The Climate-Migration Nexus Introduces New Political Risks

How do people react as their livelihoods slip away from them? It’s a question not often asked, but the answer may be more apparent than we realize. The nightly news is saturated with images of small boats making the treacherous journey across the Mediterranean to Europe, or of caravans on a perilous desert odyssey to cross the U.S.-Mexico border.

Irregular migration is a dangerous venture. What motivates people to take such profound risks in search of a better life?

The worsening effects of climate change may be at play—and they’re only getting worse. As climate change impacts societies across the world—but hitting hardest the Global South—an emerging climate-migration nexus weaves together the pressing security challenges of a changing environment and the mass movement of people.

This could have enormous policy implications for the world, and for the United States and Europe in particular. But a lack of data has stood in the way of research that addresses this nexus from a global perspective.

Understanding climate and migration together is critical for allowing us to prepare for what comes next. So far, our work is finding that climate disruptions are going to become much larger than they have been in the past, with severe consequences for international migration. There is an urgent need for improved global governance on this issue, requiring much greater international coordination.

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The year 2024 marks a grim milestone: humanity is crossing the 1.5 degree Celsius threshold of industrial-era global average temperature rise, the outcome the Paris Climate Accords were meant to help stop. As the planet warms, natural disasters are proliferating—a report published this month for the International Chamber of Commerce found that over the last decade, climate-induced extreme weather events cost the world a staggering $2 trillion. In the last two years, damages rose nearly 20 percent over previous eight.

The trends are alarming—and poised to get much worse.

The growing climate-migration nexus is going to affect everyone, in rich and poor countries alike. To prepare for the potential risks, we need to better understand the trajectory of how climate change is influencing migratory patterns.

The nations most vulnerable to climate impacts are also the least developed. In this context, it’s intuitive that people would try to move to richer, more resilient places. The growing climate-migration nexus is going to affect everyone, in rich and poor countries alike. To prepare for the potential risks, we need to better understand the trajectory of how climate change is influencing migratory patterns.

To do this we needed data on climate and data on migration—and both at a global level. The former is easy to come by; we have reams of data on the climate and how it has changed over time. But the latter is much harder.

In the past, most studies on environmentally driven migration looked at it within countries. Bangladesh, where 7.1 million people have been internally displaced by natural disasters as of 2022, is a notable case study.

But there have been fewer cross-border studies—and those that do exist have relied on less data-intensive approaches. That’s because it’s been hard to quantify how many people are moving and why.

Migration data are traditionally based on rough estimates of population change within countries, which provides an incomplete picture. For example, we can see in census data that a country is losing population or that the rate of population growth is slowing, but that’s not enough to determine migration flows. Those changes may be due to migration, but could also be from shifting mortality or fertility rates—we wouldn’t necessarily know.

But we have to know—the costs of not knowing are high. The humanitarian toll of irregular migration is serious; more than 8,000 people have died trying to cross the U.S.-Mexico border since 1998, and 28,000 people have died or gone missing in the Mediterranean since 2014.

The impact on destination countries is also significant, albeit in a different way. Fears related to migration have been instrumental in the rise of right-wing populism in Europe. The desire to better control borders was the decisive issue in the 2016 Brexit referendum, and was also prominent in recent U.S. elections. The reaction to climate-induced migration poses risks for the general health of democratic institutions across the West.

There is much we do not know, but need to. That’s because the issue of migration is host to a complex variety of variables.

Bad weather one year is not enough to get people to pack up their lives and move. The climate has to consistently worsen, making a place inhospitable or expected to become so over time. This could mean four years to a decade of droughts or extreme rainfall before individuals decide to migrate. Trends are important too—would-be migrants might see how temperatures are not just hot this year, but getting hotter and hotter every year.

Another variable is the ability to migrate. One might be willing to move but lack the resources to do so, especially if climate change has harmed one’s livelihood. On the other hand, those with more resources might not need to migrate, because they have the capacity to buy air conditioning for their house or a new irrigation system for their farm.

When someone finally decides to migrate, the next decision is where to go. Because agricultural livelihoods are the most vulnerable to climate change, you might first see people leaving rural areas for cities within the same country. But over time, internal migratory pressures can strain urban resources, pushing people toward cross-border migration.

To understand the cause and effect between these push and pull factors, we need migration data to be as granular as possible. Researchers are trying to think of innovative ways to do this, like using social media to find people logging on from different grid cells on a world map. But while this could be useful for measuring present migration, it tells us nothing about historical trends. And we also need to consider empirical methods, like the kinds and combinations of climate metrics that affect whether people choose to move or not.

Getting the data right is crucial for enabling solutions, both at the level of states and globally. The cross-border nature of the problem means that nations cannot go it alone. There needs to be solid coordination between origin states, transit states, and destination states. And getting the policy right requires solid interdisciplinary research to provide actionable information and analysis.

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We started at the UC San Diego School of Global Policy and Strategy in 2016 and 2017, working on climate and migration respectively. Kate had been an interdisciplinary climate scientist who worked on a number of topics but was intimidated by tackling the complexities of migration decisions. Gaurav had cut his teeth in development economics and had wondered how climate change would impact the world’s most vulnerable people. A couple of interesting discussions over coffee motivated us to work together to see if we could figure out a way to predict where climate change-induced migration might happen and why.

In the end, choosing to migrate is a very drastic and complicated decision. Our approach aims to dive deeper into what influences that choice.

Our work looks at climate-induced migration on a global scale. We use a two-step process: we’ve created a data-based model for internal migration like some of the studies that have come before us, and then translate that into international flows.

Policymakers are hungry for information about how climate will affect migration. They know it’s going to be a problem that policy will have to contend with. There’s a lot of uncertainty right now, but also a desire to prepare for what’s coming based on information and evidence.

To the extent that our work can advance knowledge in this area even a little, it will have a high impact. We don’t have all the information just yet. A lot of the challenges are not things that are our research will solve today. But we can at least help inform policymakers in trying to quantify how serious and urgent this is going to be. That’s the primary goal here—but there’s a lot more work to be done by climate and social scientists across the world.

Kate Ricke and Gaurav Khanna are assistant professors at UC San Diego and researchers for the IGCC-funded project Sea Level Rise-Driven Migration Under Varied Institutional Constraints. This commentary was adapted from a conversation Kate and Gaurav had with IGCC’s senior writer/editor Paddy Ryan.

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