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Climate change as an incentive for future human migration

Min Chen and Ken Caldeira · Earth System Dynamics 11, 875-883 · 2020

Key finding. Analysing today's relationship between climate and population density with all other factors held constant, climate change may within decades give hundreds of millions of people additional incentive to migrate, largely from warm tropical and subtropical countries towards cooler temperate countries, with India the country with the greatest number of people so affected.

Three world maps stacked vertically, coloured red through white to blue. The top map shows the change in population by grid cell implied for 2100, with strong red over India and West Africa and blue over northern China and parts of Europe. The middle map shows the same quantity aggregated by country, with China deep blue and India deep red. The bottom map shows the ratio of implied future to present population density, blue across Canada, northern Europe, and Russia, and red across Brazil, sub-Saharan Africa, and South and Southeast Asia.
The implied redistribution runs from warm low latitudes towards cooler high latitudes. Aggregated by country (middle), India shows the largest implied decrease and China the largest implied increase; as a ratio to present-day density (bottom), the high northern latitudes gain most and the tropics lose most. Figure 1 from Chen and Caldeira (2020), Earth System Dynamics 11, 875-883. Reproduced under CC BY 4.0. Resized for web display.

What question did this research address?

Where people live today is related, among many other things, to climate. This paper asked what today's observed relationship between climatic factors and population density implies about the future incentive to migrate, if the climate changes and everything else is held fixed.

The framing matters as much as the result. This is an "all other factors held constant" analysis, which the authors are explicit is unlikely to produce quantitatively accurate predictions. What such an analysis can offer is the order of magnitude and the spatial pattern of the incentive.

What did we find?

Applying today's climate-population-density relationships to projected future climates indicates that, within decades, hundreds of millions of people could acquire additional incentive to migrate. The direction is consistent: away from warm tropical and subtropical regions and towards cooler temperate ones.

India stands out as the country with the greatest number of people gaining additional incentive to migrate. Country-level results are strongly asymmetric, with some large temperate countries becoming relatively more attractive on this measure while large tropical and subtropical countries become less so.

The areas with the highest projected population growth rates tend to be the areas likely to be most adversely affected by climate change, so the populations gaining the most incentive to move are also the populations growing fastest.

These climate-driven incentives sit within a much broader constellation of economic, social, and political factors that motivate and constrain migration. The analysis isolates one of them; it does not predict how many people will actually move.

Why does it matter?

Treating climate as an *incentive* rather than a direct driver separates a geophysical question from a social one. The paper quantifies the scale of the pressure while leaving explicit that whether that pressure translates into movement depends on factors outside the analysis.

The order of magnitude is what carries the argument. Even granting wide uncertainty in any single number, an incentive affecting hundreds of millions of people is a different category of problem from one affecting millions.

Citation

Min Chen and Ken Caldeira (2020). Climate change as an incentive for future human migration. Earth System Dynamics 11, 875-883.

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