggest that between 200 and 250 million people will be displaced by environmental causes before 2050. The environmental impacts of climate change have been signalled as the key driver of this anticipated surge in migration.Evidently, migration on this unprecedented scale demands a multilateral institutional response. Yet, environmental migration governance represents a significant challenge, not least because the content and parameters of the concept continue to be debated. There is at present no internationally agreed definition of what it means to be an environmental ‘migrant’, ‘refugee’, or ‘displaced person’, and, consequently, no agreed label for those affected. Questions of definition have clear governance implications, informing the appropriate location of environmental migration both procedurally—as an international, regional, or local, developed and/or developing country concern/responsibility—and thematically—for example, within the existing refugee protection framework or under the UN Framework Convention on Climate Change. The viability and value of institutionalizing international cooperation and collaboration on international migration matters generally, and environmental migration particularly, depends upon how that phenomenon can and should be formulated as a discrete concept in law and policy. Taking a legal perspective, this chapter grounds its normative analysis in a thorough examination and assessment of the existing institutions and political processes that impact upon environmental migration and States' responses to them.

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A systematic review of climate migration research: gaps in existing literature

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Published: 16 April 2022
Volume 2 , article number 47 , ( 2022 )

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Rajan Chandra Ghosh ORCID: orcid.org/0000-0001-9027-6649 1 , 2 &
Caroline Orchiston ORCID: orcid.org/0000-0002-3171-2006 1

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Climatic disasters are displacing millions of people every year across the world. Growing academic attention in recent decades has addressed different dimensions of the nexus between climatic events and human migration. Based on a systematic review approach, this study investigates how climate-induced migration studies are framed in the published literature and identifies key gaps in existing studies. 161 journal articles were systematically selected and reviewed (published between 1990 and 2019). Result shows diverse academic discourses on policies, climate vulnerabilities, adaptation, resilience, conflict, security, and environmental issues across a range of disciplines. It identifies Asia as the most studied area followed by Oceania, illustrating that the greatest focus of research to date has been tropical and subtropical climatic regions. Moreover, this study identifies the impact of climate-induced migration on livelihoods, socio-economic conditions, culture, security, and health of climate-induced migrants. Specifically, this review demonstrates that very little is known about the livelihood outcomes of climate migrants in their international destination and their impacts on host communities. The study offers a research agenda to guide academic endeavors toward addressing current gaps in knowledge, including a pressing need for global and national policies to address climate migration as a significant global challenge.

Climate-Conflict-Migration Nexus: An Assessment of Research Trends Based on a Bibliometric Analysis

Scales and sensitivities in climate vulnerability, displacement, and health

Climate change-induced migration: a bibliometric review

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Introduction

Population displacement can be driven by climatic hazards such as floods, droughts (hydrologic), and storms (atmospheric), and geophysical hazards such as earthquakes, volcanic eruptions, and tsunami (Smith and Smith 2013 ). The interactions between natural hazard events, and social, political, and human factors, frequently act to intensify the negative effects of climatic and geophysical hazards, leading to political and social unrest, increased social vulnerability, and human suffering. As a consequence of these adverse effects, people migrate from their native land, causing stress, uncertainty, and loss of lives and properties. However, such migration can also have positive impacts on migrants’ lives. For example, migrants may be able to diversify their livelihood and have greater access to education or healthcare.

In 2020, 30.7 million people from 149 countries and territories were displaced due to different natural disasters. Among them, climatic disasters were solely responsible for displacing 30 million people within their own country, with the highest recorded displacement occurring in 2010 when 38.3 million people were displaced (IDMC 2021a ; IOM 2021 ). It is difficult to estimate the actual number of people that moved due to the impacts of climate change (Mcleman 2019 ), because peoples’ migration decisions are triggered by a range of contextual factors (de Haas 2021 ). Nevertheless, the Internal Displacement Monitoring Centre (IDMC) states that approximately 283.4 million people were displaced internally between the years 2008 and 2020 because of climatic disasters across the globe (Table 1 ). This number represents almost 89% of the total disaster-induced displacement that occurred during this timeframe (IDMC 2021a ).

People who move from their homes due to climate-driven hazards are described in a range of ways, including climate migrants, environmental migrants, climate refugees, environmental refugees, and so on (Perkiss and Moerman 2018 ). The process of migration related to climate-driven hazards is variously described as environmental migration, environmental displacement, climate-induced migration or climigration (Bronen 2008 ).

In this research, we focus on climate-induced migration more specifically induced by slow-onset climatic disasters (sea-level rise, drought, salinity etc.), rapid onset extreme climatic events (storms, floods etc.), or both (precipitation, erosion etc.). This study investigates how climate change-induced migration studies are framed in the existing literature and identifies key gaps in the published literature.

There is a significant ongoing debate about the links between climate change and human migration in the academic literature. Some researchers strongly believe that climate change directly causes people to move, whereas the others argue that climate change is just one of the contextual factors in peoples’ migration decisions (Laczko and Aghazarm 2009 ). Although there are scholarly opinions that call into question climate change as a primary cause of migration (Black 2001 ; Black et al. 2011 ; McLeman 2014 ), there is also evidence that climate change causes severe environmental effects and exacerbates the vulnerabilities of people that force them to leave their place of living (Bronen and Chapin 2013 ; Laczko and Aghazarm 2009 ; McLeman 2014 ).

Moreover, the relationship between the adverse effects of climate change and different types of human mobility (migration, displacement, or planned relocation) has become increasingly recognized in recent years (Kälin and Cantor 2017 ). It is assumed in general that the number of climate displaced people is likely to increase in future (Mcleman 2019 ; Wilkinson et al. 2016 ), and climate change could permanently displace an estimated 150 million to nearly 1 billion people as a critical driver by 2050 (Held 2016 ; Perkiss and Moerman 2018 ). As the number of climate migrants increases rapidly in some areas of the world (IDMC 2017 ), it is now confirmed as a significant global challenge (Apap 2019 ) and recognized as a considerable threat to human populations (Ionesco et al. 2017 ).

Climate migration has multifaceted impacts on peoples’ livelihoods. Being displaced from their home, people migrate within their own country, described as internal migration, or across borders to other countries known as international migration. Internal movements of climate migrants occur mostly to nearby major cities or large urban centers (Poncelet et al. 2010 ). Climate migrants who try to move internationally are significantly challenged by two different security problems. Firstly, they cannot live in their own homeland because of worsening climatic impacts and are forced to leave their ancestral land. Secondly, they cannot move to other countries quickly to find a safer place because, according to international law, climate migrants are not refugees and they are not supported by the UN Refugee Convention or any international formal protection policies (Apap 2019 ; Mcleman 2019 ). In this situation, they live with significant livelihood uncertainty. The United Nation’s Sustainable Development Goals (SDGs) and the Sendai Framework for Disaster Risk Reduction (SFDRR) recognize them as a key group that is highly exposed and vulnerable because of their circumstances (Ionesco et al. 2017 ). Hence, policy development to address complex climate migration issues has become an emerging priority around the globe (Apap 2019 ).

In order to address this global challenge, there has been growing academic and policy attention focused on regional (Kampala Convention-2009 by African Union), national (Nansen Initiative—2012 by Norway and Switzerland), and international (Global Compact for Safe, Orderly and Regular Migration- 2018 by United Nations) levels of climate-induced migration in recent years. Myers’s ( 2002 ) seminal article signposted environmentally driven migration as one of the most significant challenges of the twenty-first century, and later, similar assumptions were made by Christian Aid (Baird et al. 2007 ), IOM (Brown 2008 ), and Care International (Warner et al. 2009 ). Such predictions led to a proliferation of the academic discourse on migration, focused on national and international security, policy frameworks, and human rights (Boncour and Burson 2009 ). Other studies have focused on vulnerability assessment, risk reduction, adaptation, resettlement, relocation, sustainability, and resilience, considering pre-, during and post-disaster circumstances of climate migration (Bronen 2011 ; Bronen and Chapin 2013 ; IDMC 2019 ; IOM 2021 ; King et al. 2014 ).

This research contributes to the discourse by identifying the gaps in the published literature regarding climate migration. A systematic literature review was undertaken to shed light on the current extent of academic literature, including gaps in knowledge to develop a climate migration research agenda. Two notable review papers provided a solid foundation for this endeavor. First, Piguet et al. ( 2018 ) developed a comprehensive review of publications on environment-induced migration from a global perspective based on a bibliographic database—CliMig. Their detailed mapping of environmentally induced migration research focused on five categories of climatic hazards (droughts, floods, hurricanes, sea-level rise, and rainfall); however, it did not include salinity and erosion which are also climate-driven and has direct effects on internal and international migration (Chen and Mueller 2018 ; Mallick and Sultana 2017 ; Rahman and Gain 2020 ).

The second key review paper was by Obokata et al. ( 2014 ), which provided an evidence-based explanation of the environmental factors leading to migration, and the non-environmental factors that influence the migration behaviors of people. Their scope of analysis was limited to international migration and excluded other types of migration, such as internal climate-induced migration.

Although migration, or more specifically environmental migration, was occurring over many decades of the twentieth century, the IPCC First Assessment report was released in 1990, which presented the first indications of the risks of climate change-induced human movement (IPCC 1990 ). This milestone report then stimulated the academic discourse, and consequently, a rapid increase in climate migration publication resulted. For this reason, the current study undertook a systematic review of literature across three decades beginning in 1990 and ending in 2019. This study aims to understand how the published literature has framed the climate-induced migration discourse. This paper identifies the key gaps in existing scholarship in this field and proposes a research agenda for future consideration on current and emerging climate migration issues.

In the following section, we outline the systematic review method and identify how journal articles were searched, selected, reviewed, and analyzed. In the next section, we present the results of this study. Results are organized into four subsections that illustrate the reviewed literature in the following ways—spatial and temporal trends, disciplinary foci, triggering forces of migration, and other key issues. Finally, we conclude by identifying research gaps, addressing the limitations of this study, and presenting a research agenda.

Methodology

We have adopted a systematic review methodology for this study because it provides an …overall picture of the evidence in a topic area which is needed to direct future research efforts (Petticrew and Robert 2006 ). Systematic reviews reduce the bias of a traditional narrative review, although it is challenging to eliminate researcher bias while interpreting and synthesizing results (Doyle et al. 2019 ). It also limits systematic bias by identifying, evaluating, and synthesizing all relevant studies to answer specific questions or sets of questions, and produces a scientific summary of the evidence in any research area (Petticrew and Robert 2006 ). Moreover, systematic reviews effectively address the research question and identify knowledge gaps and future research priorities (Mallett et al. 2012 ). We have adopted this approach following the methodology developed by Berrang-Ford et al. ( 2011 ) which was tested in the field of environmental and climate change studies, with measurable outcomes. We have conducted the review following these four steps—article search, selection, review, and analysis (Fig. 1 ).

Systematic review flowchart

Article search

We conducted a comprehensive literature search to identify the published academic literature on climate-induced migration to develop a clear understanding of this field of study. We identified sixteen commonly used keywords to search for articles that are predominantly used in the literature. ProQuest central database was selected and used in consultation with a skilled subject librarian to search for the relevant articles for this study. We conducted this literature search in July 2019 using the key thesaurus terms, presented in Table 2 . All keywords were then searched individually in the publication’s title and abstract. We only considered English language peer-reviewed articles for this study, published between the years 1990 and 2019 (up to June).

Article selection

The main purpose of this process was to ensure the selection of appropriate literatures for further analysis. We approached the Preferred Reporting Items for Systematic Reviews and Meta Analyses (PRISMA), a systematic evaluation tool, which was also used by Huq et al. ( 2021 ). In stage one of the selection process, 277 articles were counted based on our search criteria. In stage two, we excluded 25 duplicates, and 252 articles remained for further assessment. In the third and final stage of the detailed assessment of each paper, we identified a further 91 publications that were not relevant to our study but appeared in our searched list because search terms were briefly mentioned in their title and/or abstract without being described in further detail. As these articles did not fit with the aim and content of this research, we excluded those 91 and selected a final 161 articles for this study.

Article review

All the selected articles were then considered for detailed review in order to achieve the purpose of the study. A questionnaire (Online Attachment—A) was developed partially following Berrang-Ford et al. ( 2011 ); Obokata et al. ( 2014 ) and Piguet et al. ( 2018 ) to investigate how climate migration studies are framed in the published literature. Then each article was reviewed in detail in response to the individual parameters of the questionnaire such as general information ( article title, authors name, publication year, journal, discipline, content ), methodological approach ( qualitative, quantitative, mixed ), focused study areas ( country, climatic zones ), source of migrants ( rural, urban ), migration types ( internal, international ), impacts of climate migration ( social, economic, political, health, cultural, environmental, security ), causes of migration ( climatic: flood, sea-level rise, drought etc ., other: socio-economic, political, cultural ), target communities ( displaced community, receiving community ), and livelihoods ( housing, income, employment, etc . ) of climate migrants described in the publications.

Article analysis

All the data were recorded in Microsoft Office Excel spreadsheets. Relevant data for each parameter were filtered, analyzed, and summarized using the necessary Excel tools. Referencing was compiled through Mendeley Desktop.

Spatial and temporal trend

General information.

In this section, the publication date of the reviewed articles was used in order to identify the development of the academic discourse in climate migration studies over the last three decades (1990–2019). Results show the increasing focus of academic attention on this area of research over that timeframe. The study found only four publications between the years 1990 and 1999. During 2000–2009, an additional 16 articles were published, which was followed by an almost 90 percent (141 publications) increase in reviewed articles over the period of 2010–2019 (Table 3 ).

Reviewed study areas

In 84 reviewed articles, the study reported research focused on a particular location, and in some cases, they considered two or more areas for their research. Therefore, multiple counting for each study has been considered, which represents all the continents except Antarctica. The analysis shows that Asia (38%) is the continent with the greatest number of climate migration studies, followed by Oceania (20%), North America (17%), and Africa (14%). In contrast, Europe and South America have received less attention, with 7% and 5%, respectively. Table 4 presents the distribution of study areas by continent focused on the reviewed papers.

Climatic zones of the reviewed studies

This study identified the climatic zones of the study areas in order to find out which zones are most commonly studied among the reviewed studies. We adopted the climatic zones of the world from Peel et al. ( 2007 ), which is the updated version of Koppen’s climate classification, and categorizes the world climate into five major zones, i.e., (i) tropical, (ii) arid, (iii) temperate, (iv) cold, and (v) polar. This review shows that 86 publications mentioned their study areas, equating to 54% of the total reviewed papers. Among them, 81% referred to a specific region as their study area. The study areas were then classified into the above-mentioned climatic zones with one reference offered randomly for each country as an example of the range of research that has been conducted.

This study reveals that 49% of this group (among 81%) focused on tropical climatic areas such as Bangladesh (Islam et al. 2014 ), Cambodia (Jacobson et al. 2019 ), Kiribati (Bedford et al. 2016 ), Papua New Guinea (Connell and Lutkehaus 2017 ), Philippines (Tanyag 2018 ), Tuvalu (Locke 2009 ), and Vanuatu (Perumal 2018 ) among others, and 16% focused on arid climatic zones such as African Sahel (McLeman and Hunter 2010 ), Israel (Weinthal et al. 2015 ), Peru (Scheffran 2008 ), and Senegal (Nawrotzki et al. 2016a , b ). In addition to these, 13% of authors focused on temperate regions, i.e., Mexico (Nawrotzki et al. 2016a , b ), Nepal (Chapagain and Gentle 2015 ), Taiwan (Kang 2013 ), UK (Abel et al. 2013 ), and the USA (Rice et al. 2015 ) for their study and 3% focused on cold climatic areas, i.e., Alaska: USA (Marino and Lazrus 2015 ), Canada (Omeziri and Gore 2014 ), and northern parts of China (Ye et al. 2012 ). No studies were found based on polar regions (Fig. 2 ). Some studies did not specify a region or country of study but instead focused on broader regions such as Africa (White 2012 ), Asia–Pacific (Mayer 2013 ), Europe (Werz and Hoffman 2016 ), Latin America (Wiegel 2017 ), and Pacific (Hingley 2017 ).

Climatic zones of the reviewed study areas-adopted from Peel (2007)

Migration types and sources of climate migrants

Migration types here refer to whether migration was internal (within a country or region) or international (across borders), and sources of climate migrants refer to people from rural or urban source regions. Most authors (73%) mentioned nothing regarding migration types, but a quarter (27%) explicitly discussed internal or international migration. Among them, 11% described climate migration within countries and 10% investigated cross-border migration. Some authors (6%) were concerned with both internal and international climate migration. Source regions for climate migrants were not often considered, with only 19 publications mentioning the origin of migrants. Among these, 11 articles stated that migration occurred from rural areas, and two publications discussed migration from urban areas. Also, six articles described climate migration from both rural and urban areas.

Disciplinary foci

Research discipline.

This study reveals that climate migration studies are becoming more focal issues in different research disciplines that include more than 40 subject areas. Hence, we developed a typology for the reviewed articles based on the relevant research themes. The typology consists of six research disciplines, each of which includes different subjects, as follows.

Social sciences: Social sciences, Sociology, Political Science, International Relations, Comprehensive Works, Population Studies, Anthropology, Social Services and Welfare, History, Philosophy, Ethnic Interests, Civil Rights, Women's Studies

Geography and environment: Meteorology, Environmental Studies, Energy, Conservation, Earth Sciences, Geography, Agriculture, Geology, Biology, Archaeology, Pollution

Business studies and development: Management, Business and Economics, International Commerce, International Development and Assistance, Economics, Insurance, Investments, Accounting

Law, policy, and planning: Law, Military, Civil Defense, Criminology and Security, Environmental policy

Health and medical science: Public Health, Psychology, Medical Sciences, Physical Fitness, and Hygiene

Other: Literature, Library and Information Sciences, Physics, Technology

Among the reviewed publications, some articles were discussed from the perspective of one particular discipline, while others came from two or more disciplines. Therefore, multiple counting for each discipline was considered during the analysis. The study reveals that Social Science covers the highest percentage of publications (41%), followed by Geography and Environment (30%), Business Studies and development (10%), Law, policy and planning (9%), and Health and medical science (7%). Only 2% of publications are not covered by any of these disciplines.

Primary research themes

The authors discussed a diverse range of themes in the reviewed articles. Key themes have been classified into eight categories based on their topics and focusing subjects. Some of the publications focused on multiple themes, which were counted separately under each theme. Most of the authors (27%) focused on Politics and policy issues, and almost a fifth (18%) of total articles focused on the themes of population, health, and development issues. Human rights, conflicts, and security issues were discussed in 16% of papers, and climate, vulnerability, adaptation, and resilience topics were the focus of 12% of publications. In 11% of publications, the authors focused on identity and cultural issues, and socio-economic topics comprised a further 9% of the total. Environmental issues were discussed by 4% of reviewed articles and 3% of publications did not fit into any of the above categories and are described as Other.

Methodological approaches

This review identified that researchers applied both qualitative and quantitative methods in climate migration research. A total of 82% of the reviewed articles used qualitative methodologies, and 9% quantitative. In addition to these, 9% of articles used mixed methods in climate migration research. Of those who used qualitative studies, most were review-based (86%), comprising systematic review, empirical evidence-based review, critical synthesis review, critical discourse review, and policy review. Only 14% of qualitative studies used interview methods (7%), case studies (6%), and focus group discussion (1%). Data sources reported in the reviewed literature for the quantitative research included secondary data (73%), historical data (13%), remote sensing data (7%), and survey data (7%).

Triggering forces of migration

Climatic causes of migration.

The reviewed publications outlined a range of different causes of climate migration. This study reveals nineteen climate-related causes of migration. We merged these causes into eight categories, defined as (i) climate change (climate change, global warming, temperature, environmental change, climate-induced natural disaster, meteorological events, extreme weather, heatwave), (ii) flood, (iii) sea-level rise (sea-level rise, melting glacier), (iv) drought (drought, desertification), (v) storm (storm, cyclone, hurricane, typhoon), (vi) salinity (salinity, tidal surge), (vii) precipitation-induced landslide, and (viii) erosion (coastal erosion, river erosion). “Climate change” is defined as a separate category because some publications named climate change as an overarching driver of migration, rather than specifying any particular hazard. In 70 publications, authors mentioned particular climatic events that were solely responsible for human migration, and 53 of these articles predominantly identified climate change as the main driver of migration, followed by sea-level rise (6), drought (4), flood (3), storm (2), and precipitation-induced landslide (2). In the remaining articles, scholars identified two or more climatic events that were collectively responsible for human displacement. Based on these articles, multiple counting for each climatic event was considered and the results show that climate change was the most commonly cited cause in 126 articles, along with other climatic causes. The authors also identified sea-level rise, drought, flood, and storms as the significant drivers of peoples’ migration along with other climatic drivers, which were mentioned in 51, 46, 44, and 43 articles, respectively. Precipitation-induced landslide and erosion were recognized in 17 and 12 articles, respectively, as the causes of human displacement, whereas eight articles identified salinity as the main reason.

Influencing causes of migration

Although this review was focused on identifying the climatic causes of human displacement, some other causes emerged during the analysis that also influence migration. In 68 publications, economic, social, environmental, political, cultural, and psychological causes were stated as drivers of migration, in addition to the climatic causes. Among these, economic causes (32%) have been identified as the most common driver, followed by social (25%) and environmental (22%) causes. Some articles described political causes (16%), and the remainder mentioned cultural (3%) and psychological (1%) drivers of migration.

Other key issues

Impacts of climate migration

One of the key findings of this review concerns the impacts of climate migration. In 48 publications, authors described a range of different impacts caused by climate migration, such as social, economic, political, health, cultural, environmental, and security. All the impacts were identified based on the location of climate migrants which are classified into the following three categories: (i) impacts on the place of origin, (ii) impacts on the place of destination, and (iii) impacts on both origin and destination. The review demonstrates that the impacts of climate migration were more frequently identified for the place of origin rather than for the destination. In the place of origin, authors discussed the economic, social, and cultural impacts, compared to political, security, health, and environmental impacts. In contrast, in the destination, scholars were more focused on security and cultural impacts. Overall, security, cultural and economic impacts were the most frequently discussed themes by the authors of reviewed literature in comparison with other impacts (Table 5 ).

