Migration : the effects of climate change

In the sum­mer of 2024, the Pre­sident of Indo­ne­sia inau­gu­ra­ted Nusan­ta­ra, the coun­try’s new capi­tal. The coun­try became the first to move its capi­tal for cli­mate-rela­ted rea­sons, among others : the old capi­tal, Jakar­ta, is sin­king¹ due to urba­ni­sa­tion and the pum­ping of ground­wa­ter, and the impacts – par­ti­cu­lar­ly floo­ding – are wor­se­ning as sea levels rise. In France, the expro­pria­tion and sub­sequent des­truc­tion in 2023 of Le Signal, a resi­dence in Sou­lac-sur-Mer threa­te­ned by the rece­ding coast­line, has left its mark on peo­ple’s minds. The cli­mate – and its evo­lu­tion – is pushing men and women to move around the pla­net. In 2023, more than 26 mil­lion inter­nal dis­pla­ce­ments were recor­ded due to natu­ral disas­ters, par­ti­cu­lar­ly floods and storms, accor­ding to the 2024 World Report on Inter­nal Displacement.

Katrin Mil­lock. There are many fac­tors that deter­mine migra­tion : eco­no­mic, social, poli­ti­cal, demo­gra­phic and cultu­ral. Wea­ther condi­tions can affect each of these fac­tors. For example, a hur­ri­cane can come as a shock to people, and lead to a drop in income, which in turn trig­gers migration.

Cli­mate change has both direct and indi­rect effects on migra­tion. The most obvious direct effect is the des­truc­tion of pro­per­ty during extreme wea­ther events, which often leads to tem­po­ra­ry dis­pla­ce­ment. Ano­ther direct effect is the reduc­tion in agri­cul­tu­ral pro­duc­ti­vi­ty because of drought : in coun­tries where a large pro­por­tion of the popu­la­tion depends on agri­cul­ture for their live­li­hood, this leads to a reduc­tion in income and the­re­fore to migra­tion. Final­ly, the direct effects of cli­mate change – such as increa­sed cir­cu­la­tion of vec­tor-borne diseases – can make cer­tain regions uninhabitable.

One of the indi­rect effects recor­ded is the impact on the eco­no­my. It has been obser­ved that those who migrate are not always the people direct­ly affec­ted. For example, the price of a crop affec­ted by drought may rise and this increase in price may cause consu­mers to migrate.

Cli­mate change has seve­ral dif­ferent impacts on migra­tion. There is no single ans­wer ; it depends very much on the local context. We know, for example, that the com­po­si­tion of migra­to­ry flows will be affec­ted in the future. While today we tend to see the move­ment of men of wor­king age, extreme cli­ma­tic events will lead to dis­tress migra­tion, i.e. when whole fami­lies move. Many stu­dies also show that extreme events tend to be asso­cia­ted with tem­po­ra­ry move­ments over short dis­tances, often within the same coun­try. Conver­se­ly, slow-onset phe­no­me­na such as deser­ti­fi­ca­tion tend to create per­ma­nent migra­to­ry flows. In India² and Afri­ca³, various stu­dies have shown that urba­ni­sa­tion is indu­ced by rising tem­pe­ra­tures, but only for cities with a trans­port net­work and employ­ment oppor­tu­ni­ties in sec­tors other than agri­cul­ture. But as the Inter­go­vern­men­tal Panel on Cli­mate Change (IPCC) points out in its latest report⁴, there are still many uncer­tain­ties about the impact of cli­mate change on migra­to­ry flows.

It is dif­fi­cult to sepa­rate the impact of cli­mate change from other migra­tion fac­tors. Cli­mate change inter­acts with social fac­tors : for example, stu­dies show that poli­ti­cal ins­ti­tu­tions are dependent in the long term on our envi­ron­ment and on cli­mate change. Howe­ver, they them­selves influence migra­tion processes.

