Claim: Global Warming will Cause Extreme Tropical Population Shifts

Guest essay by Eric Worrall

A new study has just been published which claims a few degrees global warming will cause extreme population migrations in the tropics. But their model makes a rather questionable assumption about tropical climates.

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.

Read more: http://www.nature.com/articles/srep25697

The reasoning is, since the tropics has a very mild temperature gradient, if global warming causes tropical temperatures to rise slightly, people will have to migrate long distances to find their old temperature range.

From the study;

… Near the equator, the horizontal component of the Coriolis force becomes weak due to the small projection of the earth’s rotation vector on the local vertical. As a consequence tropical pressure and temperature gradients are much smaller than extratropical ones. Perusal of global maps of temperature on a surface of constant altitude show much larger variations at high latitudes than low, no matter what season, year, or time-averaging period is chosen. Because of this, the displacement distance L is necessarily larger in the tropics than in the extratropics, sometimes dramatically so. …

Read more: Same link as above

The flawed reasoning behind this assumption is people in the tropics are already on the brink of unsurvivable heat, that a small shift in average temperatures would push people over the edge. This is simply not true. In the tropics we have a technological innovation which allows us to mitigate the distress we would otherwise experience on hot days, called air conditioning. Or cheap ceiling fans, if you can’t afford air conditioning. When we have to go out in the blazing sun, we wear hats and dark glasses. Sometimes we even plant trees to provide more shade. On really hot days we sit in the swimming pool, drink beer and consume charred animal flesh.

People who choose to live in the tropics don’t mind when the thermometer soars above 90F – thats why we moved here, we enjoy that kind of weather.