Discussed communities

More than half of the reviewed articles ( N = 81) described climate migrants and/or their receiving communities. In most of the discussions, authors talked about both displaced and host communities together (57%). In more than two-fifths of articles, they considered only displaced communities (42%). In contrast, none of the authors of the reviewed literature discussed host communities in detail in their publications, except Dorent ( 2011 ). Only a few authors briefly mentioned host communities during the discussion of climate migration impacts.

Livelihoods of climate migrants

This review demonstrates that the overall livelihood of climate migrants has not been a key focus in any of the reviewed literature. However, a few separate parameters of livelihoods, including housing, income and employment, health, access to resources, and education were mentioned in 23 articles. The analysis shows that the livelihoods of migrants in their place of origin (71%) were more likely to be considered compared to their destination (11%). In some articles (18%), authors addressed the livelihoods of climate migrants considering both their place of origin and destination. In total, all the articles which considered livelihoods had a specific focus on internal migration, and none mentioned the livelihoods of climate migrants in terms of international migration.

Discussion and research gaps

Climate change-induced migration is neither new (Nagra 2017 ), nor a future hypothetical phenomenon—it is a current reality (Coughlin 2018 ). This review provides a comprehensive analysis of how this field of study is framed in the existing literature. The academic discourse on human migration due to climate change is suggestive of a long-standing causal connection, which is hard to dissociate (Milán-García et al. 2021 ; Parrish et al. 2020 ; Piguet et al. 2011 ).

The review of spatial and temporal trends of climate-induced migration studies illustrates the growth in the field since the release of 1st IPCC report in 1990. In addition, this review has explored some basic questions that are useful to guide future research in this field of study, for instance, which study areas have received greater or lesser focus? Where are these study areas located in relation to global climatic zones? How are people migrating, i.e., internally, or internationally? What are the spatial sources of climate-induced migrants, i.e., rural, or urban environments?

This review also demonstrates that the expansion of climate migration research increased rapidly after 2000, although the studies in this field began before 2000 (Table 3 ). It denotes that the global academia and policymakers have emphasized their focus on this topic in recent decades (Milán-García et al. 2021 ; Piguet et al. 2011 ). Moreover, this review identifies the Asia–Pacific region as the global ‘hotspot’ of climate migration research (Table 4 ). This reflects the IDMC ( 2019 ) report that states more than 80% of the total displacement between 2008 and 2018 occurred within this region. Moreover, a significant proportion of global environmental displacement will continue to occur in the Asia–Pacific region (Mayer, 2013 ). Therefore, this region could be considered as a critical ‘living laboratory’ for future climate migration research.

Climate migration is mostly occurring internally (IDMC 2021a ; Laczko and Aghazarm 2009 ), and in recent years, it has been widely acknowledged in the policy areas (Fussell et al. 2014 ; The World Bank 2018 ). Nevertheless, this study reveals that only a quarter of the reviewed studies for example, Chapagain and Gentle ( 2015 ), Islam et al. ( 2014 ), and Prasain ( 2018 ) have considered the migration types (internal or international) and sources (rural or urban) of climate migrants in their research. Thus, this review identifies the gap and need for contributions to the academic discourse that investigate migration types, the origin of migrants, and their patterns of migration.

The review of the disciplinary foci of climate-induced migration literature reveals that a broader range of disciplines are now focusing on this research topic, which suggests that greater interdisciplinarity is developing in the discourse. IDMC ( 2021b ) data presented in Table 1 show that climate-induced disasters are displacing millions of people every year, but surprisingly none of the reviewed publications appeared under the subject category of disaster management in the database. This reflects the emergent nature of the academic discourse on climate migration and disaster management, which includes recent studies by Ye et al. ( 2012 ), Tanyag ( 2018 ), and Hamza et al. ( 2017 ). In addition, politics and policy issues regarding climate migration were discussed by scholars; however, no country-specific policies were found during the review that considered both the origin and host communities of climate migrants.

Campbell ( 2014 ) argues that there is insufficient empirical evidence within climate migration research. However, this review reveals that research in this area has been undertaken using a range of methodologies, from qualitative (review, case study, interview, focus group discussion etc.) to quantitative (based on survey data, secondary data, historical data, and remote sensing data), which has produced a strong foundation of work to guide future pathways for interdisciplinary climate migration research. A significant proportion of the research to date has been review-based. Also, there is a lack of empirical studies in this research field that consider the application of geographic information system and remote sensing.

It is clear from reviewing the triggering forces of climate-induced migration literature that climatic events are dominantly responsible for climate migration, which is supported by Rahman and Gain ( 2020 ), Connell and Lutkehaus ( 2017 ), Gemenne ( 2015 ), and Kniveton et al. ( 2012 ). Despite this, there are some other influencing push and/or pull factors such as socio-economic, political, cultural, etc., which are likely to compound (or be compounded by) climate impacts, to trigger the migration process (Black et al. 2011 ; de Haas 2011 , 2021 ; Fussell et al. 2014 ). While there remains ample anecdotal evidence of the relationship between climate change impacts and migration, the specific reasons for people to decide to migrate are interwoven with indirect pressures, such as livelihood disruption, poverty, war, or disaster (Werz and Hoffman 2016 ). Moreover, why people choose to stay at their places is also essential in the context of creeping environmental and climate-induced migration (Mallick and Schanze 2020 ).

One of the other key issues reviewed in this study is that the literature to date fails to build an understanding of the impacts of climate migration on both the origin (source regions) and destination of the climate migrants. There are very few studies such as Comstock and Cook ( 2018 ), Maurel and Tuccio ( 2016 ), Pryce and Chen ( 2011 ), Rahaman et al. ( 2018 ), Rice et al. ( 2015 ), and Schwan and Yu ( 2017 ) that investigate different aspects of socio-economic impacts (housing, health, social, economic, etc.) of climate migration in the destination region, and this presents a clear gap in knowledge that requires further study. Also, no current research has been identified during the review that focused on the environmental impacts of climate migration.

In addition, this review identifies that there was less attention paid to the impacts of climate migration on host communities compared to displaced populations in their new locations. Given that migration will continue to increase globally, there is likely to be a growing need to understand the range of potential impacts on host communities. Although some countries and regions are developing policies to manage internal migration, there are no formal protection policies for cross-border climate migration (Nishimura 2015 ; OHCHR 2018 ; Olsson 2015 ; Zaman 2021 ). Therefore, policy arrangements for managing the needs of climate displaced people in their new communities need to be developed to account for issues related to impacts, livelihoods, community cohesion, and cultural diversity and values. Future research should address the significant gap in understanding the livelihoods of climate migrants in their cross border or international destination. More specifically, in developed countries where the employment sector is more formalized, there is less room for informal economic practices that are common in developing contexts. More formal employment arrangements make it challenging for migrants to establish new livelihoods, alongside other challenges such as language barriers, and other financial, social, cultural and well-being issues.

Limitations and future research scope

Limitations of this study.

There are some limitations to this systematic review; firstly, this review used ProQuest as the sole database for the analysis, and future work could extend the scope to include other major databases. Secondly, this study only considered English language literature, and there are likely to be significant publications in other languages relating to climate migration that were not included in this analysis. Thirdly, looking at pre-1990 or post-2019 literature could add more exciting findings to the search list, which would provide more informative literature. Finally, the outputs of this review are limited to the nature of the search terms, and thus, if other words or texts such as climate-induced relocation or mobility were used, it might extend the range of the review.

Toward a research agenda for climate migration

This review has highlighted several exciting future research opportunities that will build on the strong foundation of work over the past decades in the field of climate migration studies. These include the following research themes; (i) a richer understanding of the full range of impacts (such as social, economic, environmental, and cultural) of climate migration on host communities; (ii) in-depth analysis of the livelihoods of climate-induced migrants in their new destination; (iii) evidence-based research on internal and international climate migration with their sources; (iv) long-term migration policy development at national, regional, or international levels considering both climate migrants and host communities; (v) scope and application of geographic information systems and remote sensing in this area of research, and (vi) developing sustainable livelihood frameworks for climate migrants. The authors believe that academic contributions to these research themes will drive climate migration challenges toward long-term solutions, particularly in those countries that are going to be hosting increasing numbers of climate migrants in future.

This study aimed to understand the past three decades of academic endeavor on climate migration and to identify the gaps in the existing literature in order to inform a research agenda for future research. Climate change, climate-induced migration, and climate migrants are now considered significant global challenges. Climate migrants are identified as a vulnerable group, and a consideration of issues for this group is essential in addressing the goals of the SDGs and SFDRRR. There is a growing body of knowledge that reflects the global relevance of climate migration as a major current and future challenge (Boncour and Burson 2009 ). Addressing the issues and challenges of this form of migration will improve the survival and certain resettlement rights of climate migrants (Miller 2017 ). Therefore, this review contributes a research agenda for future climate migration studies. This study has revealed a critical need to establish a universally agreed definition of ‘climate-induced migrants’ and ‘climate-induced migration,’ which remains unclear to date. Lack of clarity only acts to reduce the visibility of issues related to climate-induced migration. In addition, there is a crucial need to improve the evidence base for climate-induced migration by improving current global datasets, to inform local, regional, and global policy development. Policies need to be future-looking in preparation for a rapid and significant increase in climate-related migration across the globe, within and across national borders. For instance, it is important for receiving countries to anticipate an upsurge in migration by developing appropriate policies to support new migrants, particularly regarding visa and immigration arrangements. Addressing current gaps in knowledge will lead to improved pathways to manage this global migration challenge, which is now a critical need if we are to achieve a sustainable future in a climate-challenged world.

Data availability

Data are available from the corresponding author upon reasonable request.

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Acknowledgements

The authors would like to thank Dr Douglas Hill, Dr Ashraful Alam and Dr Bishawjit Mallick for their feedback on the initial draft of this article.

This research has been supported by a University of Otago Doctoral Scholarship. Open Access funding is enabled and organized by CAUL and its Member Institutions.

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Climate Migration: An Impending Global Challenge

For months, we have watched the crisis at the Mexican border as migrants tried to enter the U.S. In March, the U.S. Customs and Border Protection office estimated that there were 171,700 people attempting to cross the border—the highest number in 20 years. About 30 percent were families, of which one third were refused entry under Title 42, a public health statute.

The number of unaccompanied children arriving and being held in custody in U.S. border shelters hit over 5,700 in March. And this week, five unaccompanied girls between the ages of seven and 11 months were found at the Texas-Mexico border. While a migrant surge occurs every year as people come to the U.S. for seasonal work, the record number of children being sent by themselves is likely a sign of desperate conditions back home.

Most of those coming to the U.S. are residents of Guatemala, Honduras, and El Salvador, which are considered some of the most dangerous places on Earth. These countries are poor and plagued by gang violence, extortion, and government corruption.

Last year, they were hard hit by COVID, and then two back-to-back hurricanes in November, which killed more than 200 people. The storms displaced over half a million people, buried houses under mud, and destroyed 40 percent of the corn crop and 65 percent of the beans. Many people lost homes, access to clean water, and their livelihoods. The governments did not offer much help.

Climate change — as embodied by the hurricanes — may have been the precipitating factor that pushed many to try to cross the Mexican border into the U.S., but it is usually one of many reasons that people decide to move.

Alex de Sherbinin, associate director for Science Applications and a senior research scientist at the Earth Institute’s Center for International Earth Science Information Network, said, “Climate change, if it’s not currently the main driver of migration, tends to operate indirectly, and will continue to do that. But as the number of severe and extreme weather events or climate-related disasters increases, we’re going to see more migration and more of that may be directly triggered by it.”

Most ongoing migration occurs in response to fast-onset events, such as extreme weather, and usually results in short-term displacement within the person’s own country. This is naturally easier than migrating to another country, and occurs more than three times as often as international migration. But recurring temporary displacements can often lead to permanent displacement. As climate change impacts intensify and living conditions in certain areas gradually worsen, affecting land productivity, access to clean water, food security, and livelihoods, more and more people will likely be forced to leave their homes and potentially cross borders into other countries.

Climate change and migration

For thousands of years, humans have lived mostly on lands where a limited range of comfortable temperatures enabled an abundance of food to grow. Today, only one percent of the world is barely tolerable due to heat; but by 2070, extremely hot zones could make up almost 20 percent of the land, which means that a third of humanity could potentially be living in uninhabitable conditions. For every degree of temperature increase, it’s estimated that one billion people are pushed out of the hospitable zone.

The impacts of climate change — sea level rise, heat waves, storms, drought, and wildfires — will influence global migration. The New York Times reported that 40.5 million people across the planet were displaced in 2020—the most in 10 years—largely due to these impacts. The 2018 World Bank report Groundswell , which the Earth Institute’s de Sherbinin and Susana Adamo worked on, cited estimates that 30 to 143 million climate migrants may be forced from their homes by climate change impacts by 2050. The Groundswell II report, due out in July and covering all developing countries, pushes the upper bound to more than 200 million.

By 2035, the frequency of major hurricanes is expected increase by 12 percent in the South Indian Ocean, 14 percent in the Atlantic, and 41 percent in the South Pacific compared to 1986-2005 averages. Between now and 2100, sea levels could rise between two and 6.9 feet, submerging millions of homes around the world; sea level rise also creates larger storm surges and can cause saltwater contamination of farmland and drinking water supplies.

Drought has displaced 800,000 within their own countries each year since 2017; in the future, dry regions are expected to get drier still. And over the last decade, wildfires around the world have forced more than 200,000 people per year to leave home; 75 percent of them were in the U.S. Moreover, scientists also believe that there will be more compound weather events , such as flash floods and mud slides that occur after wildfires.

In 2017, approximately 23 million people around the world were displaced due to sudden extreme weather events. Another 44 million or so were displaced due to “humanitarian crises,” likely exacerbated by the cascading effects of climate change. For example, climate experts believe the extreme drought in Syria led to its civil war in 2011. And as crops fail and livelihoods are lost, terrorist groups recruit more desperate people and violence spreads. In countries without the resources to deal with climate change impacts and care for their people, conflicts over resources arise. A recent report by the National Intelligence Council predicted that climate change effects will increase migration, which in turn will put a strain on both origin and destination countries and potentially trigger disputes that could become national security concerns.

Climate migrants of the future

The Groundswell report focused on migration in sub-Saharan Africa, South Asia, and Latin America, which together comprise 55 percent of the developing world’s population. It projected that, if we do not take bold climate action to reduce greenhouse gas emissions and help developing countries, 143 million people from these regions could be forced to move within their own countries to flee the effects of climate change. Migration could also accelerate after 2050 due to stronger climate impacts and population growth. If we can act to stem climate change, the number could be reduced to between 31 and 72 million. Extreme heat events, declining water availability, diminishing snowpack that feeds river basins, and sea level rise will drive people from “hot spots”— such as low-lying cities, coastlines, and places with water scarcity and decreasing crop yields. These migrants will gravitate toward places with a more hospitable climate for agriculture and more job opportunities.

Another study found that higher tides due to sea level rise could affect the land that 150 million people live on by 2050. If the melting of the Antarctic ice sheets picks up speed, 300 million could be affected and up to 480 million by 2100. Seventy percent of the people who would be affected live in eight Asian countries: China, Bangladesh, India, Vietnam, Indonesia, Thailand, the Philippines, and Japan.

Sea level rise has already overtaken eight Pacific islands, forcing the residents to migrate, and two more islands will soon disappear. By 2100, it’s estimated that 48 islands will have been submerged.

Parts of the U.S. are increasingly difficult to live in because of drought, floods, hurricanes, wildfires and sea level rise. A collaborative effort between ProPublica and the New York Times predicted that 162 million Americans will experience a decline in the quality of their environment and by 2070, four million could be living outside of their comfort zone. Because California has experienced record-breaking heat waves and rampant wildfires, with the wildfire season getting longer each year, many Californians are already moving to Idaho, Texas, Oregon and Washington.

Another researcher projected that rising sea levels will force 13 million Americans to move away from the coasts, and that in-land cities such as Atlanta, Orlando, Houston and Austin could each get 250,000 new residents by 2100.

Flooding and high tide are jeopardizing the Quileute Tribe’s school in northwest Washington, forcing the tribe to move the school and tribal government seat 2.5 miles away. In Louisiana, residents of low-lying Isle de Jean Charles are being moved 40 miles to higher ground in the first federally funded U.S. community resettlement project resulting from climate change.

Migration can be considered an adaptation to climate change, as those facing increasingly dire living situations who have the means will likely move. Most people don’t want to leave home, but if they feel they have no choice, they will usually first move from the countryside to a nearby city. If these cities lack the infrastructure or resources to support new residents, they could become overwhelmed.

And migrants with few resources and opportunities often end up living in slums, which are more susceptible to the impacts of climate change and chaos. Today half the global population is urban; the World Bank has estimated that by 2050, 67 percent of humanity will live in cities, with 40 percent of them living in slums by 2030.

Governments in many countries are already reacting to the waves of migrants by holding them in detention centers and erecting walls—Hungary closed off its border with Serbia, India constructed a fence on its Bangladesh border, and under Trump, the U.S. built its own wall. The anti-immigration sentiment has also ushered into office more nationalist governments around the world.

Meanwhile, as the wealthy are able to move to higher or cooler ground or to a more resilient location, some of the most vulnerable people without the means to move—like the poor or elderly—become trapped. This becomes a vicious cycle: As people abandon the community, there is less of a tax base to pay for social services, and those who are left behind and need public support suffer more as they become increasingly desperate. The disparity between rich and poor and their ability or inability to deal with climate change will almost certainly end up creating even more social division than exists now.

Climate migrants have no legal protection

Right now, the world is unprepared to meet the challenge of climate migration. No country offers asylum or legal protection to climate migrants. Because climate change cannot always be identified as the sole or principal reason for migrating, climate migrants have little recourse within current international or U.S. laws. They are not considered “refugees” because they do not fit under the 1951 U.N. Refugee Convention, the U.N.’s legal document that protects refugees—defined as displaced people “who have a well-founded fear of being persecuted because of their race, religion, nationality, membership of a particular social group or political opinion , and are unable or unwilling to seek protection from their home countries.”

While some experts believe climate migrants should be included under the “refugee” rubric, others argue that doing so would water down a convention that is already ignored by many countries. De Sherbinin said, “The fact is that Western governments have shown very little desire or inclination to receive migrants from other parts of the world—refugees—even by current standards, so to broaden the definition, you run the risk that people or governments will just say, ‘I’m opting out,’ or ‘I’m not even going to be part of this convention.’ It may be more appropriate to have this be a matter of national decision-making, so governments can decide whether they want to expand the definitions under which they receive refugees.”

The U.N. High Commissioner for Refugees does provide relief help and planned relocation guidance to the “disaster displaced,” and in 2019, appointed a special advisor to help shape the agency’s climate change agenda.

The Global Compact for Safe, Orderly and Regular Migration , an agreement adopted in 2018 by 164 countries, but not the U.S., helps countries prevent displacement due to climate change and provide support to those who are forced to migrate. It is the first international agreement to clarify how countries should deal with international migration, but it is not legally binding.

Because there is no organization that oversees migration, displaced people go wherever they can and not necessarily where it would be best for them to go. As climate migration increases, the situation will likely become more chaotic and overwhelming unless legal and social frameworks are created for the displaced. However, given the current nationalistic and anti-immigrant atmosphere, trying to create an international legal framework to protect climate migrants might actually lead to reducing refugee protections, not extending them.

There are no easy solutions

While there are no easy answers to the complex challenge of climate migration, here are some ideas that have been proposed to make it less chaotic and more humanitarian.

-Enable free movement between member states. For example, the Caribbean has Free Movement Agreements for climate migration. During the 2017 hurricane season, the governments allowed displaced people to move to other islands, waived the need for travel documents and work permits, granted indefinite stays to the displaced, and helped with resettlement.

-Create a Western Hemisphere regional compact on permanent displacement to expand protection and status for those who have been permanently displaced over an international border by climate change impacts.

-Plan relocation of villages and communities from areas where climate change impacts are threatening. In the Pacific Islands, Vanuatu has developed safeguards and operating procedures for relocation which include technical expertise and financial assistance.

-Ensure that cities are better able to deal with an influx of migrants through investments in infrastructure, sanitation and health services, education, and opportunities for skills and job training.

-Fund more research on how climate change will shape migration so that governments can better predict migration and prepare for it.

-Set up a system of criteria and proof to determine if someone has a credible claim that they were harmed by climate impacts, since this is necessary for the application of laws and rules.

-Build climate migration into policies and long-term planning. This would include helping communities stay where they are by investing in resilience, job opportunities, education and social safety nets. For climate migrants, create incentives to move to low-risk, high-opportunity places. For example, Bangladesh is creating “climate-resilient, migrant-friendly” towns to encourage migrants to move to secondary cities rather than to already overcrowded major cities.

-Pay climate reparations. “The historically largest emitters owe something to the countries that are now being impacted most heavily by climate impacts,” said de Sherbinin. “And providing them with assistance is no longer just a matter of giving handouts—it’s actually an obligation. Because we [wealthy countries] set up the whole climate problem [through our emissions] for many of these countries that have contributed so little to it.”

What President Biden is doing

In an attempt to address the factors that make people want to enter the U.S., President Biden has proposed $4 billion in aid to help Honduras, El Salvador and Guatemala deal with poverty, lack of jobs, government corruption, violence and climate change. He has also announced $310 million of emergency funding to help displaced people. These measures, however, could paradoxically increase migration by giving more people the means to move.

