In March, US media reported on two groups who could claim the title of the country’s first “climate refugees” — a Native American tribe in Louisiana and a coastal community in Alaska. Both communities are planning to relocate away from land that is disappearing. They are not alone. A few other communities — notably the island nation of Kiribati — are considering whether the full relocation of people threatened by climate change is necessary and how to plan for it. Whether planned or not, migration movements caused in whole or in part by climate change will be part of the future. A 2016 report by the US National Intelligence Council highlighted what many other researchers have also noted: “Over 20 years, the net effects of climate change on the patterns of global human movement and statelessness could be dramatic, perhaps unprecedented.” While people have long migrated in response to climatic events, today’s anthropogenic form of climate change will require new, faster adaptations than humans have long practiced. Scientists can rarely definitively link climate change to a single weather or climate event. However, it is clear that climate change will shift weather patterns in many parts of the world, intensify storms, prolong and increase dry and rainy periods, and raise sea levels. These changes are very likely to accelerate existing migration patterns and to create new ones. Climate change migrants leave their homes due to the direct or indirect effects of climate change — or a mixture of the two. Drought, desertification and increased flooding can directly undermine an agricultural area’s ability to produce sufficient food, leading people to move elsewhere, often to cities, in search of food and work. For example, climate change appears to have worsened drought and desertification in the western African Sahel, causing migrations away from drying areas, which in turn fed into political instability. Similarly, the effects of climate change can damage marine resources, forcing communities that rely on fishing or aquaculture to move. Another way in which climate change effects can lead directly to migration is in cases where severe flooding or extreme weather events, such as hurricanes or cyclones, become so regular or so dramatic that communities in the way of storms and floods must leave. For example, after Hurricane Maria destroyed much of the infrastructure and badly damaged the economy of Puerto Rico when it hit in 2017, the island has experienced a dramatic acceleration in migration to the mainland United States. As climate patterns shift, these situations can occur even in places that previously did not regularly experience destructive storms, as seen with the two unprecedented cyclones that hit Yemen in 2015. Whether planned or not, migration movements caused in whole or in part by climate change will be part of the future. Kerry Boyd Anderson In other cases, future rises in sea levels will so badly damage coastal communities through land loss, erosion, increased storm surges and tides, and saltwater intrusion into freshwater sources that the communities will have to move. This is already happening — or threatening to happen soon — to communities ranging from Kiribati and Fiji to Alaska and Louisiana, plus probably many more further into the future. Climate change can also contribute to migration flows in indirect ways. It can worsen economic problems and lead to increased food prices, which might reinforce existing economic migration patterns. Multiple studies have demonstrated how climate change can exacerbate conflict, including the record-breaking drought that led to rural-to-urban migration in Syria, which likely contributed to — though was not the sole cause of — the Syrian civil war. The Syrian case is an instructive example of how global climate change worsened a local climate event and led to internal migration within a country that contributed to instability, then a war that led to large-scale refugee flows. These are the types of trends that many experts believe will become more common as climate change intensifies in the future. The Syrian case also highlights the movement of people from rural areas to cities. Urbanization is a global trend that is occurring for many reasons, but climate change will likely accelerate it in some parts of the world. This will pose major challenges for many cities, especially as most of the world’s major urban centers are located on or near coastlines and thus are also vulnerable to the future effects of climate change. Large-scale movements of vulnerable populations within and between countries will pose new national security, urban planning, governance and humanitarian challenges. International institutions and national and local governments should plan now, including investing in efforts to adapt to climate change and prepare for demographic shifts. At-risk communities should consider how to increase resiliency and, in some cases, potentially relocate. Some experts have also said there should be a new treaty to protect people fleeing their homes due to climate change, providing them with a clear definition under international law. Many people who migrate due to climatic changes fall between the cracks of current international legal definitions. In most cases, they are not refugees who have fled their country to escape persecution or violence, which would give them special protected status under international law. However, those fleeing climate events are not really voluntary migrants who move in search of economic opportunities. A clear definition of a climate change refugee and new treaty structures for how states might manage such migration could lay the foundation for a more effective international response in the future. Planning ahead and developing new tools for coordination between institutions and governments would help reduce the risk of future instability caused by climate change-fueled migration. At the same time, policymakers will have to accept a large dose of uncertainty in exactly how such migration will play out. Kerry Boyd Anderson is a writer and political risk consultant with more than 14 years’ experience as a professional analyst of international security issues and Middle East political and business risks. Her previous positions include deputy director for advisory with Oxford Analytica and managing editor of Arms Control Today. Twitter: @KBAresearch