Evidence increasingly suggests that as climate warms, some plant, animal, and human populations may move to preserve their environmental temperature. The distances they must travel to do this depends on how much cooler nearby surfaces temperatures are. Because large-scale atmospheric dynamics constrain surface temperatures to be nearly uniform near the equator, these displacements can grow to extreme distances in the tropics, even under relatively mild warming scenarios. Here we show that in order to preserve their annual mean temperatures, tropical populations would have to travel distances greater than 1000 km over less than a century if global mean temperature rises by 2 °C over the same period. The disproportionately rapid evacuation of the tropics under such a scenario would cause migrants to concentrate in tropical margins and the subtropics, where population densities would increase 300% or more. These results may have critical consequences for ecosystem and human wellbeing in tropical contexts where alternatives to geographic displacement are limited.Kathleen Maclay reports on the story in Climate change could trigger tropical evacuations, researchers advise Berkeley News 06/09/2016:
“We’re not making specific predictions about migration patterns of individual species, but the geophysical constraint is that, as the tropics get hotter, you’ll have to go far, essentially leaving the tropics, to cool off,” said Sobel.
Because the tropics are uniformly hot, when things get hotter by just a small amount, populations will have to move far to find relief.
Hsiang explains it with an analogy: “Imagine you have a fixed budget you can spend on your apartment and rents are the same throughout your entire neighborhood. If all the rents go up, even by just a little bit, you might have to move very far to find a new place you can afford.”
Hsiang and Sobel describe climate-related displacements in the tropics as “an almost complete evacuation of the equatorial band” that could impact ecosystems as well as human well-being.