Biden has also issued an executive order for the creation of a report on climate change and migration, with recommendations for the resettlement and protection of migrants. The mayors of 15 cities, including New York, Los Angeles, Chicago, Houston and others, have asked to be consulted for the report, as they “deal with the impacts of climate change and migration on a daily basis.” De Sherbinin is also part of an expert group organized by Refugees International to advise the Biden administration on shaping policies for climate migration.

Under Trump, the number of refugees allowed into the U.S. was set at an historic low of 15,000. President Biden has now raised the refugee cap to 62,500, and plans to increase it to 125,000 in 2022. A number of Republicans criticized the decision as irresponsible and dangerous.

“People in the U.S. perceive that migrants are a burden,” said de Sherbinin. “The reality is the data just don’t prove that in any way. Look at migrants who pay taxes—I’m talking about the undocumented—who are working hard contributing to society. They’re not on welfare, they don’t even qualify for welfare. They’re the ultimate ‘sink or swim’ people who are going to have to pull their own weight. Definitely, there’s a need to recognize and dispel some of the myths about migrants being parasites. But I think, frankly, most of the fear and concern is borne out of a racist reaction to people who are Brown and Black and other colors, and don’t speak our language. They are perceived as a threat.”

The U.S. could actually stand to benefit from an influx of immigrants because it, like other industrialized countries, is facing a demographic decline, which could lead to slow growth and a weakening economy. Migrants who come to the U.S. for better job opportunities would stimulate economic growth through their labor, their buying power and the taxes they pay.

ProPublica and the New York Times modeled international climate migration, as well as political responses to climate change and migration. It showed that how leaders respond to climate change and migration will make a huge difference in how much human suffering there will ultimately be. If they fight climate change aggressively, manage migration humanely, and invest in resiliency, there will be less poverty, less migration, and enough to eat, and these outcomes could help the world be a more stable and peaceful place.

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Climate Impacts as Drivers of Migration

Explore the Issue

Global climate patterns have changed over the last century, triggering more extreme weather events including hurricanes, heat waves, and droughts. Looking forward, the Intergovernmental Panel on Climate Change (IPCC) has projected that, at the current rate, global temperatures are likely to average 1.5°C above pre-industrial levels at some point between 2030 and 2052. Even this seemingly modest increase, which is well within the range of daily variability, will result in cascading impacts on ice sheets, ecosystems, and productive systems that will fundamentally alter habitability when spread over the entire land surface of the planet. The effects will not be spread evenly, and already high latitudes are warming at twice the rate of the rest of the world while drylands are expanding.

Climate can be seen as the envelope in which all economic activities take place, and these changes could spell significant disruptions for modern society, both in low- and high-income settings. Yet humans have the ability to adapt as well as free will, so one must be careful not to engage in a sort of environmental determinism that draws a direct line from projected climate changes to future migration. Instead, climatic circumstances exist as one of several factors that drive the decision by an individual or community to migrate, and may compound those other drivers or be mitigated through policy action or individual circumstance.

This article draws on a growing evidence base for contemporary environmentally induced migration that includes individual case studies, sophisticated statistical analysis, modeling work, and the UK government’s benchmark 2011 Foresight report, Migration and Global Environmental Change . It summarizes key lessons from the evidence and assesses the implications for future migration under climate change.

Listen to a Podcast Discussion with Alex de Sherbinin

General Observations

The question of how climate factors influence migration is fraught with so many contextual specificities that it is helpful to begin with a clarification of terms as well as some general observations. On the migration side, researchers for more than a century have uncovered a range of so-called “stylized facts” governing how, why, and under what circumstances people move. Push and pull factors in origin and destination areas produce migration streams and counter-streams; at the same time, intervening obstacles such as costs of travel and border controls inhibit migration. Human movement tends to increase over time, and migrants are more likely to move to places where relatives or friends have preceded them. Migration is selective, meaning that, depending on the context, some people—such as those who are younger or males—are more likely to move than others. Finally, economic motives tend to dominate. Environmental factors can influence all these elements.

Mobility Frameworks

The three dimensions of migration are space, in terms of the distance migrants travel or the borders they cross; the duration of their stay; and volition of their movement, on a spectrum from fully voluntary to forced. In terms of volition, environmental migration is generally understood to fall on the forced end of the spectrum (see Figure 1). For this reason, terms often associated with climate migration include climate displacement, mass migration, distress migration, and climate refugees—a popular but problematic term, since “refugee” is a legal category limited to people fleeing persecution owing to factors such as their race, ethnicity, creed, or political beliefs.

Figure 1. The Mobility Continuum, from Forced to Non-Forced Movement

Source: Susana Adamo and Alex de Sherbinin, “Climate Change and Migration” (Presentation at CARE climate briefing, February 11, 2009, Washington, DC).

Even at the forced end of the spectrum, a migrant’s volition is worth considering. The aspirations and capabilities theory of migration recognizes that people move because they aspire to a better life than the one they have in their place of origin, and that their ability to act on that aspiration is highly contingent on their various individual and household capitals, including social, human, physical, natural, and financial ones, as well as legal and other barriers. Thus, a number of circumstances are possible: one may desire to migrate but lack the ability; one may desire to stay in place but nevertheless be forced to leave due to a natural disaster, conflict, or government intervention; or one may either desire to migrate or not, and be assisted or required to do so by a government in a process called planned relocation or resettlement.

Beyond voluntary and forced, there are a range of other mobility types, making it challenging to speak of migration in general terms. Domestic or internal migration requires different resources—including financial resources as well as human and social capital—and often has lower barriers than international migration. For this reason, the volume of regular internal migration is estimated to be at least three times larger than international migration. The rate of internal migration is probably even higher, yet data deficiencies make it difficult to know for sure. Even within domestic migration, there are differences in characteristics for people going from rural to urban areas, from one rural area to another, from an urban center to rural periphery, and between urban centers.

Permanent or long-term migration may be the most popular image of migration, but in many regions short-term, circular, or seasonal patterns of mobility predominate, especially for people such as migrant laborers and nomadic pastoralists. Finally, there are often distinct differences in migratory patterns between developed and developing countries.

Climate Hazards

In terms of the way that climate factors influence migration, risk frameworks such as the one introduced by the IPCC are helpful for understanding how climate hazards intersect with social vulnerability. Climate hazards can be classified by the location, timing, duration, and intensity of events. Social vulnerability is a function of the population’s sociodemographic characteristics such as age, sex, ethnicity, race, education, and major livelihoods, as well as its access to financial and other capitals and adaptive capacity. In general, greater frequency and intensity of climate hazards are more likely to prompt people to migrate when the population is more vulnerable and has a lower capacity to adapt.

Climate events can be divided into fast- and slow-onset events. Fast-onset events include climate extremes such as floods, storms, heat waves, and drought. Slow-onset events are gradual changes to climate regimes—such as increased temperatures or longer-term rainfall variation. Other slow-onset events include sea-level rise, ocean acidification, glacial retreat and related impacts, soil salinization, land and forest degradation, loss of biodiversity, and desertification. Each has a more or less direct relationship to climate change. Evidence suggests that fast-onset events are more likely to result in short-term displacement followed by a return to source areas, whereas slow-onset events are more likely to drive permanent migration. However, successive fast-onset events can reduce household assets in ways that may encourage long-term migration.

The Foresight report suggests that environmental (including climatic) factors may occasionally have direct impacts on population movements, but are more likely to operate through intermediate drivers, namely economic, social, demographic, and political ones (see Figure 2). Household characteristics and intervening obstacles can also influence the decision to migrate. A major contribution of the Foresight project was to emphasize that environmental factors rarely act in isolation, but rather exist as part of a broader constellation of macro-, meso-, and micro-level drivers.

Figure 2. Environmental Drivers of Migration Decision-Making

Source: Foresight, Migration and Global Environmental Change (London: The Government Office for Science, 2011), available online .

Another concept put forward by the Foresight project was that of “trapped populations,” which stay in place despite worsening conditions and a desire to move. At the low end of the income spectrum, people may lack the resources to move despite wanting to do so. Even the cost of bus fare or the prospect of leaving one’s local support network may represent a barrier to moving. Research from Manuela Angelucci, for instance, shows that offering poor families small cash payments can increase a family’s propensity to send at least one member away in order to diversify household income. Meanwhile, at the high end of the income spectrum, people have fewer incentives to migrate and are more likely to be “moored” in place. Migration is more likely for those in the middle of the wealth and capabilities spectrum, as confirmed by the United Nations Development Program’s Scaling Fences report.

Climate Migration in Developing Countries

Researchers investigating the linkages between climate change and migration in developing countries often speak of migration—whether international or domestic, or responding to slow-onset or multiple rapid-onset events—as one of a number of forms of adaptation. In this context, migration serves several purposes.

First, migration to less risky or more stable environments can reduce individual or household exposure to climate hazards such as recurrent droughts hampering agricultural yields or floods inundating coastal areas. Second, at a household level, migration of one or more individuals can be part of a livelihood-diversification and risk-reduction strategy, whereby remittances from household members in destination areas offer the household some financial stability when hazards occur and choke off other income streams. Third, migration can increase household assets and thereby resilience to climate change. Fourth, migration can reduce the number of mouths to feed in a household, especially during the dry or lean season in agricultural regions, thereby increasing food security for those who remain behind. Lastly, returning migrants can bring new skills and technologies back to the communities they left, increasing their wealth and resilience to climate hazards.

A large and growing body of research has investigated the relative influence of climate factors in instigating migration. These range from anthropological case studies and survey research on climate perceptions and migration to statistical analyses based on census or survey data that control for factors known to influence migration and then introduce climate factors to determine their relative effect. Much of the large and growing body of research in this field focuses on the so-called “agricultural pathway,” by which the impact of climate on migration is moderated by changes in agricultural productivity. Analyses of this type in parts of Africa, South Asia, and Latin America show that increased or extreme temperatures and rainfall variability and extremes can negatively affect crop yields in ways that may induce migration. Yet the emigration may be limited in terms of who migrates, from which areas, and to which destinations. In one statistical study in Mexico, Raphael J. Nawrotzki et al. found that longer droughts and periods of anomalously high temperatures increased the propensity for rural-urban migration yet had relatively little impact on other forms of migration.

While these statistical analyses have sometimes found strong correlations between climate anomalies and migration, their effects vary from place to place, suggesting that economic drivers, policy, and cultural factors, such as migration as a rite of passage to manhood, still dominate migration decision-making. Some have argued that climate factors—much like the COVID-19 pandemic—merely expose underlying vulnerabilities and fractures in society. In other words, absent fundamental inequities and systems biased against smallholder agriculturalists or other vulnerable populations, they would not have an impetus to move. Climate factors simply tip the scales slightly in favor of migration. Jesse Ribot et al. found that narratives of impending climatic changes themselves, quite apart from actual experienced impacts, have engendered anxiety regarding the future potential for productive livelihoods in rural Senegal.

The agricultural pathway remains the most studied in terms of climate-migration linkages, but research has also been conducted on pastoralist livelihood systems, in coastal areas in relation to sea-level rise, in forest regions, and in urban areas. Findings similarly vary and are sometimes counterintuitive. For example, in pastoralist systems, climate “displacement” may in fact mean that nomadic herders become less mobile owing to the loss of livestock. Furthermore, many low-lying delta regions remain popular migration destination areas despite their exposure to storms and sea-level rise.

Climate Migration in Developed Countries

Most of the research focus on climate migration has occurred in developing countries, but there is emerging work in developed countries. One reason there has been less focus in developed countries is that their populations are highly urbanized and people’s incomes and livelihoods are less dependent on local environmental conditions owing to extended and international supply chains. In fact, modeling conducted by the author’s center for the Foresight project found high levels of net migration into climate-sensitive dryland and mountain ecosystems in North America over the past four decades, whereas similar ecosystems in all regions of the developing world experienced massive outmigration during the same period.

That said, there is growing interest among scholars in managed retreat from climate-exposed areas, especially coastal zones, as well as fire-prone forest areas and flood-prone riparian environments in developed countries. Research in this area is focused on the mechanics of home buyouts, engineering solutions, environmental justice, understanding local planning needs, and how best to modify existing government policies such as the U.S. National Flood Insurance Program. Thus far, evidence does not suggest that there is wholesale migration out of the near-coastal or fire-risk zones. On the contrary, at least in the United States, these areas generally have seen above-average population growth as so-called “amenity migrants” move to the coast and into the urban-wildland interface. This has occurred despite high-profile natural disasters such as Hurricane Sandy in 2012 and major wildfires in California in 2019 and 2020, among many others. But that may begin to change.

Future Projections and Prospects

This article has provided an overview of the major strands of research on climate change-induced migration. Returning to the question posed at the beginning, how likely is it that we will witness mass migration as result of climate change in coming decades?

Researchers have used a variety of techniques to try and predict numbers of future migrants and, to some degree, source and destination areas. At the simplest level, exposure models identify the number of people who will likely be exposed to a given hazard—most often sea-level rise, but also recurrent flooding or drought—and estimate the proportion of people likely to move. For example, researchers Scott Kulp and Benjamin Strauss estimate that 1 billion people now occupy land less than 10 meters above current high-tide lines, including 230 million below one meter who will presumably need to relocate as sea levels rise. At a more sophisticated level, statistical models of populations’ past tendencies to migrate in response to climate anomalies project possible numbers of migrants under various future scenarios. Newer modeling approaches include agent-based models (ABM), system dynamics, radiation models, and population gravity models. A gravity model developed by the author and colleagues for the World Bank’s Groundswell report finds that by 2050 the world could see 143 million internal climate migrants in Latin America, East Africa, and South Asia alone. Each modeling method has its strengths and weaknesses, and not all can be easily applied in all contexts.

A critical assumption of many models is that the impacts of climate change will progress along a more or less smooth arc, with no major tipping points or thresholds that flip the climate system—and in turn the agricultural, economic, and other systems—onto new and less predictable pathways. This could be a limitation if the future does not play out as predicted. At broader spatial scales, these models also do not adequately account for various possible political upheavals, conflicts, or pandemics which could intersect with climate impacts to add unexpected shocks to existing systems. This is one reason why “resilience” has become a term of art among scholars; resilience-building will be critical for societies to navigate the various emerging challenges in this century.

To conclude, climate change and variability are already affecting mobility of all types, including longer-term migration. As with all migration, most climate migration and displacement will be internal, though even the relatively small international fraction could be sizeable given growing populations and the potential scale of climate impacts. People migrate for a variety of reasons, with economic factors predominating. But in cases of large-scale migration, concerns about local safety and security along with a prevailing hopelessness seem to be driving increasingly perilous journeys.

In this sense, it is a misnomer to speak of “climate migrants” as a distinct group of people forced to move solely because of climate factors. Perhaps this label is appropriate for a few migrants from low-lying areas and small island states, but in many areas climate factors could be better characterized as an additional nudge out of marginal environments for people who also have other reasons to leave. In some regions, people are fleeing increasingly desperate situations and mobility is one of the few forms of personal agency available to them. In others, a perception that climate change will make life more difficult in the future, combined with a desire for a better life, prompts them to move for their own sake or that of their children.

In all of this, it is important to note that society and institutions are ill-prepared to meet the coming challenge. Legal instruments such as the 1951 Refugee Convention set narrow criteria for protection, for example requiring that an individual fear persecution, effectively excluding those who would nevertheless truly suffer if forced to return to their home countries. Donors are increasingly devising programs to promote in situ adaptation strategies, some of which are designed to reduce outmigration from rural areas, as well as migrant-centered interventions. Some are designed to facilitate the integration of migrants into urban environments or host countries, while others seek to repatriate migrants from developed countries, in some cases providing them with job training and financial assistance. Programs to limit migration generally have had a spotty record of success in achieving their desired aims. In fact, one of the byproducts of development is greater freedom of choice; where people are able to fully realize their aspirations and exercise their capabilities they often choose to move. This will be no less the case in a world transformed by increasingly severe climate impacts.

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SYSTEMATIC REVIEW article

Migration theory in climate mobility research.

$\nAlex de Sherbinin$

1 Center for International Earth Science Information Network (CIESIN), Columbia Climate School, Columbia University, Palisades, NY, United States
2 Department of Geography, Environment and Society, University of Minnesota, Minneapolis, MN, United States
3 Department of Environmental Studies, New York University, New York, NY, United States
4 United Nations University Institute for Environment and Human Security (UNU-EHS), Bonn, Germany
5 Center for Climate Systems Research (CCSR), Columbia Climate School, New York, NY, United States
6 Department of Earth and the Environment, Boston University, Boston, MA, United States

The purpose of this article is to explore how migration theory is invoked in empirical studies of climate-related migration, and to provide suggestions for engagement with theory in the emerging field of climate mobility. Theory is critical for understanding processes we observe in social-ecological systems because it points to a specific locus of attention for research, shapes research questions, guides quantitative model development, influences what researchers find, and ultimately informs policies and programs. Research into climate mobility has grown out of early studies on environmental migration, and has often developed in isolation from broader theoretical developments in the migration research community. As such, there is a risk that the work may be inadequately informed by the rich corpus of theory that has contributed to our understanding of who migrates; why they migrate; the types of mobility they employ; what sustains migration streams; and why they choose certain destinations over others. On the other hand, there are ways in which climate and broader environment migration research is enriching the conceptual frameworks being employed to understand migration, particularly forced migration. This paper draws on a review of 75 empirical studies and modeling efforts conducted by researchers from a diversity of disciplines, covering various regions, and using a variety of data sources and methods to assess how they used theory in their research. The goal is to suggest ways forward for engagement with migration theory in this large and growing research domain.

Introduction

The literature on climate migration, or what is now increasingly termed “climate mobilities” ( Boas et al., 2019 ; Cundill et al., 2021 ), has grown considerably since the 2000s ( Piguet, 2021 ; Šedová et al., 2021 ) and owes its origins to work on environmental migration ( Warner et al., 2010 ; Morrissey, 2012 )—a corpus that arose in isolation from the broader migration literature ( Hunter, 2005 ; Piguet, 2018 ). There have been several recent reviews of the evidence for climate impacts on migration ( Borderon et al., 2019 ; Hoffmann et al., 2020 ; Šedová et al., 2021 ; Selby and Daoust, 2021 ), and much has been written on the legal and conceptual ambiguities of terminology around climate migrants and “refugees” ( McAdam, 2012 ; de Sherbinin, 2020 ; Mayer, 2020 ), the terminological difficulties associated with different types of mobility from voluntary to forced ( Avis, 2017 ; Piguet, 2018 ), and the apolitical and ahistorical nature of the climate migration literature ( Morrissey, 2012 ; Ribot et al., 2020 ). Yet, with the exception of a few authors who give the subject limited or case-specific treatment ( Hunter, 2005 ; Hugo, 2011 ; Hochleithner and Exner, 2018 ; Piguet, 2018 ; Kaczan and Orgill-Meyer, 2020 ; Zickgraf, 2021 ), there has been insufficient focus on how researchers studying climate migration engage with theory. On the other hand, consensus is growing that there is a need to embed climate mobility research in migration theory ( Doevenspeck, 2011 ; Freeman, 2017 ), that environmental factors have a place in migration theory, and that the climate mobility research community has much to contribute to theory-building ( Hunter and Simon, 2022 ).

Theory 1 matters in empirical climate migration research because theories are formulated to elucidate causal linkages and to explain, predict, and understand phenomena. Theory is critical to the sciences, since it points to a specific locus of attention for research, shapes research questions, guides quantitative model development, and ultimately informs policies and programs. It is a vital part of “sense making” in the social sciences and, as with data and methods, continues to evolve as part of scientific advancement. However, empirical climate migration research is often critiqued because it insufficiently engages with theory, leading some to write-off the contributions as overly simplistic and environmentally deterministic ( Morrissey, 2012 ). The “environmental refugees” framing prevalent in the literature of the 1990s and early 2000s is a case in point ( Myers, 1993 ; Barrios et al., 2006 ). The use of theory within this framing minimized the role of the individual's abilities to make decisions within a given context shaped by conditions of the time and place. Ultimately, migrant volition was minimized, demographic and contextual factors were often overlooked, and environmental and structural factors were presented as preeminent. The disconnect between climate (and environmental) migration research and evolving migration theory has limited the development of an important body of empirical scholarship.

Given the varied disciplinary backgrounds of climate migration researchers—from geography, economics, and demography to environmental and computer science—the opportunities to engage deeply with migration theory are often overlooked in favor of focusing on data and methods ( Hoffmann et al., 2021 ). What results is that researchers employ complex analysis approaches within a fairly simplistic push-pull model or ready-made conceptual frameworks from the environmental migration literature. These data- and methods-focused approaches miss opportunities to advance theory. Empirical case studies provide a unique opportunity to refine and refute theoretical perspectives to ensure that the way researchers and policy-makers fundamentally understand the migration experience continues to develop. The rapidly growing body of empirical literature exploring climate migration conducted by scholars from a wide range of disciplines provides a diversity of perspectives on this complex topic that can help to advance migration theory in important ways. However, by focusing on often complex models and data analytic approaches, scholars may miss these opportunities to contribute to theoretical advances.

The purpose of this article is three-fold: to explore how migration theory is invoked in empirical studies of climate-related migration; to provide suggestions for engagement with theory in the emerging field of climate mobility; and to explore how climate mobility researchers can contribute to migration theory building. In the sections that follow, we first provide a review of migration and other theories that are frequently cited in the climate migration literature (section Brief Review of Migration Theory). Then we examine a selection of recent empirical literature originating from different disciplinary perspectives that engages with theory in different ways (section How Theory Is Employed in the Empirical Literature). Using these 75 empirical climate migration studies conducted from 2010 to the present, we characterize the theoretical framings across the sample to better understand how this corpus of research draws upon theory to advance climate migration science, and then, in section The Way Forward, we use these findings as a springboard to suggest paths forward for advancing theoretical perspectives in meaningful ways in the new field of climate mobilities. The goal is to improve empirical work in the field while ensuring that this work, in turn, helps to advance wider migration theory. In section Conclusion, we provide some brief conclusions and reflect on connections between theory and policy.

