Millions On the Move? Unpacking the Climate-Migration Nexus
In 2022, the global community hosted a series of extreme weather events. In spring, heatwaves in Pakistan brought temperatures above 40 °C for extended periods of time in large parts of the country. In summer, heavy rainfall—intensified by the preceding heatwaves—flooded around one-third of the country. Consequently, more than 1,200 people were killed and an estimated 32 million were displaced. In that same year, cyclone Megi displaced around 900,000 people in the Philippines, droughts displaced 1.1 million people in Sudan and ravaging wildfires displaced more than 200,000 people in the United States. With such extreme events becoming more frequent, the debate around climate change is shifting from its long-term, far-future effects to the present and the near-future ones. Already today and progressively more so in the future climate change increases the intensity, duration and frequency of many atmospheric, hydrologic and biologic hazards. This calls attention to an in-depth analysis of patterns of climate-induced migration, which is no longer a problem of the future, but a challenge for today.
Considering the large number of people displaced due to recent disasters and the projected effects of climate change, the outlook on future climate-induced migration appears dire. What if the hundreds of millions of people whose livelihoods will be compromised by climate change decide to pack their things and move to the Global North? Such narratives are used by populist parties and movements in order to elicit support for stricter immigration laws. But are we really facing mass migration flows of an unprecedented scale to best start preparing now?
As with most complex questions, the answer is neither a clear “yes” nor a clear “no”. In recent years, various studies have tried to project the number of climate-induced migrants. Most recently, the World Bank published the Groundswell reports, estimating that by the year 2050, climate change could force more than 216 million people to migrate within their countries  in low- and moderate-income regions. This scenario is equivalent to the entire population of France, England and Germany shifting residence over the course of the next 30 years.
The reality, however, is more complex than a single number. Many studies projecting the number of climate-induced migration mainly consider how many people live in areas that will be affected by climate change effects like sea-level rise, floods or droughts.  The underlying assumption is that all these people will be forced to move once climate change impacts materialize. In situations that present an immediate danger to life—like Pakistan’s 2022 floods or sea-level rise submerging land—people indeed need to “flee to save their lives”. In other cases, however, people might develop technological or cultural adaptation strategies that allow them to remain in situ despite climatic changes materializing. In drought-affected areas, for instance, people might plant more drought-resistant crops or irrigate their fields instead of solely relying on rainfed agriculture. In flood-prone regions, people might raise their houses to reduce damages if water levels rise. This implies that existing studies might overestimate the number of climate migrants if they do not consider adaptation options, while at the same time hindering evidence-based policymaking to further support in situ adaptation strategies.
Besides options to adapt in situ, migration decision-making is influenced by a variety of factors extending beyond the mere push-logic of environmental stress. Imagine a farmer’s family living next to a river in Bangladesh, whose land and house are flooded each year during the monsoon season. Many factors can influence whether they stay where they are or whether they move away: does the government provide support to compensate for the lost crops? Does the family have the financial means to shift their household elsewhere? Do they have friends in the nearest town who might assist the breadwinner in finding a new job? There are many questions that play into major life choices within the context of climate change.
To structure the variety of factors that influence migration decision making as in the example above, Black et al’s seminal conceptual framework points to three levels that play a role in the environment-migration nexus. At the macro-level, factors such as the political system or the economic situation of a country might affect the resources available to a family considering migration. The meso-level, like migrant networks or legal frameworks, impacts how easily the family could move. And also micro-level factors, such as gender or education, can influence these decisions. In this framework, environmental change can influence migration choices directly by affecting ecosystem services or hazard exposure. Likewise, it can also have indirect effects by acting on factors such as the economic system, for instance, when a flood damages roads, hindering transportation, or on a household’s assets, for example, when a storm destroys a household’s crops, causing hunger.
Ultimately, environmental and climatic changes are just one among many factors in the migration decision making process. Establishing a causal link between environmental changes and migration is thus extremely challenging. Further, estimating more precise numbers concerning future climate migration requires considering the complexities behind migration decision making.