The second obs­tacle is metho­do­lo­gi­cal. To iso­late the impact of cli­mate change, we need to ensure that other fac­tors remain constant. Howe­ver, cli­mate change is a long-term pro­cess, during which the other fac­tors will also evolve. To over­come this dif­fi­cul­ty, most stu­dies focus on extreme wea­ther events, which are almost ins­tan­ta­neous pro­cesses. But these stu­dies do not allow us to ful­ly assess the effects of cli­mate change.

There are also data pro­blems : in cli­ma­to­lo­gy, the impact of cli­mate change is consi­de­red to be visible over a per­iod of at least 30 years, and often more. Yet socio-eco­no­mic data often covers shor­ter per­iods. We don’t even have refe­rence data from before cli­mate change : the oldest com­plete data on inter­na­tio­nal migra­tion only dates back to 1960.

To my know­ledge, only two stu­dies pro­vide robust results. In Science, two authors use asy­lum appli­ca­tions in the Euro­pean Union to assess the impact of rising tem­pe­ra­tures in sou­thern coun­tries⁵. They note that bet­ween 2000 and 2014, asy­lum appli­ca­tions increa­sed when tem­pe­ra­tures moved away from an opti­mum of around 20°C – the opti­mum tem­pe­ra­ture for agri­cul­ture. They esti­mate that claims could increase by 28% (i.e. around 100,000 extra claims per year) by 2100 for an ave­rage green­house gas emis­sions sce­na­rio (RCP 4.5). In 2022, in the Jour­nal of the Euro­pean Eco­no­mic Asso­cia­tion⁶, ano­ther team esti­mates the num­ber of addi­tio­nal cli­mate migrants (of wor­king age) by the end of the cen­tu­ry at 45, 62 or 97 mil­lion (depen­ding on future green­house gas emis­sion sce­na­rios). Even if the pro­jec­tions are quan­ti­fied, these results should be consi­de­red as orders of magni­tude, given the uncer­tain­ties involved.

That depends very much on how cli­mate change mani­fests itself. The small islands of the Paci­fic, for example, are the har­dest hit by rising sea levels. South-East Asia is main­ly threa­te­ned by floo­ding, while popu­la­tion flows around the Medi­ter­ra­nean, West Afri­ca and Asia will be affec­ted by drought and extreme tem­pe­ra­tures. Migra­tion lin­ked to fal­ling agri­cul­tu­ral pro­duc­ti­vi­ty will tend to affect South and Cen­tral Ame­ri­ca and parts of Afri­ca. Final­ly, the demo­gra­phic fac­tor is a major deter­mi­nant of migra­to­ry flows, and it will be pre­do­mi­nant in Afri­ca in the future.

We also know that it is the weal­thiest hou­se­holds that have the resources to migrate. The poo­rest hou­se­holds are trap­ped in place, and stu­dies show that cli­mate change will lead to increa­sed inequa­li­ty, pover­ty and mor­ta­li­ty for those who do not have the oppor­tu­ni­ty to leave. It is cru­cial that inter­na­tio­nal bodies take these immo­bile popu­la­tions into consideration.

Interview by Anaïs Marechal

Find out more : 

• Benon­nier, T., K. Mil­lock and V. Taraz. “Long-term Migra­tion Trends and Rising Tem­pe­ra­tures : The Role of Irri­ga­tion”, Jour­nal of Envi­ron­men­tal Eco­no­mics and Poli­cy 11(3), 307–330, 2022.
• Becer­ra-Val­bue­na, L. and K. Mil­lock. “Gen­de­red Migra­tion Res­ponses to Drought in Mala­wi”, Jour­nal of Demo­gra­phic Eco­no­mics 87(3), 437–477, 2021.
• Cat­ta­neo, C., M. Beine, C. Fröh­lich, D. Kni­ve­ton, I. Mar­ti­nez-Zar­zo­so, M. Mas­tro­rillo, K. Mil­lock, E. Piguet and B. Schra­ven. “Human Migra­tion in the Era of Cli­mate Change”, Review of Envi­ron­men­tal Eco­no­mics and Poli­cy 13(2), 189–206, 2019.