Brief Review of Migration Theory

According to King (2012 , p. 28), “Explicitly or implicitly, the interplay between the agency of the individual actor and the structural context within which that actor maneuvers is at the heart of most studies of migration.” Bakewell (2010) and De Haas (2021) have both criticized the agency vs. structure dualism in the literature, arguing for more holistic approaches—on the one hand, critical realist approaches, and on the other, the aspirations and capabilities framework. While recognizing that it is not either/or but in many cases both/and, there is limited evidence in the climate mobilities literature that authors are aware of this debate. In this section, we list the theories used to code the sample of empirical studies, beginning with those theories that focus more on individual actors (functionalist theories), and proceeding to structural theories and theories of sustained migration, and end the section by addressing more eclectic perspectives. We also briefly describe how environmental factors have been or could be incorporated into each theory 2 .

It is worth noting that we do not draw strong distinctions between terms such as theory, theoretical frameworks, or conceptual frameworks. It has been suggested that some “theories” are actually little more than empirical generalizations or stylized facts (e.g., push-pull or migration hump). A further discussion of these distinctions can be found in Carling et al. (2020) . In our view, frameworks are a graphical representation of theory, illustrating causal linkages through diagrams 3 . Thus, we intentionally are inclusive, using theory as an umbrella term for the purposes of this study.

Neoclassical Migration Theory

This theory focuses mainly on differences in wages and employment conditions between countries/regions and the costs of migration. According to neoclassical migration theory, as wage differentials decline, migration should slow down or stop ( Lewis, 1954 ; Massey et al., 1993 ) 4 . Migration is an individual decision to maximize profits through a process of weighing costs and benefits. Environmental factors can be said to affect wages indirectly, through impacts on rural livelihoods or urban wage rates (see recent work by Mueller et al., 2020 ), where wages may be construed as income from livelihoods that are sensitive to climate variability and change. Generally neoclassical migration theory focuses on wages, but when expanded it can incorporate any form of utility-maximization. For example, environmental amenities might figure into personal preferences that drive migratory responses ( Gosnell and Abrams, 2011 ).

Push-Pull Theory

Push-pull is often grouped with neoclassical migration theory, and according to some scholars represents more of an overarching framework or a descriptive post-hoc model ( Hochleithner and Exner, 2018 ). Push-pull theory frames migration in terms of negative (push) factors in the place of origin that drive people to move away (such as low wages, poverty, lack of opportunities, weather), combined with a number of positive (pull) factors that attract migrants to a new destination (such as higher wages, social services, family members, shared cultural values). This theory distinguishes between push and pull factors, and intervening obstacles that can impede migration (such as costs to move and legal barriers; Lee, 1966 ). Network forces, like the existence of kin or social connections, assist in the move, broadly serving as pull factors. A corollary is that not all people move, and thus the concept of mooring suggests that non-migrants are able to maximize their physical, psychological, and emotional well-being by staying in place ( Moon, 1995 ), an idea that Adams and Kay (2019) relate to a psychological propensity to migrate related to place attachment and other factors. Van Hear et al. (2018) propose a “push-pull plus” model, which distinguishes among predisposing, proximate, precipitating, and mediating drivers that vary in importance depending on the context.

Push-pull theory is very amenable to the case of environmentally induced migration, and indeed underlies some recent population gravity modeling efforts (e.g., McKee et al., 2015 ; Rigaud et al., 2018 ) and also informs the Foresight framework described below ( Black et al., 2011 ). Environmental conditions can affect both push or pull factors—e.g., drought in sending areas could push migrants, while more favorable environmental conditions could act as a pull factor, as Van der Geest (2011) found in Ghana. Van Hear et al. (2009) argue that several factors may be operational in any migration flow, and the challenge is to identify which combinations are most important, and which are policy-mutable. It is the search for the relative influence of climate factors that preoccupies much empirical research reviewed here—a pursuit that some see as increasingly irrelevant ( Cundill et al., 2021 ).

New Economics of Labor Migration (NELM)

NELM situates migration decision making in households. Individuals move to support the larger family/economic unit, either voluntarily or at the behest of the household head or community members ( Stark and Bloom, 1985 ). People act collectively not only to maximize expected income, but also maximize status within an embedded hierarchy, to overcome barriers to capital and credit, and to minimize risk and diversify the incomes ( Massey, 2001 ). NELM both accounts for wage differentials and failures in insurance, credit and savings markets that mean households have to self-insure. NELM is consistent with various forms of environmental migration. For example, seasonal migration in the Sahel, which is fundamentally shaped by environmental characteristics and constraints, can be said to conform to NELM since it is often a household decision, it serves to diversify income streams, and it reduces pressure on household food stocks ( van der Land et al., 2018 ). NELM also fits well within the risk framing of the Intergovernmental Panel on Climate Change, insofar as it conceives of migration as a risk reduction strategy and a means of adaptation ( McLeman et al., 2021 ).

Mobility Transition Theory/Migration Hump

Originally developed by Zelinsky (1971) , the original transition theory followed the literature on modernization ( Rostow, 1959 ) and demographic transition ( Caldwell, 1976 ), in which migration is limited in pre-modern societies, then picks up in an early transitional society with mass rural-urban migration. Furthermore, the theory holds that socioeconomic development creates economic imbalances between regions, which is corrected for through migration ( Fussell, 2012 ). Hochleithner and Exner (2018) suggest that the mobility transition is one of the most empirically confirmed theories of migration, and De Haas (2011) states that it best explains migration patterns within the Mediterranean basin. Migration Hump , a related but different theory, hypothesizes that there is an international migration “hump” as incomes rise with the development process, and that in time as a country becomes more prosperous, the level of international migration drops ( Martin-Shields et al., 2017 ) 5 . It helps explain an apparent paradox, which is that migration levels actually increase as income levels increase in low-income settings. From a climate migration perspective, it could be argued that some measures that promote in situ adaptation may actually result in an increase in migration levels as local incomes rise ( Stojanov et al., 2021 ).

Historical-Structural Theories

This category broadly includes macroscale theories such as World Systems, Dependency Theory, Structuration Theory, Dual Labor Market, and the New International Division of Labor. These theories put the emphasis less on individual decision making, and more on structural economic factors that explain migration, particularly from lower income countries to higher income countries, but also from rural to urban areas. We describe a few examples. World Systems theory, defined by Wallerstein (1976) , is based on an unbalanced world economic order, which is divided into core-states and peripheral areas. Often the peripheral areas have a low degree of autonomy—and/or face a neo-colonial situation. The theory suggests that migration flows are motivated by the unequal distribution of wealth between the rich core and the poor periphery. In this view, international migration is influenced by historically formed macro-structural forces, and is inherently exploitative and self-perpetuating as it leads to underdevelopment in migrant source areas ( King, 2012 ). This has similarities to the Dual Labor Market theory ( Massey et al., 1993 ), which posits that international migration stems from the labor demands of modern industrial societies. Structuration theory represents a hybrid between structural approaches and those recognizing personal agency. The idea is that society shapes individuals and, in turn, individuals shape society in the ongoing process of change. As applied to migration, it suggests that higher-level structural factors set limits on migration possibilities, but that at local levels people interact with their situations and may choose to migrate, which shapes both the local situations and, over time, higher-level structures ( Giddens, 1984 ; Morawska, 2007 ; King, 2012 ) 6 .

Many of these theories focus on global inequalities, which parallels discussion in the climate justice literature. In regard to migration, the climate migration literature posits that the wealthy nations that contribute most to greenhouse gas emissions are now conveniently promoting “migration as adaptation,” essentially leaving it to poor people to circumstances they did not create, while simultaneously closing borders ( Bettini and Gioli, 2015 ; Gonzalez, 2020 ). Political economy perspectives may be considered a subset of historical-structural theories. For example, in studies in West Africa, Carr (2005) and Ribot et al. (2020) found that power imbalances and structural factors deprive populations of access to resources and opportunities to prosper in place, thus contributing to migration.

Environmental Migration Frameworks

These are conceptual diagrams that draw on the aforementioned theories to identify causal pathways through which environmental change may induce migration flows. The most prominent is the Foresight framework ( Foresight, 2011 ), which incorporates a number of the elements of other theories, including neoclassical theory, migrant selectivity, world systems, and push-pull. Important in the Foresight framing is that climate change is, at most, an indirect driver of migration which operates on the direct drivers—namely the pre-existing economic, demographic, social, political, and environmental conditions. Importantly, the Foresight report was one of the first to explicitly recognize “migration as adaptation” ( Tacoli, 2009 ), framing it as an important policy response to the observed and projected impacts of climate and environmental drivers on migration.

Forced Migration Theory

While there is no theory of forced migration or displacement ( Piguet, 2018 ), there are empirical generalities ( Castles, 2003 ), and there are growing theoretical explorations of both forced migration and immobility. Human mobility occurs on a continuum from voluntary migration to forced displacement ( Hunter, 2005 ), where displacement tends to emphasize “push” more than “pull” factors. In a risk framework, displacement is a function of the likelihood, severity and nature of the hazard, the exposure of people, and pre-existing vulnerabilities [( Internal Displacement Monitoring Center (IDMC), 2015 )]. In circumstances of displacement, both staying and leaving carry high risks to personal safety, and thus decisions are made in the context of high risk and high uncertainty ( World Bank, 2017 ). What is clear is that those who are displaced often face needs that are far more acute than other migrants—including landlessness, joblessness, homelessness, marginalization, food insecurity, and increased morbidity and mortality. Thus, the movement occurs over shorter time scales as the intensity of the “push” factors are generally higher than in other migration circumstances. As Erdal and Oeppen (2018 , p. 985) point out, “[A] starting point for understanding volition in migration is the range and quality of alternatives available to potential migrants if they just stay where they are. In other words, to what extent will they be able to enjoy a reasonable quality of life without migrating? We might consider the migration less voluntary when the answer is ‘not at all' rather than ‘to some extent.' The perception of suitable options and necessity of alternatives—and the notion of a ‘reasonable quality of life'—are subjective.” We return to theories of forced migration in our discussion of the way forward (section The Way Forward).

Theories Addressing Sustained Migration

This category broadly includes theories such as Network Theory, Institutional Theory, Cumulative Causation, and Migration Systems. These theories do not seek to address how a particular migration flow began, but rather how they grow and are sustained over time. Under Network theory, networks tie migrants, former-migrants and non-migrants in source and destination areas in webs of kinship, friendship and shared origin ( Massey et al., 1993 ; King, 2012 ). They increase the chance of international migration because they lower the costs of migration and provide valuable information to potential migrants, which lowers uncertainty levels. Networks contribute to transnationalism, whereby migrants retain strong connections to source areas ( Portes, 1999 ). Under Institutional theory, “Once international migration has begun, private institutions and voluntary organizations arise to satisfy the demand created by an imbalance between the large number of people who seek entry into capital-rich countries and the limited number of immigrant visas these countries typically offer” ( Massey et al., 1993 , p. 450). This includes migrant smuggling networks. Cumulative Causation theory posits that each act of migration changes the local social context in which potential migrants make decisions to migrate, for example through the distribution of income, the distribution of land, the organization of agriculture, and culture, among other things, resulting in a culture of migration ( Massey et al., 1993 ). This could lead to social tipping points, where the social and economic viability of migration source areas is undercut ( Horton et al., 2021 ). Migration Systems is more of a generalization than a theory. It suggests that international migration flows become stable and continue over space and time, with dyads of sending and receiving countries characterized by relatively intense exchanges of goods, capital, and people ( Mabogunje, 1970 ; Massey et al., 1993 ). Feedback loops develop that draw new migrants into the flow; for example, diaspora communities develop that share information and resources, facilitating new migration ( Fussell, 2012 ). World Systems is sometimes included in this category of theories, since long standing flows are often the result of colonial ties.

According to King (2012 , p. 20),

“The attraction of a system approach is that it enables the conceptualization of migration to move beyond a linear, unidirectional, push-pull movement to an emphasis on migration as circular, multi-causal and interdependent, with the effects of change in one part of the system being traceable through the rest of the system ( Faist, 1997 , p. 193). Hence systems can be self-feeding (like chain migration), self-regulating (correcting themselves in response to a ‘shock' to the system) or self-modifying (e.g., shifting to a different destination when one is blocked off).”

From a climate migration perspective, one aspect of this strand of research is that it shifts the lens from climate impacts on migration decision making in sending areas to climate impacts in both sending and receiving areas, or from hotspots to “hot systems” ( McDevitt, 2009 ). Doevenspeck (2011 , p. e64) adopted cumulative causation as a theoretical framing in a study of rural-to-rural environmental migration in Benin, since it accounted for why migration continues without major differences in wages owing to strong translocal connections between migrants and sending communities.

Aspirations and Capabilities

Sitting somewhere between functionalist and structuralist theories, a more recent theory sees migration decision making as the result of migrant's aspirations and capabilities ( Carling, 2002 ; De Haas, 2010 , 2021 ). While the primary focus is on personal agency, with migration propensity being a function of aspirations (i.e., life goals, desires, and perceptions related to the costs and benefits of the decision to migrate), structural factors enter in through the migrant's capabilities (i.e., education, skills, financial resources, legal constraints, disability), which enable or limit an individual to act on their aspirations. The theory purports to better explain why some people migrate but others do not ( Carling and Schewel, 2018 ). In developing this theory, De Haas (2010) seeks to avoid the ecological fallacy that confounds macro-level migration determinants (e.g., population growth, demographic transitions, development levels, environmental degradation, and climate change) with individual migration motives 7 . While there may be a correlation between these factors and migration levels and transitions, people do not migrate because of them, but rather because they aspire to a better life and they have the capability to act on those aspirations.

Environmental amenities and risks may be among the factors that affect aspirations and capabilities—but in this framing they cannot be said to “drive” migration. While they do not directly invoke aspirations and capabilities theory, in their study of climate related mobility owing to seaward impacts in the Ganges Delta, Adams and Kay (2019) speak of the “psychological propensity to move” and “mobility potential,” meaning that some are more predisposed to move, either because of aspirations or disaffection with place. We return to this theory in discussions on the way forward (section The Way Forward).

Livelihood Framework

The Livelihood Framework is closely tied to Sen's capabilities theory ( Sen, 1984 ), which relates to what people can do or be with their entitlements, including rights to land and natural resources. While not commonly employed as a migration theory, the livelihood framework developed by the UK Department for International Development ( Carney, 1998 ) has been applied to migration studies, including environmentally induced migration ( de Sherbinin et al., 2008 ; Tacoli, 2011 ; Hunter et al., 2015 ). Theorizing in this area links migration to livelihood strategies and the five livelihood assets—social, human, natural, physical, and financial capital. The livelihood approach is often associated with NELM, since a common assumption is that the capitals are household-based, but can also inform the capabilities part of the aspirations and capabilities theory. Environmental factors play a role primarily via natural capital, but can influence all types of capital.

Other Theories

This category includes theories that are not as prominent as the others, but which we included for completeness. For example, demographers have developed Life Course Analysis to focus on how migration is more prevalent at certain life stages ( McCollum et al., 2020 ). According to Wingens et al. (2011 , p. 1), “[T]he life course approach constitutes a promising conceptual starting point for overcoming the crucial micro-macro problem in social research by analyzing the dynamic interrelation of structure and agency.” Life course can be applied to climate mobility studies by looking at the propensity by age group and marital and family status of people to move given different climate-related stressors or disasters ( Entwisle et al., 2020 ). Other theories include Imaginaries ( Salazar, 2011 ), which focuses on people's perceptions, cultural norms, and expectations ( Hochleithner and Exner, 2018 ). Finally, some agent-based modelers (e.g., Kniveton et al., 2011) have adopted the Theory of Planned Behavior ( Ajzen, 1991 ), which holds that intentions to migrate can be predicted with high accuracy from attitudes toward migration, subjective norms surrounding migration that are socially constructed, and perceived behavioral control. We address the kinds of “other theories” employed in our sample of studies in the next section.

How Theory is Employed in the Empirical Literature

The focus of this paper is on the migration theories employed in qualitative and quantitative studies of climate-induced migration, including modeling work that projects future migration. We take 2010 as a starting point for our literature review since, by that time, the field of climate migration research had sufficiently matured, and after that date there began to be a rapid growth in published empirical studies on the subject ( Piguet, 2021 ; Šedová et al., 2021 ). We reviewed English-language peer reviewed journal articles (73) and book chapters (2) that fell into one or more of the following categories of empirical research:

1. Repurposed demographic and other data : These studies employ direct or indirect measures of migration from censuses or large-scale demographic surveys collected for other purposes, coupled with broad scale environmental/climate data, either for one time slice or across several time slices. Studies applying “big data” such as cell phone call detail records were included in this category. These studies range in scale from global to local. This category mostly maps to Piguet's (2021) Type 1 “spatial analysis,” but also includes some studies that may fall in Type 2 “multilevel analysis.”

2. Migration focused survey methods : These studies employ tailored surveys of individuals or households that focus on migration (e.g., past migration history, event history), and either connected to area data on climate, or on individual perceptions of climate variability. These generally focus on more local scales. This category mostly maps to Piguet's Type 3 “survey,” but also to the Type 2 “multilevel analysis.”

3. Qualitative field studies : These mostly local-scale studies employ anthropological techniques, focus group discussions, open interviews, life history, and participant observations related migration behavior, often coupled with data on perceptions of climate variability and change. This category maps to Piguet's Type 6 “qualitative.”

4. Modeling, projections and future scenarios studies : These studies deploy a range of approaches, including agent-based modeling (ABMs), system dynamics, statistical extrapolation (using type 1 data), population gravity modeling, and radiation modeling. These range in scales from global to local. This category is not included in Piguet's typology, though he does mention ABMs in his section addressing Types 2 and 3.

We used a purposive sampling approach that sought to capture a critical mass of studies under each category as well as a diverse representation across the multiple dimensions of our sample—i.e., category of study, discipline of authors, regions covered, temporal distribution, among others. Hence, our literature search did not rely on the common approach to systematic reviews (e.g., a standardized approach using Boolean search terms), but rather took an iterative approach, assessing our coverage after reviewing 50 articles, and adjusting the sample to cover a sufficient number in each category, with additional studies being identified using keyword searches on the CLIMIG database (University of Neufchatel). The goal was “theoretical saturation”—a point at which additional studies would not contribute substantially to our findings ( Saunders et al., 2018 ; Hennink and Kaiser, 2022 )—since the review is aimed less at painting a comprehensive picture across all climate-migration literature than acting as a springboard for discussion of how to better embed migration theory in climate mobility research. Supplementary Table 3 presents a full list of papers reviewed.

As a guide for representativity, we compared our sample to Piguet's (2021) typology, from which we derived our own. Piguet found that out of the 635 empirical studies in the University of Neufchatel's CLIMIG database, 37% were multilevel or survey studies (mostly our Category 2), 30% were qualitative (our Category 3), 15% were spatial analysis (mostly our Category 1), and the remaining 19% were historical analogs and hotspots, which we did not include. Recognizing that not all studies fit neatly into one category, we allowed for primary and secondary category coding. Studies were coded in such a way that both the category of study and the theory applied could have primary and secondary responses, because the same paper may apply different approaches and more than one theory. Combining both primary and secondary types, in our sample of 75 studies representing 108 primary and secondary categories, 33% were repurposed data, 30% were migration focused surveys, 21% were qualitative field surveys, and 16% were projections and future scenarios ( Figure 1 ). These percentages roughly correspond to those indicated by Piguet when accounting for differences in the categorization. Data on theories employed are presented in the next section. In terms of temporal distribution, 23, 37, and 40% of studies were published between 2010–2013, 2014–2017, and 2018–2021, respectively, generally reflecting the growth in the literature over the 12 year period. While we sought to capture a range of empirical study types, publication dates, regions, and disciplines, we acknowledge that the sample we used is neither fully representative of all climate mobility empirical literature, nor are our methods replicable.

Figure 1 . Study categories included in the sample.

In terms of regional representation, of our sample of 75 studies, 24 included Asia, 24 included Africa, 12 included Latin America, 4 included Oceania, 4 included North America, 9 were global in scope, and 1 included Europe. Again, some studies included more than one region. Finally, in terms of post-processing, we recoded disciplines into seven categories, preserving the most represented disciplines (e.g., geography, economics, sociology/demography, political science), but grouping others into three categories: computer science and modeling, natural and physical sciences, and other social sciences.

The range of empirical studies include studies focusing on rapid onset displacement, migration induced by slow or creeping onset events such as sea level rise and multi-year droughts, and studies focusing on a combination of climate and other environmental stressors. For each study we coded the climate factors examined, with some studies including multiple factors. Out of the 75 studies, 46 examined climate variability (mostly precipitation variability); 17 examined extremes such as cyclones, floods or extreme heat; 11 were coastal studies focused on sea level rise and associated impacts; and 7, 6, and 3 included consideration of longer term trends in temperature or precipitation, broader environmental changes, and glacial retreat, respectively.

Out of our sample of 75 studies, the highest portion of primary references were to New Economics of Labor Migration (NELM) (21%), other theories (19%), neoclassical (17%), and environmental migration frameworks (13%), with fewer than 10% each across the others. Table 1 shows the total and percentage of studies that referenced different theories (or no theory). When considering both primary and secondary theory references, NELM and other theories are most cited, at 24% of cases each, followed by environmental migration frameworks and neoclassical, at 21% each, and livelihoods and push-pull at just around 16% each. The predominance of NELM as a primary theory is likely attributable to its relevance to household risk management in the context of climate shocks.

Table 1 . Theories cited in the sample.