One way to improve projections of climate-induced migration is to incorporate findings from empirical research. However, a significant share of the evidence gathered so far is derived from aggregated levels of analysis.  This means that such studies link geo-temporal climate data to aggregate migration datasets,  for instance connecting data for a drought that has occurred in one part of a country to migration data gathered from a nation-wide census. While such an approach can generate valuable insights, it bears the danger of “ecological fallacy”: even if, for instance, inter-provincial migration increases in the aftermath of a drought, this does not necessarily mean that the drought was indeed the primary reason motivating people to move.
To overcome this challenge inherent to aggregate-level analyses, we need more rigorous research on the micro-level processes and the individual perceptions of environmental changes underlying migration decision making to further our understanding of climate-induced migration.
One example of a study that aims at providing credible micro-level evidence on the causal link between environmental changes and migration is the project “Climate risk, land loss, and migration: Evidence from a quasi-experiment in Bangladesh”, conducted by researchers from ETH Zurich, including the author of this article. In this longitudinal study, a population at risk of riverbank erosion and floods is interviewed periodically over three years. What makes this endeavor unique is that the respondents are interviewed first before they have been affected by environmental shocks. After experiencing the effects of environmental change, the same people are re-interviewed, both those affected and those who were not, as well as those who migrated and those who stayed. This constitutes a great improvement over existing micro-level studies that often interview migrants only retrospectively after an environmental shock, asking them about their reasons to migrate. In their responses, migrants often state economic reasons such as unemployment or hunger as the primary reasons for migrating. Economic struggles can, however, be caused by an environmental shock like a drought or a storm. Retrospective studies might then mask the full influence of environmental shocks on migration decision making, and hence underestimate their effect.
Another aspect that existing studies fail to address adequately are people’s aspirations to migrate, identifying whether they prefer moving away to staying put. Intuitively, one might think that people want to leave areas vulnerable to environmental shocks. Accordingly, it is often assumed that those who stay in exposed areas do so because they lack the ability to migrate, such as resources to shift their house or a migrant network, and thereby become “trapped” in locations at risk. While the concept is of interest in both policy and academic circles, the debate often neglects that many people prefer to stay put. Evidence from different countries suggests that people might prefer adapting in situ over relocating if they have a choice. Many people experience strong attachments to their homes, or possess material motivations such as land ownership. Motivation to stay may have non-material components such as social, emotional and spiritual ties. As with migration decisions, immobility behavior can only be fully understood if people’s perceptions on the ground are captured holistically.
More rigorous micro-level studies on environmentally induced migration are needed to fully understand the present global situation. Studies as the above-mentioned project in Bangladesh can lead the way in appropriate methodology. Since the linkages between environmental changes and migration are highly context-specific, individual studies cannot easily be generalized and transferred to other settings. Conducting comparable studies in different contexts will allow for a more holistic understanding of the environment-migration nexus.
Simplistic perspectives on climate migration necessitate caution. Narratives around climate-induced mass migration or populations becoming “trapped” by climate change have the potential to generate public interest. And yet, they mask a reality that is oftentimes much more complex and nuanced than a simple, generalizing statement. Yes, climate change will alter migration patterns and yes, it has the potential of exacerbating pre-existing vulnerabilities of populations-at-risk. Still, it is imperative to keep in mind that the exact nature of climate-induced migration will depend on the local context and the agency of all parties involved. No research or policy on climate-induced migration can capture the full picture or design sustainable solutions without taking these aspects into consideration.
Jan Freihardt recently completed his PhD at the Chair for International Political Economy and Environmental Politics at ETH Zurich. In his PhD, he researched environmental (im)mobility under the project “Climate Risk, Land Loss, and Migration: Evidence from a Quasi-Experiment in Bangladesh”, funded by the Swiss National Science Foundation. Jan holds two master's degrees from ETH, one in Environmental Engineering and one in Science, Technology and Policy.
 Mallapaty, S. (2022). Why are Pakistan's floods so extreme this year? Nature. Advance online publication. https://doi.org/10.1038/d41586-022-02813-6
 IDMC (2023). 2023 Global Report on Internal Displacement. Internal Displacement Monitoring Center (IDMC). Geneva, Switzerland.
