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.