“Other” (non-migration) theories were widely cited. Breaking down this category, we find that theories cited include behavioral theory (four studies), which underlies the model of private proactive adaptation and protection motivation theory (PMT; Grothmann and Patt, 2005 ), life course theory ( Elder et al., 2003 ), social network theory, “mobilities theory” ( Sheller and Urry, 2006 ), theory of planned behavior ( Ajzen, 1991 ), socio-ecological systems theory ( Hummel et al., 2011 ), grounded theory 8 ( Charmaz, 2014 ), cultural ecology, political economy, and Reuveny's theory of three adaptations to environmental stress ( Reuveny, 2007 ). The adoption of behavioral theory, which differentiates between risk appraisal and subjective adaptation appraisal (evaluation of the ability to avoid being harmed), to migration research is a relatively recent development, only appearing in studies published after 2016.

Six studies cited no theory (8%) and 22 studies (29%) only made an implicit reference to the theory that guided their work—meaning that fully one-third of our sample engaged with theory to only a limited degree. In the latter case, the theoretical references emerge from the introductory material, data analysis, or findings, but there is no explicit discussion of theory or citations of theoretical works. For these studies, authors frequently stated that the main purpose of the research was to contribute to the empirical evidence for understanding climate's impact on migration. Thus, the data, in a sense, “speak for themselves,” which means that the authors generally have not thought about the framing of their work in a larger body of evidence or contributing to the advancement of theory.

A primary interest is how researchers from different disciplines apply theory to their studies, so we begin by examining the theories invoked by the discipline of lead authors. In terms of disciplines, 32% of our sample were papers led by geographers, followed by economists (27%), sociologists and demographers (15%), computer scientists and modelers (8%), natural and physical scientists (7%), other social scientists (7%), and political scientists (5%). Interdisciplinarity is important in climate migration research, and two-thirds of our sample had more than one author. Among secondary authors, the mix of disciplines was 27% geography, 26% economics, 22% all other social sciences, 14% Earth and natural sciences (including 7% climate science), 5.5% computer science and modeling, and 2.7% each public health and ecology.

Figure 2 shows the proportion of primary theories cited by the discipline of lead authors across the top four disciplines. Geographers tend to draw heavily on other theories, environmental migration frameworks such as the Foresight framework, NELM, and livelihood frameworks. Not surprisingly, over half of economists cite neoclassical migration theory followed by NELM, livelihood frameworks and other theories. A third of studies by sociologists and demographers cite NELM, followed by an equal split among other major theories. A higher proportion of sociologists cite theories of sustained migration than among other disciplines, and they are the only group that cites mobility transition theory. Among the remaining groups of disciplines (natural and physical scientists, political scientists, and other social scientists), NELM, other theories, and environmental migration frameworks are popular. Push-pull theory is the predominant theory cited by computer scientists and modelers. Livelihood frameworks are widely cited across all disciplines, yet NELM is the most widely applied primary theory, accounting for 16 of 75 studies. Roughly a quarter each of those studies citing NELM are by geographers and sociologists/demographers, followed by 19% by economists.

Figure 2 . Theories cited by discipline of lead authors.

Disciplines have specific patterns of engagement with theory. Sociologists and demographers often engage in theory related to life stages and other demographic processes (e.g., Entwisle et al., 2020 ), whereas geographers are more likely to adopt livelihood or political economy approaches. We address this more in the next section.

In terms of the theories cited by category of research ( Supplementary Table 2 ), the largest category in our sample is migration-focused surveys (Category 2), with 25 studies, 40% of which invoke NELM, with a smattering of other types. Twenty-seven percent of repurposed demographic data studies (Category 1) invoke neoclassical theory, followed by NELM (18%), perhaps reflecting the large proportion of economists who tend to analyze secondary data from censuses and surveys. Qualitative field studies (Category 3) cite in equal proportions environmental migration frameworks and other theories (22% each), while projections and future scenarios studies (Category 4) predominantly cite neoclassical theory (22%), followed by push-pull and other theory, at 14% each. These theoretical framings may be easier to code in quantitative models.

Finally, we explored the possibility that there might be temporal or regional patterns to the theories cited. Temporal trends were not noticeable in the relatively short period covered, except some more recent theories like aspirations and capabilities were not cited earlier in the period. In terms of regional breakdown, NELM, livelihood and environmental migration frameworks—many of which emphasize the effects of climate change on small-holder farmers and pastoralists—make up half the theories cited for African studies, and 44% of those in Asia. Similarly, NELM and environmental migration frameworks make up almost 50% of studies in Latin America.

The Way Forward

Empirical research is a key component of theory building, because it allows for theories to be examined, refuted, and refined based on real-life experiences. As part of this process of theory development, it is especially important to assess whether a theory can be considered “good” relative to alternative theories ( Popper, 1963 ) 9 . In this section, we examine some exemplary contributions from the corpus of climate migration research and various disciplines to migration (and mobilities) theory, discuss how theories address forced migration and involuntary immobility, and propose some paths forward.

As the review here shows, a critical issue for how theory is employed is that it focuses attention on certain things and, unless one is careful, not others. In other words, researchers approach their data expecting to see certain dynamics or relationships, which increases the likelihood of finding them. If the research question is something like, “what is the role of environment in migration,” there is a good chance that researchers simply will not recognize other processes beyond environmental conditions like cumulative causation, structural factors, or political economic factors that condition migration decision-making. Environmental migration and push-pull framings tend to privilege environmental factors ( De Haas, 2011 ), even when those frameworks recognize that environmental factors work through other more proximate determinants such as socioeconomic drivers. As Hunter (2005) notes, while contextual factors are often noted in theoretical perspectives on environmental migration, they are rarely emphasized.

As such, the climate migration literature often gives insufficient attention to the underlying culture and political economy of migrant sending areas ( Morrissey, 2012 ). Local laws and policies, markets rigged against smallholders, and political disenfranchisement all condition vulnerability, and climate factors may only be the final “nudge” that pushes people to leave their communities (e.g., Ribot et al., 2020 ). This may be why our analysis shows that “other theories” are the most invoked by researchers undertaking field studies, because many of these theories seek to understand complex socio-environmental systems and to explore behavioral aspects of mobility. Yet for studies relying on secondary data (Category 1 and sometimes Category 2), an understanding of local contexts is often missing, and they depend heavily on neoclassical and NELM theories. Decolonizing climate-migration research is only beginning to be addressed by some authors ( Gonzalez, 2020 ), but has yet to be addressed widely, especially in the migration as adaptation literature, where the benefits of migration for adaptation are often uncritically accepted ( Bettini and Gioli, 2015 ) with little recognition that those doing the adapting have been forced to do so owing to the historical emissions of affluent nations ( Samson et al., 2011 ).

Another issue is that it is conceivable that many people do not identify a theoretical framing, but in the review process they may be asked to consider how their findings relate to theory, which leads them to apply a theory ex post facto . Unless explicit attention is given to linking theory to research designs, or there is a robust discussion of how the work contributes to theory, it is often hard to discern the importance of theory to a given work. In light of that, we explore a few exemplary studies that stand out in terms of their treatment of theory.

Exemplary Studies

Based on more than two decades of research in Nang Rong district, Thailand, Entwisle et al. (2020) use an agent-based model to test theories related to life course transitions, evolving household economic strategies, and changes in social networks at and between places of origin and destination. They posit that this broader demographic/life course perspective is missing from much of the economic literature, with its focus on labor migration. They write, “By incorporating a life course perspective, including a focus on outmigration and return migration associated with the transition to adulthood, and embedding these in a systems approach, we identify a type of climate change impact that heretofore has not been considered: disruptions to established and expected streams of return migration” (p. 1,471). Their results underscore the importance of social networks for both out-migration and return migration.

Lalou and Delaunay (2017) , in their exploration of migration in rural Senegal, reject the neo-Malthusian framing of environmental migration as a mechanical and “naturalizing” explanation for migration, which characterizes migration as a forced displacement, and turn instead to NELM, the structuralist approach, social network theory and transnationalism theory, “which all suggest in their own way that environmental migration is not only a response to a strong stimulus from the natural environment but is also migration per se with complex causality and a decision process” (p. 270). They argue, as does Doevenspeck (2011) , that it therefore should not be analyzed as totally different in comparison with other forms of migration. They also draw on translocalism, stating though many studies focus on sending areas, the reality is that “migrants maintain links with their home village and participate actively in food security and sometimes in the development of their community's agricultural or non-farming activities” (p. 270). They see seasonal and temporary migration being a part of the adaptive strategy of households to risk, rather than as a failure to adapt.

Grace et al. (2018) use a livelihood diversification framework to investigate the relationship between rainfall variability and out-migration in two agriculture-dependent Malian villages where temporary out-migration is well-established. Their study design is based on livelihood and NELM theory, hypothesizing that in poor rainfall years their study communities would experience “either an increase in out-migration or changes in migration behaviors, as migrants and their families seek opportunities to diversify their income sources and reduce risk“ (p. 188). The fact that the evidence pointed to reductions in local temporary migration during years following poor rainfall led them to reconsider their hypotheses, positing that the same climate impacts may be experienced by other communities within the region, meaning fewer opportunities outside the village, or that liquidity constraints resulting from climate impacts reduce migration. The authors analyze their data by age and sex, giving an important demographic perspective to their work, and include a researcher from the country of focus on their team.

Barbieri et al. (2010) engage in an extensive review of theory in their study of climate factors influencing migration in Brazil's Northeast. They write, “disciplinary perspectives have constrained the development of more comprehensive conceptual and modeling approaches unveiling how environmental drivers of migration—particularly climate change—are embedded in other socioeconomic, cultural, political and institutional dimensions” (p. 347). They propose a model in their article that seeks to better marry economic theory with environmental drivers, by embedding climate impacts into the IMAGEM-B economic model, exploring links between climate change and economic dynamics (particularly income and employment levels), and how they affect population migration.

Disciplinary Approaches to Theory

Our relatively small sample of studies suggests that sociologists are the most likely to thoroughly embed their studies in theory. One of the first and most detailed explorations of theory in relation to environmental displacement and migration was by sociologist Lori Hunter in her 2005 paper “Migration and environmental hazards” ( Hunter, 2005 ). A decade later, Hunter et al. (2015 , p. 379) argued that “theory must effectively integrate the interactions between environmental factors and other migration determinants operating differentially across scales and across time,” including socioeconomic and sociopolitical conditions as well as household compositional characteristics. By the same token, they argue that “in the midst of contemporary climate change, environmental considerations should play a more central role in migration theory, particularly in relation to livelihoods and environmental conditions (both amenities and disamenities) in both urban and rural settings” (p. 387). Building on this, Hunter and Simon (2022) argue that it is important to account for environmental effects in models that explain migration, which otherwise risk misspecification of these effects to socioeconomic determinants. Sociologist/demographer Elizabeth Fussell, who has studied the climate displacement resulting from Hurricane Katrina in New Orleans, has also contributed significantly to theoretical discussions, pointing out how theory is linked to methods (e.g., how environmental factors are often included by economists in multivariate regression models used in studies of labor migration) and findings ( Fussell, 2012 ).

Geographers have also been at the forefront of theoretical discussions. Graeme Hugo, a population geographer, was a pioneer in the field, and among the first to theorize that environmental migration falls at the “forced end” of a voluntary-to-forced continuum ( Hugo, 1996 ). In a later paper in Global Environmental Change , Hugo (2011) includes one of the longest treatments of theory of recent reviews of climate-migration patterns and trends 10 . Hugo led a panel of the International Union for the Scientific Study of Population (IUSSP) on the demography of refugee and forced migration in which he and co-authors explore the importance of migration theories—both functional and structural—to informing the study of climate and other forms of forced migration ( Hugo et al., 2018 ). Political geographers Stephan Hochleithner and Andreas Exner conduct an extensive review of theory for a paper focusing on environmental migration in West Africa in the context of a project led by the Swedish International Centre for Local Democracy ( Hochleithner and Exner, 2018 ). Their consideration of how theory relates to processes in this region is one of the most complete explorations to date in the environmental migration literature.

Geographers fundamentally engage with mobility, often by reflecting on how people interact with place and each other as a natural aspect of human existence. In other words, everything they do consider how people exist within a specific place and how mobility and movement shape and are shaped by an individual's life (e.g., Gidwani and Sivaramakrishnan, 2003 ; Carr, 2005 ). This approach provides a much more advanced and nuanced conceptualization of mobility across space and time than those frequently adopted by economists or demographers, and is often grounded in theories that go beyond migration theory, including the new focus on mobilities—which embraces all forms of movement (e.g., voluntary and forced migration, displacement, daily movements, tourism) as well as immobility ( Sheller and Urry, 2006 ; Boas et al., 2019 ; Cundill et al., 2021 ). This helps to explain why among geographers, “other theories” represent the largest portion of theories invoked. For example, Quinn et al. (2018) focus on coastal climate mobility in an area near Marseille, France, deploying a social-ecological systems (SES) approach and place theory ( Chapin and Knapp, 2015 ; Masterson et al., 2017 ) to better understand how people register, experience, and manage SES change. In their view, an SES approach produces a dynamic understanding of sense of place, emphasizing that the way people relate to their local areas sits within wider social and ecological changes. For his part, Wrathall (2012 , p. 584) suggests “environmental migration can be viewed as a facet of social-ecological regime shift.” In other work, Wrathall et al. (2014) invoke political economic theory to understand how environmental stresses further reduce access to resources for the rural poor of coastal Honduras and highland Peru, reinforcing power structures in ways in which migration becomes the only option. These are but a few examples of the theoretical eclecticism of geographic thought on migration.

Theories of Forced Migration and Involuntary Immobility

We agree with Piguet (2018) that forced migration is an area requiring more theorization. Hugo (1996) recognized that mobility does not fit neatly in discrete categories but is on more of a spectrum from voluntary to forced, with environmental migration being conceived as more on the forced end. Yet even at this forced end of the spectrum, McLeman and Ploeger (2012) note that not everyone moves during a drought (or for that matter following a flood or cyclone), which opens a range of theoretical questions. Indeed, 45 years ago Nigerian demographer Aderanti Adepoju observed: “The preoccupation with the question of motivation (why people migrate?) tends to obscure the other side of the picture—and indeed a large part—which deals with the question of non-mobility, that is, why most people do not migrate from the rural environment” (in Findley and Doumbia, 2011 ). Climate migration researchers are only beginning to examine theories of immobility. As Zickgraf (2021 , p. 1) notes, “Theoretically, …our understandings of immobility in relation to environmental change are underdeveloped and oversimplified, and do not do justice to the diversity, dynamism, or unevenness of (im)mobilities.”

Given that not all people move in situations of duress, an adequate mobility theory needs to explain why. The lack of theorization has been ascribed in part to policy categories of “refugees” and “forced migrants” as opposed to “voluntary migrants” ( Bakewell, 2008 ; Erdal and Oeppen, 2018 ) rather than to actual differences in circumstances and motivations, which may be mixed ( Van Hear et al., 2009 ). Fussell (2012) highlights volition as one of the three dimensions of migration theory (in addition to time and space), and agrees that it is precisely this legal categorization that has discouraged refugee and migration researchers from joining efforts to advance a theory of involuntary migration. She writes, “Although environmentally induced migration may be framed as voluntary, insofar as migrants make decisions, the predisposing conditions of those decisions—in this case the insufficiency of natural-resource- based livelihoods—arguably determine the outcome” (p. 18). On the other hand, Bettini and Gioli (2015) critique early neo-Malthusian approaches as asserting that migration is a “reactive survival strategy to which a [household] is forced when confronting a dose of environmental stress in excess of its coping capacity.” This is migration as failure to adapt which tends to couch migration in negative terms and portray migrants as passive victims without agency.

Beyond the now sterile debate between “maximilists and minimalists” and migration as adaptation or failure to adapt ( McLeman and Smit, 2006 ; Morrissey, 2012 ), however, there is real room for exploring degrees of volition in the context of climate mobility, and incorporating these considerations into migration theory and research. Erdal and Oeppen (2018) argue that “volition in relation to migration decisions is closely tied to available acceptable alternatives and the agency to act on those options. Whether someone's migration is labeled as voluntary or not, however, depends on the labellers' perception of what constitutes ‘acceptable' alternatives” (p. 987 emphasis added). Anything short of death may, depending on one's perspective, be deemed an acceptable alternative. If, for example, remaining in extreme poverty or in an environmentally degraded/hazard prone region is considered by the outside observer as acceptable, then migration will by definition be labeled as more or less voluntary. From a migrant perspective, perceptions of acceptable alternatives are shaped by the migrant's beliefs and access to information ( Colburn, 2008 ).

Increasingly the field of climate mobility is addressing the question of involuntary immobility, which again raises questions about why some are able to move while others cannot move or are resistant to doing so in spite of steadily worsening conditions. Theory can illuminate these cases. Adams and Kay's (2019) exploration of inherent propensity to migrate and Quinn's (2018) discussion of place attachment represent important contributions to theoretical discussions of why people do not move in the face of apparent risks. More recent work seeks to embed climate-migration scholarship in risk frameworks developed under the Intergovernmental Panel on Climate Change (IPCC) ( McLeman et al., 2021 ). This framing suggests that there is a predisposition for people to want to remain in place rather than migrate, because migration implies disruptions to households and communities, and that as risk levels increase or in situ adaptation is unsuccessful, thresholds are passed which result in the act of migration.

Aspirations and Capabilities Theory as a Recent Advance

Perhaps because of its relative recency, aspirations and capabilities theory was only invoked as a primary or secondary theory by five of the studies in our sample ( Table 1 ). The theory emerged in the early 2000s ( Carling, 2002 ; De Haas, 2010 ) and was further improved in the subsequent decade ( Carling and Schewel, 2018 ; De Haas, 2021 ). We expect that more empirical studies of climate mobility will make use of the aspirations and capabilities framework in the coming decade. The framework has the potential for advancing our understanding of the complex links between climate impacts and human mobility, and for addressing the range of potential mobility scenarios from voluntary to forced, and from mobile to immobile ( Table 2 ). It is able to explain, for example, why migration may decline in the aftermath of climatic events or when slow-onset processes cause gradually declining conditions for gaining a livelihood. In such circumstances, the aspirations to move increase, yet the ability to move, especially over longer distances, declines. Push-pull theory, neoclassical migration theory, NELM and other theories discussed in section Brief Review of Migration Theory are less able to capture the complex realities of a world in which different types of climatic stressors interact with different types of human mobility among heterogeneous populations with unequal access to resources needed to move or adapt locally ( Cundill et al., 2021 ). Using the aspirations and capabilities framework to guide field research design in diverse empirical settings across continents, climatic zones, socio-ecological systems and rural-urban divide, has the potential to yield new insights into climate mobilities.

Table 2 . Aspirations–capabilities-derived individual mobility types.

Peering Into the Future

Future modeling of climate-induced migration has heavily depended on neo-classical and push-pull theories (50 percent of the total sample). De Haas (2011) writes “While scenarios approaches focus on future constellations of contextual factors, it is important to also ground the assessment of the effects of contextual change on migration on state-of-the-art theories on migration determinants. This is important to emphasize, because much migration analysis in policy and, sometimes, research is still based on push–pull or gravity models, which can lead to misleading analyses of economic and environmental stress leading to mass migration” (p. S60). De Haas argues for a greater appreciation of structural and demographic factors that underlie major migration systems such as those between Africa and Europe and Central America/Mexico and the United States, which ultimately have greater predictive power than environmental influences. Modeling work would do well to consider a broader range of theoretical frameworks, which by extension likely implies greater complexity that better captures multiple causal paths and decision-making contexts.

We argue in this article that it is important for researchers to explicitly frame their work in theory, even when the research goal is simply to “fill knowledge gaps” or “contribute to the empirical evidence base” on climate mobility. The reality is that even in simply filling gaps, researchers carry models of how the world works in their minds, and those mental models guide their work. So it is far better to make those conceptual models explicit than to hide them under the guise of “letting the data speak for themselves.” Our results show that the application and testing of the rich body of migration theory by researchers in the domain of environmental and climate migration tends to be spotty at best. In fact, most researchers focus on theories such as NELM ( Stark and Bloom, 1985 ), with its emphasis on rural household-level decision making and migration as a risk reduction strategy, or the most recent conceptual models such as the Foresight framework ( Black et al., 2011 ; Foresight, 2011 ). While there is nothing inherently wrong with these theories, their frequent implementation may suggest that few alternative theories were considered by the authors, and hence tested. Furthermore, theories focusing on individual-level decision making (e.g., Carling and Schewel, 2018 ; De Haas, 2021 ) are often emphasized over structural theories that stress macroeconomic and demographic factors as fundamental explanatory factors underlying migration, particularly from lower income countries to higher income countries. Yet these structural approaches are often the most important for international migration studies ( Massey et al., 1993 ; De Haas, 2010 ; King, 2012 ; Clemens, 2021 ), and have extensive empirical evidence to validate them ( De Haas, 2011 ; Hochleithner and Exner, 2018 ). Finally, as we have addressed in the last section, there is little attention to theories of forced migration ( Erdal and Oeppen, 2018 ) or immobility ( Schewel, 2020 ; Zickgraf, 2021 ), both of which are critical to understanding climate mobility.

Importantly, theory can also inform (or misinform) policy. Theories contribute to development orthodoxies [e.g., modernization ( Rostow, 1959 ) and demographic transition ( Caldwell, 2007 ; Handwerker, 2019 )], and undergird the frequent neo-Malthusian framing of climate, conflict and the “threat” of mass migration ( Verhoeven, 2011 ) found so often in the media and development discourse ( De Haas, 2020 ; Durand-Delacre et al., 2021 ). This may lead to simplistic policy responses. The specter of mass migration owing to climate impacts has, in its best guise, been raised as a warning of the likely consequences of continued high emissions (e.g., Rigaud et al., 2018 ). At its worst, reference to “climate refugees” has fueled nationalistic and xenophobic responses, even when the intent is otherwise ( Durand-Delacre et al., 2021 ). In essence these are political messages. We have an obligation to ground politics and policy on the best theories and empirical research, which address different causal explanations and are based on a transdisciplinary perspective 11 .