 IPCC. (2021). Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change (In Press). Cambridge University Press. https://doi.org/10.1017/9781009157896
 Missirian, A., & Schlenker, W. (2017). Asylum applications respond to temperature fluctuations. Science, 358(6370), 1610–1614. https://doi.org/10.1126/science.aao0432
 Clement, V [Viviane], Rigaud, K. K [Kanta Kumari], Sherbinin, A. de [Alex], Jones, B [Bryan], Adamo, S [Susana], Schewe, J [Jacob], Sadiq, N., & Shabahat, E. (2021). Groundswell Part 2: Acting on Internal Climate Migration. World Bank.
 Rigaud, K. K [K. K.], Sherbinin, A. de [A.], Jones, B [B.], Bergmann, J., Clement, V [V.], Ober, K., Schewe, J [J.], Adamo, S [S.], McCusker, B., Heuser, S., & Midgley, A. (2018). Groundswell: Preparing for Internal Climate Migration. Washington, DC. The World Bank.
 Kam, Pui M., Gabriela Aznar-Siguan, Jacob Schewe, Leonardo Milano, Justin Ginnetti, Sven Willner, Jamie W. McCaughey, and David N. Bresch. 2021. “Global warming and population change both heighten future risk of human displacement due to river floods.” Environmental Research Letters 16 (4): 44026.
 Hauer, Mathew E., Elizabeth Fussell, Valerie Mueller, Maxine Burkett, Maia Call, Kali Abel, Robert McLeman, and David Wrathall. 2020. “Sea-level rise and human migration.” Nature Reviews Earth & Environment 1 (1): 28–39.
 Warner, K. (2010). Global environmental change and migration: Governance challenges. Global Environmental Change, 20(3), 402–413.
 Elum, Z. A., Modise, D. M., & Marr, A. (2017). Farmer’s perception of climate change and responsive strategies in three selected provinces of South Africa. Climate Risk Management, 16, 246–257. https://doi.org/10.1016/j.crm.2016.11.001
 Marfai, M.A., Sekaranom, A.B. & Ward, P. (2015) Community responses and adaptation strategies toward flood hazard in Jakarta, Indonesia. Nat Hazards 75, 1127–1144. https://doi.org/10.1007/s11069-014-1365-3.
 Black, R., Adger, W. N., Arnell, N. W., Dercon, S., Geddes, A., & Thomas, D. (2011). The effect of environmental change on human migration. Global Environmental Change, 21, S3-S11. https://doi.org/10.1016/j.gloenvcha.2011.10.001.
 Thiede, B., Gray, C., & Mueller, V. (2016). Climate variability and inter-provincial migration in South America, 1970‐2011. Global Environmental Change, 41, 228–240.
 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, 10(10), 904–912. https://doi.org/10.1038/s41558-020-0898-6
 Piguet, E. (2010). Linking climate change, environmental degradation, and migration: a methodological overview. Wiley Interdisciplinary Reviews. Climate Change, 1(4), 517–524. https://doi.org/10.1002/wcc.54.
 “Climate Risk, Land Loss, and Migration: Evidence from a Quasi-Experiment in Bangladesh”, Swiss National Science Foundation, accessed September 13, 2023, https://data.snf.ch/grants/grant/185210.
 Koubi, V., Spilker, G., Schaffer, L., & Böhmelt, T. (2016). The role of environmental perceptions in migration decision-making: evidence from both migrants and non-migrants in five developing countries. Population and Environment, 38(2), 134–163. https://doi.org/10.1007/s11111-016-0258-7.
 Koubi, V., Schaffer, L., Spilker, G., & Böhmelt, T. (2022). Climate events and the role of adaptive capacity for (im-) mobility. Population and Environment, 1–26.
 Seebauer, S., & Winkler, C. (2020). Should I stay or should I go? Factors in household decisions for or against relocation from a flood risk area. Global Environmental Change, 60, 102018. https://doi.org/10.1016/j.gloenvcha.2019.102018.
 Mallick, B., Sultana, Z., & Bennett, C. M. (2020). How do sustainable livelihoods influence environmental (non-)migration aspirations? Applied Geography, 124, 102328. https://doi.org/10.1016/j.apgeog.2020.102328