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 (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.