In closing, beyond the ways in which this field employs theory, the emerging empirical research on climate mobility presents a wonderful opportunity for theory building. Rigorous interdisciplinary research in varied cultural and economic contexts—such as the studies being conducted by climate mobility researchers—is actually key to advancing theoretical approaches. Yet researchers have to show how their empirical work engages with theory, rather than simply referring briefly to the theoretical framing employed by their study before moving on to methods and results. Empirical research is a key component of theory building because it allows for theories to be examined, refuted, and refined based on real-life experiences ( Popper, 1963 ). Thus, we advocate for a two-pronged approach: build on existing theory on the one hand, and utilize approaches such as grounded theory ( Charmaz, 2014 ), in which theory is developed inductively through the analysis of empirical evidence, on the other. This will help to root climate mobility work in the broader corpus of migration studies and serve to enrich the theoretical bases for future work.

Data Availability Statement

The original contributions presented in the study are included in the article/ Supplementary Material , further inquiries can be directed to the corresponding author/s.

Author Contributions

AS conceived of the study and led the development of the literature survey (instrument, coding, etc.), coded studies, reviewed the literature on theory, and led the write up of results. KGr contributed substantially to the introduction, way forward, and conclusion sections. KGr, SM, KGe, MP, and AB contributed to the development of the instrument used to code theoretical approaches employed by the sample studies, conducted coding of studies, analyzed survey results, and contributed ideas and text to the manuscript. All authors contributed to the article and approved the submitted version.

AS, SM, MP, and AB would like to acknowledge funding from the NSF Global Convergence Research (GCR) project Collaborative Research: Disentangling Environmental Change and Social Factors as Drivers of Migration (NSF OIA Award 1934978; 1934955), and KGr would like to acknowledge funding from the NSF INFEWS research project Understanding multi-scale resilience options for vulnerable regions (NSF Award 1639214). MP acknowledges support from the Army Research Office/Army Research Laboratory under the Multidisciplinary University Research Initiative (Grant no. W911NF1810267).

Author Disclaimer

The views and conclusions contained in this manuscript are those of MP and his co-authors and should not be interpreted as representing the official policies either expressed or implied of the Army Research Office or the US Government.

Conflict of Interest

The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.

Publisher's Note

All claims expressed in this article are solely those of the authors and do not necessarily represent those of their affiliated organizations, or those of the publisher, the editors and the reviewers. Any product that may be evaluated in this article, or claim that may be made by its manufacturer, is not guaranteed or endorsed by the publisher.

Acknowledgments

The authors acknowledge intellectual contributions to transdisciplinary discussions and reading groups on climate mobility from colleagues on the NSF Global Convergence Research (GCR) project, including Richard Seager (PI), Wolfram Schlenker, and Fabien Cottier, as well as participants in the workshop, Workshop on Disentangling the Drivers of Migration in West Africa at Columbia University in February 2020. They also appreciate assistance with graphics development from Kaitlyn Bretz of the Columbia Climate & Society program.

Supplementary Material

The Supplementary Material for this article can be found online at: https://www.frontiersin.org/articles/10.3389/fclim.2022.882343/full#supplementary-material

1. ^ Theory has been defined as an “ordered set of assertions about a generic behavior or structure assumed to hold throughout a significantly broad range of specific instances” ( Sutherland, 1975 , p. 9), and has four components: “conceptual definitions, domain limitations, relationship-building, and predictions” ( Wacker, 1998 , p. 361). The special case of migration theory addresses fundamental questions such as who migrates; why do they migrate; what types of mobility do they employ; under what circumstances do they employ them; why do they choose certain destinations over others; and what are the conditions that shape return migrations? (for similar questions see Massey et al., 1993 ; Bakewell, 2010 ). When social scientists employ theory, they do so to help provide a systematic explanation for observations ( Babbie, 1989 ), and to organize disparate findings into a coherent picture in an effort to explain social phenomena and human behavior.

2. ^ A recent review by Hunter and Simon (2022) provides more examples of how environmental factors can and have been incorporated in five theoretical framings: neoclassical migration theory, migration systems, the push-pull model, new economics of labor migration, and political economic approaches.

3. ^ For example, the Foresight report ( Foresight, 2011 ) authors explicitly cite push-pull theory in their development of the widely cited diagram describing the ways in which environmental factors influence migration decision making. The Foresight framework explains linkages and pathways, but does not have explanatory power. In other words, it explicates how environmental factors largely work through other proximate factors (economic, demographic, etc.), but it cannot be used to predict how an environmental stressor will result in migration. Thus, according to our earlier definition it may fall short of being a “full” theory. Indeed, De Haas (2011) criticizes push-pull theory itself for being inadequate from an explanatory point of view.

4. ^ Because this has rarely been found to be the case, De Haas (2021) argues that theories focusing on the utility maximizing behavior of individual migrants or migrant-sending households fail to explain many of the patterns of migration that exist in the world.

5. ^ This is a simplification, of course. As Martin-Shields et al. (2017) point out, the Migration Hump “cannot be explained solely by rising incomes and increased education. It is also driven by other factors, including demographic transition, changes in economic structures, emulation effects in migration processes, rising inequality, credit restrictions and the lowering of migration barriers.” In addition, lack of good governance and limited prospects for a better life were often cited in UNDP's (2019) Scaling Fences report as motivations for migration among African migrants interviewed in Europe.

6. ^ According to Morawska (2007 , p. 12), “Structures [are] patterns of social (including economic and political) relations and cultural formations (re)constituted through everyday practice of social actors… [They] are plural in character (different-purpose organizations, strong and weak informal networks, [sub]cultures), scope (global, regional/national, local), dynamics (more or less stable), and durability (longer- to short-duration).”

7. ^ An ecological fallacy is when inferences about individual-level decision making are deduced from inferences about the group to which the individual belongs.

8. ^ This approach may be considered to fall in the “no theory” category by some, since it represents a way of conducting research that builds new theory based on the evidence collected in the field. The principle is to do research on a certain topic without the goal of testing any specific theory, but rather with the goal of building theory, or at least making generalizations, based on the observations and data. Grounded theory involves the application of inductive reasoning. It was applied by McLeman and Ploeger (2012) in their study of soil quality and its role as a mediating variable in drought migration from Saskatchewan in the 1930s.

9. ^ While there is no consensus on what a “good” theory is, most agree that a “good” theory should possesses certain virtues including “uniqueness, parsimony, conservation, generalizability, fecundity, internal consistency, empirical riskiness, and abstraction” ( Wacker, 1998 , p. 361).

10. ^ Compare Hugo's three-and-a-half page (27 paragraph) treatment of theories addressing demographic change, climate change and migration, for example, Kaczan and Orgill-Meyer's (2020) comparatively slender two paragraph treatment of theory in their review for Climatic Change .

11. ^ In this regard, it is important that theory and research not be based on predefined policy categories of migrants or driven solely by policy imperatives. As Bakewell (2008) notes, building on Turton (2003) , “the role of academic research should be to reflect critically on the taken-for-granted assumptions of policy makers rather than simply confirming or legitimizing them: to make them visible and open to inspection” (p. 437–438). Erdal and Oeppen (2018) call on “scholars to challenge the status quo more, not only by deconstructing government labeling, but also by further unpacking the assumed dichotomy between forced and voluntary migration, thereby examining voluntariness” (p. 994).

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Keywords: migration theory, climate migration, climate mobility, migration research, climate adaptation, human mobility, climate change, aspirations and capabilities

Citation: de Sherbinin A, Grace K, McDermid S, van der Geest K, Puma MJ and Bell A (2022) Migration Theory in Climate Mobility Research. Front. Clim. 4:882343. doi: 10.3389/fclim.2022.882343

Received: 23 February 2022; Accepted: 14 April 2022; Published: 10 May 2022.

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Copyright © 2022 de Sherbinin, Grace, McDermid, van der Geest, Puma and Bell. This is an open-access article distributed under the terms of the Creative Commons Attribution License (CC BY) . The use, distribution or reproduction in other forums is permitted, provided the original author(s) and the copyright owner(s) are credited and that the original publication in this journal is cited, in accordance with accepted academic practice. No use, distribution or reproduction is permitted which does not comply with these terms.

*Correspondence: Alex de Sherbinin, adesherbinin@ciesin.columbia.edu

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How Do Environmental Factors Influence Migration?

By roman hoffmann (wittgenstein centre for demography and global human capital).

Source: RoschetzkyIstockPhoto

The impact of climate change on migration has gained both academic and public interest in recent years. Despite an increasing number of empirical studies, there is no scientific consensus as to what extent and under which conditions environmental factors influence migration. To fill this gap, I worked with my colleagues Anna Dimitrova, Raya Muttarak, Jesus Crespo Cuaresma and Jonas Peisker from the Wittgenstein Centre for Demography and Global Human Capital (IIASA, Austrian Academy of Sciences, University of Vienna) to conduct a meta-analysis on the relationship between environmental change and migration. This article is now available in Nature Climate Change . Based on 30 original studies, we show how environmental factors influence migration in different contexts.

In our meta-analysis we find robust evidence that environmental factors explain migration patterns . However, the size of the relationship strongly depends on the particular economic and sociopolitical contexts, as well as the environmental factors under consideration. The strongest environmental impacts on migration are found in studies with a large share of non-OECD countries, particularly from Latin America and the Caribbean and Sub-Saharan Africa (Sahel region and East Africa). Furthermore, we find stronger migration responses in studies focusing on middle-income and agriculturally dependent countries, and weaker responses in studies concentrating on low and high-income countries. This suggests an inverted U-shaped relationship between socio-economic development and migration.

Map Predicted Enviornmental Migration Binary Outcome

The commonly found narrative of climate refugees pushing towards Europe or the U.S. is in many ways too simplistic. Our findings suggest that environmental impacts result mainly in internal migration or migration to low- and middle-income countries, rather than cross-border migration to high-income countries. Taken together, the results of our meta-analysis mirror the findings in the empirical literature, which reports that environmental migration is often short-distance, regional, and temporary. Affected populations typically migrate to places within their own region and eventually return to their homes within a relatively short period of time.

Different types of hazards have differential impacts on livelihoods and can both amplify or suppress migration. Comparing a range of environmental drivers, our findings suggest that increasing temperatures and temperature extremes, followed by rapid-onset events (e.g. hurricanes or tsunamis) and precipitation anomalies (e.g. changes in rainfall variability and patterns) have the strongest impacts on migration. Importantly, the different environmental drivers are not independent, but closely connected and can reinforce each other in influencing migration.

Environmental conditions alone are rarely the only migration driver, but one of many that influence migration. They shape various macro, meso, and micro factors influencing the decision of households to move. Our meta-analysis provides additional support for the role income changes and conflict play in explaining environmental migration. Environmental change can disrupt livelihoods and lead to the onset and spread of conflicts in certain contexts, especially where governance is weak.

Given the expected rise of global average temperatures due to climate change, our results have important implications for global policy discussions, highlighting the role of contextual factors in influencing environmental migration . Environmental factors can be an important migration driver, but there is no automatism at play. While in some contexts, changing conditions lead to increased migration, they have no effect or constrain migration in other contexts. Policy interventions thus have to be tailored to the actual situations on the ground to effectively support affected populations.

A particular focus should be placed on those groups most vulnerable to environmental change. This includes migrants as well as people who decided to (voluntarily or involuntarily) stay in an affected region. While migration can be an effective adaptation strategy for households, it can be forced and come with non-negligible consequences for the migrants, their household members and their communities. People fleeing for their lives require special protection and support; and it is the responsibility of every country and the international community to ensure that this protection is granted.

This work would not have been possible without the generosity and contributions of the authors of the papers included in our meta-analysis who kindly shared their data and codes with us. We are very thankful for their support.

Additional Information

Authors of original article.

Hoffmann, R., Dimitrova, A., Muttarak, R., Crespo Cuaresma, J. & Peisker, J. (2020). A meta-analysis of country-level studies on environmental change and migration. Nature Climate Change. https://doi.org/10.1038/s41558-020-0898-6

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Environmental Migration

Environmental change and disasters have always been major drivers of migration. However, climate change predictions for the 21st century indicate that even more people are expected to be on the move as extreme weather-related events, such as floods, droughts and storms become more frequent and intense ( IPCC , 2014), and changes in precipitation and temperature patterns impact livelihoods and human security.

The 2018 Global Compact for Safe, Orderly and Regular Migration (GCM), the first-ever negotiated global framework on migration, recognizes that migration in the context of disasters, climate change, and environmental degradation is a reality, and makes commitments to support both migrants and States.

No legal definition for persons on the move due to environmental drivers exists to date and neither an internationally accepted one. However, many actors work on these links, including IOM, and have developed conceptual frameworks to work with. IOM put forward in 2007 a broad working definition for Environmental Migration , which seeks to capture the complexity of the issues at stake.

“Environmental migrants are persons or groups of persons who, predominantly for reasons of sudden or progressive change in the environment that adversely affects their lives or living conditions, are obliged to leave their habitual homes, or choose to do so, either temporarily or permanently, and who move either within their country or abroad” ( IOM , 2007:33).

This definition is deliberately broad and flexible in order to account for the diverse range of population movements due to all types of environmental drivers. This definition shows that environmental migration can take many complex forms: forced and voluntary, temporary and permanent, internal and international, individual and collective, of proximity and of long distance. The nature, duration and scale of environmental migration also depends on whether it takes place in the context of slow-onset events and processes (sea level rise, increasing temperatures, land degradation, etc) or sudden-onset events and processes (floods, cyclones, storms, etc.) that are exacerbated by the adverse effects of climate change and environmental degradation. It also depends to what extent it interacts with other socio-economic, cultural and political factors that influence the decision or necessity to move. Because of this complexity and multicausality, environmental migration should not be understood as a wholly negative or positive outcome – migration can amplify existing vulnerabilities, but it can also allow people to build resilience.

In the absence of a legal definition or an internationally accepted one, several other proposals were made on categorizing the movements of people due to environmental drivers. They usually propose a narrower definition by either focusing on one type of movement (for instance displacement) or one type of environmental driver (for instance climate change impacts).

Climate migration refers to “the movement of a person or groups of persons who, predominantly for reasons of sudden or progressive change in the environment due to climate change, are obliged to leave their habitual place of residence, or choose to do so, either temporarily or permanently, within a State or across an international border” ( IOM , 2019). Climate migration is thus a subcategory of environmental migration; it defines a singular type of environmental migration, where the change in the environment is due to climate change. While, this is an IOM working definition with an analytic and advocacy purpose which does not have any specific legal value, the term is used in the legally-binding Cancun Agreements on climate change adaptation , adopted by States Parties to the UN Framework Convention on Climate Change (UNFCCC) at the 2010 Conference. The Cancun Agreements identify three forms of “climate change induced” movement: displacement, migration, and planned relocation. The term has also been employed by the World Bank in projecting future movements due to the adverse impacts of climate change.

Planned relocation “in the context of disasters or environmental degradation, including when due to the effects of climate change, [refers to] a planned process in which persons or groups of persons move or are assisted to move away from their homes or place of temporary residence, are settled in a new location, and provided with the conditions for rebuilding their lives. The term is generally used to identify relocations that are carried out within national borders under the authority of the State and denotes a long process that lasts until “relocated persons are incorporated into all aspects of life in the new setting and no longer have needs or vulnerabilities stemming from the Planned Relocation”” ( IOM , 2019; Georgetown University, UNHCR, and IOM, 2017 ; UNHCR, the Brookings Institution and Georgetown, 2015).

Disaster displacement is a term that “refers to situations where people are forced to leave their homes or places of habitual residence as a result of a disaster or in order to avoid the impact of an immediate and foreseeable natural hazard. Such displacement results from the fact that affected persons are (i) exposed to (ii) a natural hazard in a situation where (iii) they are too vulnerable and lack the resilience to withstand the impacts of that hazard” (Nansen Initiative, 2015). This term is mostly used to identify forced movements of people triggered by sudden-onset events in the environment. The concept of “cross-border disaster-displacement” is also sometimes associated with this term, particularly identifying the destination of population movements, to another country. “Disaster displacement” is used and promoted in the work of the Platform on Disaster Displacement as an umbrella term, while humanitarian agencies like IOM and UNHCR employ it with the narrow scope of forced sudden movements. The term is also used by the Internal Displacement Monitoring Centre (IDMC) in presenting annual estimates on new internal displacements in the context of disasters.

Human mobility is “a generic term covering all the different forms of movements of persons. The term human mobility reflects a wider range of movements of persons than the term “migration”. The term is usually understood as also encompassing tourists that are generally considered as not engaging in migration” ( IOM , 2019). In the context of environmental drivers, human mobility is being used within the work of UNFCCC, where the Executive Committee of the Warsaw International Mechanism on Loss and Damage associated with climate change has a strategic workstream (d) dedicated to human mobility, and where the several international organizations have created the “Advisory Group on Climate Change and Human Mobility.” In this context, human mobility is understood as encompassing the three forms of “climate change induced” movement from the Cancun Agreement , namely, displacement, migration, and planned relocation. The term is increasingly used in multi-stakeholder engagements, as actors working on the different types of movements of people can easily converge towards it.

Climate refugee or environmental refugee are terms frequently used on purpose in the media and by activists to draw attention on the situation and needs of those uprooted because of disasters, climate change and environmental degradation. While their situations and needs can be similar to those of refugees, such as crossing a border after a disaster and needing protection and assistance, people moving for environmental reasons, do not fall squarely within any one particular category provided by the existing international legal framework. Terms such as "climate change refugee" or "environmental refugee" have thus no legal basis in international refugee law. There is also a growing consensus among concerned agencies, including IOM and UNHCR , that their use is to be avoided. These terms are misleading and fail to recognize a number of key aspects that define population movements in the context of climate change and environmental degradation, including that environmental migration is mainly internal and not necessarily forced, and the use of such terms could potentially undermine the international legal regime for the protection of refugees. In addition, all persons moving in the context of environmental drivers are protected by international human rights law. Persons displaced within their country due to disasters caused by natural or human made hazards are also covered by provisions laid out in the Guiding Principles on Internal Displacement. This coverage is contingent on the extent to which a country has adopted the Guiding Principles.

While this terminology analysis focuses on movement, it is important to note that the concept of “vulnerability” needs to be put at the centre of current and future responses to environmental migration. The most vulnerable may be those who are unable to or do not move (trapped populations).

Trapped populations are those “who do not migrate, yet are situated in areas under threat, […] at risk of becoming ‘trapped’ or having to stay behind, where they will be more vulnerable to environmental shocks and impoverishment. The notion of trapped populations applies in particular to poorer households who may not have the resources to move and whose livelihoods are affected” ( IOM , 2019). In the context of climate change, some populations might not be able to move due lack of resources, disability or social reasons (e.g. gender issues), and other might choose not to move due cultural reasons, such as the ancestral links people have with their land.

International Organization for Migration 2019 Glossary on Migration, International Migration Law No. 34 2014 Glossary on Migration, Environment and Climate Change: Evidence for Policy 2014 IOM Outlook on Migration, Environment and Climate Change 2007 Migration and the Environment. Discussion Note: MC/INF/288 , prepared for the Ninety-fourth Session of the IOM Council, 27–30 November 2007, Geneva.

Intergovernmental Panel on Climate Change (IPCC) 2018 Glossary In: Global Warming of 1.5°C. An IPCC Special Report on the impacts of global warming of 1.5°C

United Nations Framework Convention on Climate Change (UNFCCC) 2020 Glossary of Climate Change Acronyms and Terms

United Nations Office for Disaster Risk Reduction (UNDRR) 2020 Terminology on Disaster Risk Reduction

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Global migration: causes and consequences.

Benjamin Helms Benjamin Helms Department of Politics, University of Virginia
, and David Leblang David Leblang Department of Politics, Frank Batten School of Leadership and Public Policy, University of Virginia
https://doi.org/10.1093/acrefore/9780190228637.013.631
Published online: 25 February 2019

International migration is a multifaceted process with distinct stages and decision points. An initial decision to leave one’s country of birth may be made by the individual or the family unit, and this decision may reflect a desire to reconnect with friends and family who have already moved abroad, a need to diversify the family’s access to financial capital, a demand to increase wages, or a belief that conditions abroad will provide social and/or political benefits not available in the homeland. Once the individual has decided to move abroad, the next decision is the choice of destination. Standard explanations of destination choice have focused on the physical costs associated with moving—moving shorter distances is often less expensive than moving to a destination farther away; these explanations have recently been modified to include other social, political, familial, and cultural dimensions as part of the transaction cost associated with migrating. Arrival in a host country does not mean that an émigré’s relationship with their homeland is over. Migrant networks are an engine of global economic integration—expatriates help expand trade and investment flows, they transmit skills and knowledge back to their homelands, and they remit financial and human capital. Aware of the value of their external populations, home countries have developed a range of policies that enable them to “harness” their diasporas.

immigration
international political economy
factor flows
gravity models

Introduction

The steady growth of international labor migration is an important, yet underappreciated, aspect of globalization. 1 In 1970 , just 78 million people, or about 2.1% of the global population, lived outside their country of birth. By 1990 , that number had nearly doubled to more than 150 million people, or about 2.8% of the global population (United Nations Population Division, 2012 ). Despite the growth of populist political parties and restrictionist movements in key destination countries, the growth in global migration shows no signs of slowing down, with nearly 250 million people living outside their country of birth as of 2015 . While 34% of all global migrants live in industrialized countries (with the United States and Germany leading the way), 38% of all global migration occurs between developing countries (World Bank, 2016 ).

Identifying the causes and consequences of international labor migration is essential to our broader understanding of globalization. Scholars across diverse academic fields, including economics, political science, sociology, law, and demography, have attempted to explain why individuals voluntarily leave their homelands. The dominant thread in the labor migration literature is influenced by microeconomics, which posits that individuals contemplating migration are rational, utility-maximizing actors who carefully weigh the potential costs and benefits of leaving their country of origin (e.g., Borjas, 1989 ; Portes & Böröcz, 1989 ; Grogger & Hanson, 2011 ). The act of migration, from this perspective, is typically conceptualized as an investment from which a migrant expects to receive some benefit, whether it be in the form of increased income, political freedom, or enhanced social ties (Schultz, 1961 ; Sjaastad, 1962 ; Collier & Hoeffler, 2014 ).

In this article we go beyond the treatment of migration as a single decision and conceive of it as a multifaceted process with distinct stages and decision points. We identify factors that are relevant at different stages in the migration process and highlight how and when certain factors interact with others during the migration process. Economic factors such as the wage differential between origin and destination countries, for example, may be the driving factor behind someone’s initial decision to migrate (Borjas, 1989 ). But when choosing a specific destination, economic factors may be conditioned by political or social conditions in that destination (Fitzgerald, Leblang, & Teets, 2014 ). Each stage or decision point has distinguishing features that are important in determining how (potential) migrants respond to the driving forces identified by scholars.

This is certainly not a theoretical innovation; migration has long been conceived of as a multi-step process, and scholars often identify the stage or decision point to which their argument best applies. However, most interdisciplinary syntheses of the literature on international labor migration do not provide a systematic treatment of this defining feature, instead organizing theoretical and empirical contributions by field of study, unit or level of analysis, or theoretical tradition (e.g., Portes & Böröcz, 1989 ; Massey et al., 1993 ; European Asylum Support Office, 2016 ). Such approaches are undoubtedly valuable in their own right. Our decision to organize this discussion by stage allows us to understand this as a process, rather than as a set of discrete events. As a result, we conceptualize international labor migration as three stages or decision points: (a) the decision to migrate or to remain at home, (b) the choice of destination, and (c) the manner by which expatriates re-engage—or choose not to re-engage—with their country of origin once abroad. We also use these decision points to highlight a number of potential new directions for future research in this still-evolving field.

Figure 1. Global migration intentions by educational attainment, 2008–2017.

Should I Stay or Should I Go, Now?

The massive growth in international labor migration in the age of globalization is remarkable, but the fact remains that over 95% of the world’s population never leave their country of origin (United Nations Population Division, 2012 ). Figure 1 shows the percentage of people who expressed an intention to move abroad between 2008 and 2017 by educational attainment, according to data from the Gallup World Poll. Over this time period, it appears that those who were highly educated expressed intent to migrate in greater numbers than those who had less than a college education, although these two groups have converged in recent years. What is most striking, however, is that a vast majority of people, regardless of educational attainment, expressed no desire to move abroad. Even though absolute flows of migrants have grown at a near-exponential rate, relative to their non-migrating counterparts, they remain a small minority. What factors are important in determining who decides to migrate and who decides to remain at home? 2

From Neoclassical Economics to the Mobility Transition

Neoclassical economic models posit that the primary driving factor behind migration is the expected difference in wages (discounted future income streams) between origin and destination countries (Sjaastad, 1962 ; Borjas, 1989 ; Clark, Hatton, & Williamson, 2007 ). All else equal, when the wage gap, minus the costs associated with moving between origin and destination, is high, these models predict large flows of labor migrants. In equilibrium, as more individuals move from origin to destination countries, the wage differential narrows, which in turn leads to zero net migration (Lewis, 1954 ; Harris & Todaro, 1970 ). Traditional models predict a negative monotonic relationship between the wage gap and the number of migrants (e.g., Sjaastad, 1962 ). However, the predictions of neoclassical models are not well supported by the empirical record. Empirical evidence shows that, at least in a cross-section, the relationship between economic development and migration is more akin to an inverted U. For countries with low levels of per capita income, we observe little migration due to a liquidity constraint: at this end of the income distribution, individuals do not have sufficient resources to cover even minor costs associated with moving abroad. Increasing income helps to decrease this constraint, and consequently we observe increased levels of emigration as incomes rise (de Haas, 2007 ). This effect, however, is not monotonic: as countries reach middle-income status, declining wage differentials lead to flattening rates of emigration, and then decreasing rates as countries enter later stages of economic development. 3

Some research explains this curvilinear relationship by focusing on the interaction between emigration incentives and constraints : for example, increased income initially makes migration more affordable (reduces constraints), but also simultaneously reduces the relative economic benefits of migrating as the wage differential narrows (as potential migrants now have the financial capacity to enhance local amenities) (Dao, Docquier, Parsons, & Peri, 2016 ). The theoretical underpinnings of this interaction, however, are not without controversy. Clemens identifies several classes of theory that attempt to explain this curvilinear relationship—a relationship that has been referred to in the literature as the mobility transition (Clemens, 2014 ). These theories include: demographic changes resulting from development that also favor emigration up to a point (Easterlin, 1961 ; Tomaske, 1971 ), the loosening of credit restraints on would-be migrants (Vanderkamp, 1971 ; Hatton & Williamson, 1994 ), a breakdown of information barriers via the building of transnational social networks (Epstein, 2008 ), structural economic changes in the development process that result in worker dislocation (Zelinsky, 1971 ; Massey, 1988 ), the dynamics of economic inequality and relative deprivation (Stark, 1984 ; Stark & Yitzhaki, 1988 ; Stark & Taylor, 1991 ), and changing immigration policies in destination countries toward increasingly wealthy countries (Clemens, 2014 ). While each of these play some role in the mobility transition curve, Dao et al. ( 2016 ) run an empirical horse race between numerous explanations and find that changing skill composition resulting from economic development is the most substantively important driver. Economic development is correlated with an increase in a country’s level of education; an increase in the level of education, in turn, is correlated with increased emigration. However, traditional explanations involving microeconomic drivers such as income, credit constraints, and economic inequality remain important factors (Dao et al., 2016 ). The diversity of explanations offered for the mobility transition curve indicates that while most research agrees the inverted-U relationship is an accurate empirical portrayal of the relationship between development and migration, little theoretical agreement exists on what drives this relationship. Complicating this disagreement is the difficulty of empirically disentangling highly correlated factors such as income, skill composition, and demographic trends in order to identify robust causal relationships.

Political Conditions at the Origin

While there is a scholarly consensus around the mobility transition and the role of economic conditions, emerging research suggests that the political environment in the origin country may also be salient. We do not refer here to forced migration, such as in the case of those who leave because they are fleeing political persecution or violent conflict. Rather, we focus on political conditions in the homeland that influence a potential migrant’s decision to emigrate voluntarily. Interpretations of how, and the extent to which, political conditions in origin countries (independent of economic conditions) influence the decision to migrate have been heavily influenced by Hirschman’s “Exit, Voice, and Loyalty” framework (Hirschman, 1970 , 1978 ). Hirschman argues that the opportunity to exit—to exit a firm, an organization, or a country—places pressure on the local authorities; voting with one’s feet forces organizations to reassess their operations.

When applied to the politics of emigration, Hirschman’s framework generates two different hypotheses. On the one hand, politicians may allow, encourage, or force the emigration of groups that oppose the regime as a political safety valve of sorts. This provides the government with a mechanism with which to manage potential political challengers by encouraging their exit. On the other hand, politicians—especially those in autocracies—may actively work to prevent exit because they fear the emigration of economic elites, the highly skilled, and others who have resources vital to the survival of the regime. 4

A small number of studies investigate how local-level, rather than national, political circumstances affect a potential migrant’s calculus. The limited empirical evidence currently available suggests that local conditions are substantively important determinants of the emigration decision. When individuals are highly satisfied with local amenities such as their own standard of living, quality of public services, and overall sense of physical security, they express far less intention to migrate compared with highly dissatisfied individuals (Dustmann & Okatenko, 2014 ). Furthermore, availability of public transport and access to better education facilities decreases the propensity to express an intention to emigrate (Cazzuffi & Modrego, 2018 ). This relationship holds across all levels of wealth and economic development, and there is some evidence that satisfaction with local amenities matters as much as, or even more than, income or wealth (Dustmann & Okatenko, 2014 ).

Political corruption, on both national and local levels, also has substantively important effects on potential migrants, especially those who are highly skilled. Broadly defined as the use of public office for political gain, political corruption operates as both a direct and an indirect factor promoting emigration. 5 Firstly, corruption may have a direct effect on the desire to emigrate in that it can decrease the political and economic power of an individual, leading to a lower standard of living and poorer quality of life in origin countries. If the reduction in life satisfaction resulting from corruption is sufficiently high—either by itself or in combination with other “push” factors—then the exit option becomes more attractive (Cooray & Schneider, 2016 ). Secondly, corruption also operates through indirect channels that influence other push factors. Given the large literature on how political corruption influences a number of development outcomes, it is conceivable that corruption affects the decision-making process of a potential migrant through its negative effect on social spending, education, and public health (Mo, 2001 ; Mauro, 1998 ; Gupta, Davoodi, & Thigonson, 2001 ).

The combination of its direct and indirect impacts means that corruption could be a significant part of a migrant’s decision-making process. At present there is limited work exploring this question, and the research does not yield a consensus. Some scholars argue that political corruption has no substantive effect on total bilateral migration, but that it does encourage migration among the highly skilled (Dimant, Krieger, & Meierrieks, 2013 ). This is the case, the argument goes, because corruption causes the greatest relative harm to the utility of those who have invested in human capital, who migrate to escape the negative effect on their fixed investment. In contrast, others find that a high level of corruption does increase emigration at the aggregate level (Poprawe, 2015 ). More nuanced arguments take into account the intensity of corruption: low to moderate levels of corruption lead to increased emigration of all groups, and especially of the highly skilled. But at high levels of corruption, emigration begins to decrease, indicating that intense corruption can act as a mobility constraint (Cooray & Schneider, 2016 ). All of these existing accounts, however, employ state-level measures of corruption by non-governmental organizations, such as those produced by Transparency International. Scholars have yet to harness micro-level survey data to explore the influence of personal corruption perception on the individual’s decision-making process.

The Land of Hopes and Dreams

Given that an individual has decided to emigrate, the next decision point is to choose a destination country. Advanced industrial democracies, such as those in the OECD, are major migrant-receiving countries, but so are Russia and several Gulf countries including Saudi Arabia, Qatar, and the United Arab Emirates (World Bank, 2016 ). A country’s constellation of political, economic, and social attributes is crucial to understanding an emigrant’s choice of destination. Potential migrants weigh all of these factors simultaneously when choosing a destination: will the destination allow political rights for the migrant and their children, is access to the labor market possible, and does the destination provide an opportunity for reunification with friends and family? In this section we focus on the non-economic factors that draw migrants to certain countries over others. In addition, we emphasize how skill level adds layers of complexity to a migrant’s calculus.

Political Environment, Both Formal and Informal

As noted earlier, traditional neoclassical models and their extensions place wage differentials and associated economic variables at the heart of a migrant’s choice. Gravity models posit that migrants choose a destination country based on their expected income—which itself is a function of the wage rate and the probability of finding employment in the destination—less the costs associated with moving (Ravenstein, 1885 ; Todaro, 1969 ; Borjas, 1989 ). A rigid focus on economic factors, however, blinds us to the empirical reality that a destination country’s political environment influences what destination a migrant chooses (Borjas, 1989 ). A country’s legal and political rights structure for migrants, as well as its level of tolerance for newcomers, is critical to migrants discriminating between an array of potential destinations. Fitzgerald, Leblang, and Teets ( 2014 ) argue, for example, that states with restrictive citizenship policies and strong radical right anti-immigrant parties will receive fewer migrants, while states with relatively liberal citizenship requirements and weak radical right political movements will receive more migrants. In the rational actor framework, migrants seek countries with hospitable political environments to maximize both their political representation in government and their access to labor market opportunities as a result of citizenship rights and social acceptance (Fitzgerald et al., 2014 ).

Using a broad sample of origin countries and 18 destination countries, they find that relative restrictiveness of citizenship policies and level of domestic support for the radical right are substantively important determinants of global migratory flows. Further, they find that these political variables condition a migrant’s choice of destination: the relative importance of economic factors such as the unemployment rate or the wage differential diminishes as a destination country’s political environment becomes more open for migrants. In other words, when migrants are choosing a destination country, political considerations may trump economic ones—a finding that is an important amendment to the primarily economics-focused calculus of the initial stage of the immigration decision.

However, prior to choosing and entering a destination country, a migrant must also navigate a country’s immigration policy—the regulation of both migrant entry and the rights and status of current migrants. While it is often assumed that a relatively more restrictive immigration policy deters entry, and vice versa, a lack of quantitative data has limited the ability of scholars to confirm this intuition cross-nationally. Money ( 1999 ) emphasizes that the policy output of immigration politics does not necessarily correlate with the outcome of international migrant flows. There are a number of unanswered questions in this field, including: is immigration policy a meaningful determinant of global flows of migration? Do certain kinds of immigration policies matter more than others? How does immigration policy interact with other political and economic factors, such as unemployment and social networks?

Only a handful of studies analyze whether or not immigration policy is a significant determinant of the size and character of migratory flows. Perhaps the most prominent answer to this question is the “gap hypothesis,” which posits that immigration rates continue to increase despite increasingly restrictive immigration policies in advanced countries (Cornelius & Tsuda, 2004 ). Some subsequent work seems to grant support to the gap hypothesis, indicating that immigration policy may not be a relevant factor and that national sovereignty as it relates to dictating migrant inflows has eroded significantly (Sassen, 1996 ; Castles, 2004 ). The gap hypothesis is not without its critics, with other scholars arguing that the existing empirical evidence actually lends it little or no support (Messina, 2007 ).

A more recent body of literature does indicate that immigration policy matters. Brücker and Schröder ( 2011 ), for example, find that immigration policies built to attract highly skilled migrants lead to higher admittance rates. They also show that diffusion processes cause neighboring countries to implement similar policy measures. Ortega and Peri ( 2013 ), in contrast to the gap hypothesis literature, find that restrictive immigration policy indeed reduces migrant inflows. But immigration policy can also have unintended effects on international migration: when entry requirements increase, migrant inflows decrease, but migrant outflows also decrease (Czaika & de Haas, 2016 ). This indicates that restrictive immigration policy may also lead to reduced circular migrant flows and encourage long-term settlement in destination countries.

Disaggregating immigration policy into its different components provides a clearer picture of how immigration policy may matter, and whether certain components matter more than others. Immigration policy is composed of both external and internal regulations. External regulations refer to policies that control migrant entry, such as eligibility requirements for migrants and additional conditions of entry. Internal regulations refer to policies that apply to migrants who have already gained status in the country, such as the security of a migrant’s legal status and the rights they are afforded. Helbling and Leblang ( 2017 ), using a comprehensive data set of bilateral migrant flows and the Immigration Policies in Comparison (IMPIC) data set, find that, in general, external regulations prove slightly more important in understanding migrant inflows (Helbling, Bjerre, Römer, & Zobel, 2017 ). This indicates that potential migrants focus more on how to cross borders, and less on the security of their status and rights once they settle. They do find, however, that both external and internal components of immigration are substantively important to international migrant flows.

The effects of policy, however, cannot be understood in isolation from other drivers of migration. Firstly, poor economic conditions and restrictive immigration policy are mutually reinforcing: when the unemployment rate is elevated, restrictive policies are more effective in deterring migrant flows. An increase in policy effectiveness in poor economic conditions suggests that states care more about deterring immigration when the economy is performing poorly. Secondly, a destination country’s restrictive immigration policy is more effective when migrants come from origin countries that have a common colonial heritage. This suggests that cultural similarities and migrant networks help to spread information about the immigration policy environment in the destination country. Social networks prove to be crucial in determining how much migrants know about the immigration policies of destination countries, regardless of other cultural factors such as colonial heritage or common language (Helbling & Leblang, 2017 ). In summary, more recent work supports the idea that immigration policy of destination countries exerts a significant influence on both the size and character of international migration flows. Much work remains to be done in terms of understanding the nuances of specific immigration policy components, the effect of policy change over time, and through what mechanisms immigration policy operates.

Transnational Social Networks

None of this should be taken to suggest that only political and economic considerations matter when a potential migrant contemplates a potential destination; perhaps one of the biggest contributions to the study of bilateral migration is the role played by transnational social networks. Migrating is a risky undertaking, and to minimize that risk, migrants are more likely to move to destinations where they can “readily tap into networks of co-ethnics” (Fitzgerald et al., 2014 , p. 410). Dense networks of co-ethnics not only help provide information about economic opportunities, but also serve as a social safety net which, in turn, helps decrease the risks associated with migration, including, but not limited to, finding housing and integrating into a new community (Massey, 1988 ; Portes & Böröcz, 1989 ; Portes, 1995 ; Massey et al., 1993 ; Faist, 2000 ; Sassen, 1995 ; Light, Bernard, & Kim, 1999 ). Having a transnational network of family members is quite important to destination choice; if a destination country has an immigration policy that emphasizes family reunification, migrants can use their familial connections to gain economically valuable permanent resident or citizenship status more easily than in other countries (Massey et al., 1993 , p. 450; Helbing & Leblang, 2017 ). When the migrant is comparing potential destinations, countries in which that migrant has a strong social network will be heavily favored in a cost–benefit analysis.

Note, however, that even outside of a strict rational actor framework with perfect information, transnational social networks still may be quite salient to destination choice. An interesting alternative hypothesis for the patterns we observe draws on theories from financial market behavior which focus on herding. Migrants choosing a destination observe the decisions of their co-ethnics who previously migrated and assume that those decisions were based on a relevant set of information, such as job opportunities or social tolerance of migrants. New migrants then choose the same destination as their co-ethnics not based on actual exchanges of valuable information, but based solely on the assumption that previous migration decisions were based on rational calculation (Epstein & Gang, 2006 ; Epstein, 2008 ). This is a classic example of herding, and the existing empirical evidence on the importance of transnational social networks cannot invalidate this alternative hypothesis. One could also explain social network effects through the lens of cumulative causation or feedback loops: the initial existence of connections in destination countries makes the act of migration less risky and attracts additional co-ethnics. This further expands migrant networks in a destination, further decreasing risk for future waves of migrants, and so on (Massey, 1990 ; Fussel & Massey, 2004 ; Fussel, 2010 ).

No matter the pathway by which social networks operate, the empirical evidence indicates that they are one of the most important determinants of destination choice. Potential migrants from Mexico, for example, who are able to tap into existing networks in the United States face lower direct, opportunity, and psychological costs of international migration (Massey & Garcia España, 1987 ). This same relationship holds in the European context; a study of Bulgarian and Italian migrants indicates that those with “social capital” in a destination community are more likely to migrate and to choose that particular destination (Haug, 2008 ). Studies that are more broadly cross-national in nature also confirm the social network hypothesis across a range of contexts and time periods (e.g., Clark et al., 2007 ; Hatton & Williamson, 2011 ; Fitzgerald et al., 2014 ).

Despite the importance of social networks, it is, again, important to qualify their role in framing the choice of destinations. It seems that the existence of co-ethnics in destination countries most strongly influences emigration when they are relatively few in number. Clark et al. ( 2007 ), in their study of migration to the United States, find that the “friends and relatives effect” falls to zero once the migrant stock in the United States reaches 8.3% of the source-country population. In addition, social networks alone cannot explain destination choice because their explanatory power is context-dependent. For instance, restrictive immigration policies limiting legal migration channels and family reunification may dampen the effectiveness of networks (Böcker, 1994 ; Collyer, 2006 ). Social networks are not an independent force, but also interact with economic and political realities to produce the global migration patterns we observe.

The Lens of Skill

For ease of presentation, we have up to now treated migrants as a relatively homogeneous group that faces similar push and pull factors throughout the decision-making process. Of course, not all migrants experience the same economic, political, and social incentives in the same way at each stage of the decision-making process. Perhaps the most salient differentiating feature of migrants is skill or education level. Generally, one can discuss a spectrum of skill and education level for current migrants, from relatively less educated (having attained a high school degree or less) to relatively more educated (having attained a college or post-graduate degree). The factors presented here that influence destination choice interact with a migrant’s skill level to produce differing destination choice patterns.

A migrant’s level of education, or human capital, often serves as a filter for the political treatment he or she anticipates in a particular destination country. For instance, the American public has a favorable view of highly educated migrants who hold higher-status jobs, while simultaneously having an opposite view of migrants who have less job training and do not hold a college degree (Hainmueller & Hiscox, 2010 ; Hainmueller & Hopkins, 2015 ). Indeed, the political discourse surrounding migration often emphasizes skill level and education as markers of migrants who “should be” admitted, across both countries and the ideological spectrum. 6 While political tolerance may be a condition of entry for migrants in the aggregate, the relatively privileged status of highly educated and skilled migrants in most destination countries may mean that this condition is not as salient.

While it is still an open question to what extent immigration policy influences international migration, it is clear that not all migrants face evenly applied migration restrictions. Most attractive destination countries have policies that explicitly favor highly skilled migrants, since these individuals often fill labor shortages in advanced industries such as high technology and applied science. Countries such as Australia, Canada, and New Zealand all employ so-called “points-based” immigration systems in which those with advanced degrees and needed skills are institutionally favored for legal entry (Papademetriou & Sumption, 2011 ). Meanwhile, the United States maintains the H-1B visa program, which is restricted by educational attainment and can only be used to fill jobs in which no native talent is available (USCIS). Even if destination countries decide to adopt more restrictive immigration policies, the move toward restriction has typically been focused on low-skilled migrants (Peters, 2017 ). In other words, even if immigration policy worldwide becomes more restrictive, this will almost certainly not occur at the expense of highly skilled migrants and will not prevent them choosing their most preferred destination.

Bring It on Home to Me

This article began by asserting that international labor migration is an important piece of globalization, as significant as cross-border flows of capital, goods, and services. This section argues that migrant flows enhance flows of capital and commodities. Uniquely modern conditions such as advanced telecommunications, affordable and efficient international travel, and the liberalization of financial flows mean that diasporas—populations of migrants living outside their countries of origin—and home countries often re-engage with each other (Vertovec, 2004 ; Waldinger, 2008 ). This section reviews some of the newest and most thought-provoking research on international labor migration, research that explores diaspora re-engagement and how that re-engagement alters international flows of income, portfolio and foreign direct investment (FDI), trade, and migratory flows themselves.

Remittances

As previously argued, migration is often driven by the prospect of higher wages. Rational, utility-maximizing migrants incur the cost of migration in order to earn increased income that they could not earn at home. But when migrants obtain higher wages, this additional increment to income is not always designated for individual consumption. Often, migrants use their new income to send remittances, direct transfers of money from one individual to another across national borders. Once a marginal financial flow, in 2015 remittances totaled $431 billion, far outpacing foreign aid ($135 billion) and nearly passing private debt and portfolio equity ($443 billion). More than 70% of total global remittances flow into developing countries (World Bank, 2016 ). In comparison with other financial flows such as portfolio investment and FDI, remittances are more impervious to economic crises, suggesting that they may be a countercyclical force to global downturns (Leblang, 2017 ).

Remittances represent one of the most common ways in which migrants re-engage with their homeland and alter both global income flows and distribution. Why do migrants surrender large portions of their new income, supposedly the very reason they migrated in the first place, to their families back home? New economics of labor migration (NELM) theory argues that immigration itself is motivated by a family’s need or demand for remittances—that remittances are an integral part of a family’s strategy for diversifying household financial risk (Stark & Bloom, 1985 ). Remittances “are a manifestation of informal contractual agreements between migrants and the households from which they move,” indicating that remitting is not an individual-level or purely altruistic action but rather occurs in a larger social context, that of one’s immediate or extended family (European Asylum Support Office, 2016 , p. 15).

The impact of migrant remittances on countries of origin is multifaceted yet somewhat ambiguous. Most scholarly work focuses on whether remittances positively or negatively influence existing economic conditions. A number of studies find that remittances modestly reduce poverty levels in developing countries (Adams & Page, 2005 ; Yang & Martinez, 2006 ; Acosta, Calderon, Fajnzybler, & Lopez, 2008 ; Lokshin, Bontch-Osmolovski, & Glinskaya, 2010 ). On other measures of economic well-being, such as growth, inequality, and health, the literature is quite mixed and no definitive conclusions can be drawn. For instance, some studies find that remittances encourage investment in human capital (Yang, 2008 ; Adams & Cuecuecha, 2010 ), while others find no such effect and suggest that families typically spend remittances on non-productive consumption goods (Chami, Fullenkamp, & Jahjah, 2003 ). Here we can only scratch the surface of the empirical work on remittances and economic outcomes. 7

Some of the most recent research in the field argues that remittances have a distinct political dimension, affecting regime support in developing countries and altering the conditions in which elections are held. Ahmed ( 2012 ), grouping remittances with foreign aid, argues that increased remittances allow autocratic governments to extend their tenure in office. These governments can strategically channel unearned government and household income to finance political patronage networks, which leads to a reduced likelihood of autocratic turnover, regime collapse, and mass protests against the regime. More recent research posits nearly the exact opposite: remittances are linked to a greater likelihood of democratization under autocratic regimes. Escriba-Folch, Meseguer, and Wright ( 2015 ) argue that since remittances directly increase household incomes, they reduce voter reliance on political patronage networks, undermining a key tool of autocratic stability.

Remittances may also play an important role in countries with democratic institutions, yet more research is needed to fully understand the conditions under which they matter and their substantive impact. Particularly, remittances may alter the dynamics of an election as an additional and external financial flow. There is evidence of political remittance cycles : the value of remittances spikes in the run-up to elections in developing countries. The total value of remittances to the average developing country increases by 6.6% during election years, and by 12% in elections in which no incumbent or named successor is running (O’Mahony, 2012 ). The effect is even larger in the poorest of developing countries. Finer-grained tests of this hypothesis provide additional support: using monthly and quarterly data confirms the existence of political remittance cycles, as well as using subnational rather than cross-national data (Nyblade & O’Mahony, 2014 ). However, these studies do not reveal why remittances spike, or what the effects of that spike are on electoral outcomes such as vote share, campaign financing, and political strategy.

Remittances represent a massive international financial flow that warrants more scholarly attention. While there are numerous studies on the relationship between remittances and key economic indicators, there remains much room for further work on their relationship to political outcomes in developing countries. Do remittances hasten the downfall of autocratic regimes, or do they contribute to autocratic stability? In democratic contexts, do remittances substantively influence electoral outcomes, and if so, which outcomes and how? Finally, do remittances prevent even more migration because they allow one “breadwinner from abroad” to provide for the household that remains in the homeland? While data limitations are formidable, these questions are important to the study of both international and comparative political economy.

Bilateral Trade

The argument that migrant or co-ethnic networks play an important role in international economic exchange is not novel. Greif ( 1989 , 1993 ) illustrates the role that the Maghrebi traders of the 11th century played in providing informal institutional guarantees that facilitated trade. This is but a single example. Cowen’s historical survey identifies not only the Phoenicians but also the “Spanish Jews [who] were indispensable for international commerce in the Middle Ages. The Armenians controlled the overland route between the Orient and Europe as late as the nineteenth century . Lebanese Christians developed trade between the various parts of the Ottoman empire” (Cowen, 1997 , p. 170). Rauch and Trindade ( 2002 ) provide robust empirical evidence linking the Chinese diaspora to patterns of imports and exports with their home country.

A variety of case studies document the importance of migrant networks in helping overcome problems of information asymmetries. In his study of Indian expatriates residing in the United States, Kapur ( 2014 ) documents how that community provides U.S. investors with a signal of the work ethic, labor quality, and business culture that exists in India. Likewise, Weidenbaum and Hughes ( 1996 ) chronicle the Bamboo Network—the linkages between ethnic Chinese living outside mainland China and their homeland—and how these linkages provide superior access to information and opportunities for investment.

Connections between migrant communities across countries affect cross-national investment even when these connections do not provide information about investment opportunities. In his work on the Maghrebi traders of the 11th century , Greif argues that this trading network was effective because it was able to credibly threaten collective punishment by all merchants if even one of them defected (Greif, 1989 , 1993 ). Grief shows that this co-ethnic network was able to share information regarding the past actions of actors (they could communicate a reputation)—something that was essential for the efficient functioning of markets in the absence of formal legal rules. Weidenbaum and Hughes reach a similar conclusion about the effectiveness of the Bamboo Network, remarking that “if a business owner violates an agreement, he is blacklisted. This is far worse than being sued, because the entire Chinese networks will refrain from doing business with the guilty party” (Hughes, 1996 , p. 51).

Migrants not only alter the flow of income by remitting to their countries of origin, but also influence patterns of international portfolio investment and FDI. Most existing literature on international capital allocation emphasizes monadic factors such as the importance of credible commitments and state institutional quality, failing to address explicitly dyadic phenomena that may also drive investment. Diaspora networks, in particular, facilitate cross-border investment in a number of ways. They foster a higher degree of familiarity between home and host countries, leading to a greater preference for investment in specific countries. Diaspora networks can also decrease information asymmetries in highly uncertain international capital markets in two ways. Firstly, they can provide investors with salient information about their homeland, such as consumer tastes, that can influence investment decision-making. Secondly, they can share knowledge about investment opportunities, regulation and procedures, and customs that decrease transaction costs associated with cross-border investment (Leblang, 2010 ). This place of importance for migrants suggests to the broader international political economy literature the importance of non-institutional mechanisms for channeling economic activity.

Although the hypothesized link between migrants and international investment has only recently been identified, the quantitative evidence available supports that hypothesis. Leblang ( 2010 ), using dyadic cross-sectional data, finds that diaspora networks “have both a substantively significant effect and a statistically significant effect on cross-border investment,” including international portfolio investment and FDI (p. 584). The effect of bilateral migratory flows correlates positively with the degree of information asymmetry: when informational imperfections are more pervasive in a dyad, migrants (especially the highly skilled) play a disproportionately large role in international capital allocation (Kugler, Levinthal, & Rapoport, 2017 ). Other quantitative studies find substantively similar results for FDI alone (e.g., Javorcik, Özden, Spatareanu, & Neagu, 2011 ; Aubry, Rapoport, & Reshef, 2016 ).

Many questions still remain unanswered. Firstly, does the effect of migrants on investment follow the waves of the global economy, or is it countercyclical as remittances have been shown to be? Secondly, how does this additional investment, facilitated by migrants, affect socioeconomic outcomes such as inequality, poverty, and economic development (Leblang, 2010 )? Does the participation of migrants lead to more successful FDI projects in developing countries because of their ability to break down information barriers? Within portfolio investment, do migrants lead to a preference for certain asset classes over others, and if so, what are the effects on bilateral and international capital markets? These are just a few directions in an area ripe for additional research.

Return Migration and Dual Citizenship

Besides financial flows, migrants themselves directly contribute to global flows of capital by returning to their countries of origin in large numbers. This phenomenon of return migration—or circular migration—can come in a few temporal forms, including long-term migration followed by a permanent return to a country of origin, or repeat migration in which a migrant regularly moves between destination and origin countries (Dumont & Spielvogel, 2008 ). While comparable data on return migration is scarce, some reports suggest that 20% to 50% of all immigrants leave their destination country within five years after their arrival (e.g., Borjas & Bratsberg, 1996 ; Aydemir & Robinson, 2008 ; Bratsberg, Raaum, & Sørlie, 2007 ; Dustmann & Weiss, 2007 ). An independent theoretical and empirical account of return migration does not yet exist in the literature and is beyond the scope of this paper. But in the rational actor framework, motivations to return home include a failure to realize the expected benefits of migration, changing preferences toward a migrant’s home country, achievement of a savings or other economic goal, or the opening of additional employment opportunities back home due to newly acquired experience or greater levels of economic development (Dumont & Spielvogel, 2008 ).

While most migration literature treats the country of origin as a passive actor that only provides the conditions for migration, new literature on return migration gives home country policies pride of place. Origin countries can craft policies that encourage diaspora re-engagement, incentivizing individuals to return home. Dual citizenship, for example, is an extension of extraterritorial rights, allowing migrants to retain full legal status in their home country. Dual citizenship “decreases the transaction costs associated with entering a host country’s labor market and makes it easier for migrants to return home” (Leblang, 2017 , p. 77). This leads migrants to invest their financial resources in the form of remittances back home as well as their valuable human capital. When states provide such extraterritorial rights, expatriates are 10% more likely to remit and 3% more likely to return home. Dual citizenship is also associated with a doubling of the dollar amount of remittances received by a home country (Leblang, 2017 ). These striking results suggest that in addition to the power of migrants to affect cross-border flows of money and people, countries of origin can also play a significant role.

Conclusion and Future Directions

This brief article has attempted to synthesize a broad range of literature from political science, economics, sociology, migration studies, and more to construct an account of international labor migration. To do so, the migratory process was broken down into distinct stages and decision points, focusing particularly on the decision to migrate, destination choice, and the re-engagement of migrants with their homeland. In doing so, the article also discussed the interlinkages of international migration with other fields of study in international political economy, including cross-border financial flows, trade, and investment. Through a multiplicity of approaches, we have gained a greater understanding of why people decide to move, why they decide to move to one country over another, and how and why they engage with the global economy and their homeland. Despite this intellectual progress, there remain many paths for future research at each stage of the migratory process; we highlight just a few of them here.

We know that income differentials, social ties, and local political conditions are important variables influencing the migration process. Yet the question remains: why do a small but growing number of people choose to leave while the overwhelming majority of people remain in their country of birth? Here, individual- or family-level subjective characteristics may be significant. There are a handful of observational studies that explore the relationship between subjective well-being or life satisfaction and the intention to migrate, with the nascent consensus being that life dissatisfaction increases the intention to migrate (Cai, Esipova, Oppenheimer, & Feng, 2014 ; Otrachshenko & Popova, 2014 ; Nikolova & Graham, 2015 ). But more research on intrinsic or subjective measures is needed to understand (a) their independent importance more fully and (b) how they interact with objective economic, political, and social factors. For instance, do those who are more optimistic migrate in larger numbers? Do minority individuals who feel they live in an environment in which diversity is not accepted feel a greater urge to leave home? Synthesizing these types of subjective variables and perceptions with the more prominent gravity-style models could result in a more complete picture of the international migration process.

For the “typical” migrant, one who is relatively less educated than the population in the chosen destination and does not have specialized skills, social networks are key to minimizing the risk of migrating and quickly tapping into economic opportunities in destination countries. Does this remain true for those who are highly educated? Although little empirical research exists on the topic, greater human capital and often-accompanying financial resources may operate as a substitute for the advantages offered by social networks, such as housing, overcoming linguistic barriers, and finding gainful employment. This would indicate that the “friends and family effect” is not as influential for this subset of migrants. Economic considerations, such as which destination offers the largest relative wage differential, or political considerations, such as the ease of quickly acquiring full citizenship rights, may matter more for the highly skilled. Neoclassical economic models of migration may best capture the behavior of migrants who hold human capital and who have the financial resources to independently migrate in a way that maximizes income or utility more broadly.

Since we have focused on international migration as a series of discrete decision points in this article, we have perhaps underemphasized the complexity of the physical migration process. In reality, migrants often do not pick a country and travel directly there, but travel through (perhaps several) countries of transit such as Mexico, Morocco, or Turkey along the way (Angel Castillo, 2006 ; Natter, 2013 ; Icduygu, 2005 ). There is little existing theoretical work to understand the role of transit countries in the migratory process, with much of it focusing on the potential for cooperation between destination and transit countries in managing primarily illegal immigration (Kahana & Lecker, 2005 ; Djajic & Michael, 2014 ; Djajic & Michael, 2016 ). Another related strand of the literature focuses on how wealthy destination countries are “externalizing” their immigration policy, encompassing a broader part of the migratory process than simply crossing a physically demarcated border (Duvell, 2012 ; Menjivar, 2014 ). But many questions remain, such as the following: how do we understand those who desire to enter, say, the United States, but instead relocate permanently to Mexico along the way? How do countries of transit handle the pressure of transit migrants, and how does this affect economic and political outcomes in these countries?

Finally, the focus of nearly all literature on international migration (and this article as a byproduct) implicitly views advanced economies as the only prominent destinations. However, this belies the fact that 38% of all migration stays within the “Global South” (World Bank, 2016 ). While there is certainly some literature on this phenomenon (see Ratha & Shaw, 2007 ; Gindling, 2009 ; Hujo & Piper, 2007 ), international political economy scholars have yet to sufficiently tackle this topic. The overarching research question here is: do the same push and pull factors that influence the decision to migrate and destination choice apply to those who migrate within the Global South? Do we need to construct new theories of international migration with less emphasis on factors such as wage differentials and political tolerance, or are these sufficient to understand this facet of the phenomenon? If we fail to answer these questions, we may miss explaining a significant proportion of international migration with its own consequences and policy implications.

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1. Our use of the term international labor migration follows academic and legal conventions; we use the term migration to refer to the voluntary movement of people across national borders, either in a temporary or permanent fashion. This excludes any discussion of refugees, asylum seekers, or any other groups that are forced to migrate.

2. We do not have space in this article to delve into the theoretical and empirical work unpacking the effect of demographic characteristics—age, gender, marital status, household size, and so forth on the migration decision and on subsequent flows of migrants. For comprehensive reviews, see Lichter ( 1983 ), Morrison and Lichter ( 1988 ); United Nations Population Division ( 2013 ); and Zaiceva and Zimmerman ( 2014 ).

3. Zelinsky ( 1971 ) originally identified this relationship and termed it mobility transition curve . A wealth of empirical work supports Zelinsky’s descriptive theory in a number of contexts (see Akerman, 1976 ; Gould, 1979 ; Hatton & Williamson, 1994 ; and Dao et al., 2016 ).

4. For a review of the arguments as well as some empirical tests, see Miller and Peters ( 2018 ) and Docquier, Lodigiani, Rapoport, and Schiff ( 2018 ).

5. Transparency International. “What is corruption?”

6. For example, former United Kingdom Independence Party leader Nigel Farage has called for the United Kingdom to adopt an immigration system that only allows in highly skilled migrants (“UKIP launches immigration policy”). In 2014, US President Barack Obama emphasized that he wanted to attract international students to American universities and that they “create jobs, businesses, and industries right here in America” (USA Today: “Full text: Obama’s immigration speech”). A key issue in Germany’s 2018 government formation was the creation of skill-based migration laws (Severin & Martin, 2018 ).

7. For a more comprehensive review, see Rapoport and Docquier ( 2006 ); and Adams ( 2011 ).

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Climate change is already fueling global migration. The world isn’t ready to meet people’s changing needs, experts say

TIJUANA, Mexico (AP) — Worsening climate largely from the burning of coal and gas is uprooting millions of people, with wildfires overrunning towns in California, rising seas overtaking island nations and drought exacerbating conflicts in various parts of the world.

Each year, natural disasters force an average of 21.5 million people from their homes around the world, according to the U.N. High Commissioner for Refugees. And scientists predict migration will grow as the planet gets hotter. Over the next 30 years, 143 million people are likely to be uprooted by rising seas, drought, searing temperatures and other climate catastrophes, according to the U.N.’s Intergovernmental Panel on Climate Change report published this year.

READ MORE: How climate change is hurting living things on Earth right now, according to a new report

Still, the world has yet to officially recognize climate migrants or come up with formalized ways to assess their needs and help them. Here’s a look at climate migration today.

Who are climate migrants?

Most climate migrants move within the borders of their homelands, usually from rural areas to cities after losing their home or livelihood because of drought, rising seas or another weather calamity. Because cities also are facing their own climate-related problems, including soaring temperatures and water scarcity, people are increasingly being forced to flee across international borders to seek refuge.

Yet climate migrants are not afforded refugee status under the 1951 Refugee Convention, which provides legal protection only to people fleeing persecution due to their race, religion, nationality, political opinion or particular social group.

Defining climate migration

Identifying climate migrants is not easy , especially in regions rife with poverty, violence and conflicts.

While worsening weather conditions are exacerbating poverty, crime and political instability, and fueling tensions over dwindling resources from Africa to Latin America, often climate change is overlooked as a contributing factor to people fleeing their homelands. According to the UNHCR, 90% of refugees under its mandate are from countries “on the front lines of the climate emergency.”

In El Salvador, for example, scores each year leave villages because of crop failure from drought or flooding, and end up in cities where they become victims of gang violence and ultimately flee their countries because of those attacks.

“It’s hard to say that someone moves just because of climate change. Is everyone who leaves Honduras after a hurricane a climate migrant?” Elizabeth Ferris, a research professor at the Institute for the Study of International Migration at Georgetown University, wrote in an email to The Associated Press. “And then there are non-climate related environmental hazards – people flee earthquakes, volcanic eruptions and tsunamis – should they be treated differently than those displaced by weather-related phenomena?”

Despite the challenges, it’s vital that governments identify climate-displaced people, Ferris added.

“The whole definitional issue isn’t a trivial question – how can you develop a policy for people if you aren’t clear on who it applies to?” she wrote.

International efforts

While no nation offers asylum to climate migrants , UNHCR published legal guidance in October 2020 that opens the door for offering protection to people displaced by the effects of global warming. It said that climate change should be taken into consideration in certain scenarios when it intersects with violence, though it stopped short of redefining the 1951 Refugee Convention.

The commission acknowledged that temporary protection may be insufficient if a country cannot remedy the situation from natural disasters, such as rising seas, suggesting that certain climate displaced people could be eligible for resettlement if their place of origin is considered uninhabitable.

An increasing number of countries are laying the groundwork to become safe havens for climate migrants. In May, Argentina created a special humanitarian visa for people from Mexico, Central America, and the Caribbean displaced by natural disasters to let them stay for three years.

Shortly after taking office, President Joe Biden ordered his national security adviser to conduct a months-long study that included looking at the “options for protection and resettlement of individuals displaced directly or indirectly from climate change.” A task force was set up, but so far the administration has not adopted such a program.

Low-lying Bangladesh, which is extremely vulnerable to the impacts of climate change, has been among the first to try to adapt to the new reality of migration. Efforts are underway to identify climate-resilient towns where people displaced by sea level rise, river erosion, cyclonic storms and intrusion of saline water can move to work, and in return help their new locations economically.

Transforming debates on migration

Policy debates on migration have long centered on locking down borders. Climate change is changing that.

With hundreds of millions of people expected to be uprooted by natural disasters, there is growing discussion about how to manage migration flows rather than stop them, as for many people migration will become a survival tool, according to advocates.

“One problem is just the complete lack of understanding as to how climate is forcing people to move,” said Amali Tower, founder and executive director of Climate Refugees, an advocacy group focused on raising awareness about people displaced because of climate change. “There is still this idea in the Global North (industrialized nations) that people come here because they are fleeing poverty and seeking a better life, the American Dream. In Europe, it’s the same spin of the same story. But no one wants to leave their home. We’ve got to approach climate displacement as a human security issue and not a border security issue.”

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6 Environmental Migration∗
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People who move from their homes due to climate-driven hazards are described in a range of ways, including climate migrants, environmental migrants, climate refugees, environmental refugees, and so on (Perkiss and Moerman 2018).The process of migration related to climate-driven hazards is variously described as environmental migration, environmental displacement, climate-induced migration or ...
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Doevenspeck M. 2011. "The Thin Line Between Choice and Flight: Environment and Migration in Rural Benin." International Migration 49: e50 ... Mai N. 2004. "'Looking for a More Modern Life…': The Role of Italian Television in the Albanian Migration to Italy." Westminister Papers in Communication and Culture 1 (1): 3-22. Crossref.
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A systematic review of climate migration research: gaps in existing literature

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Climate change-induced migration: a bibliometric review

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Migration types and sources of climate migrants

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