If global warming empties India – ‘The rapid evacuation of the tropics would cause migrants to concentrate in tropical margins and the subtropics, where population densities would increase by 300 percent or more’

Desdemona Despair

By Gayathri Vaidyanathan
9 June 2016

(ClimateWire) – In an armchair experiment where humans are thought of as no wiser than animals, scientists have found that climate change could empty some nations by 2100.

A warming of 2 degrees Celsius would cause 34 percent of the world’s population to migrate more than 300 miles, to places on the fringes of the tropics where the temperatures are milder. Dramatic population declines might occur in Mexico, Central America, Africa, and India. The results were published today in Scientific Reports.

The scientists are cautious about the predictive power of their thought experiment, particularly as it relates to humans. People, unlike animals, can adapt to higher temperatures through technologies such as air conditioning. They also face barriers to long-distance migration, such as land borders, language barriers or even buying an air ticket. The scientists stressed that they are only exploring a hypothetical response to rising temperatures.

“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,” Adam Sobel, a professor of applied physics and math at Columbia University and a co-author of the study, said in a statement.

Some of the regions that the study suggests would be worst affected currently have the lowest migration rates in the world, said Valerie Mueller, a senior research fellow who studies migration at the International Food Policy Research Institute.

“They try to cast this paper as a way of thinking about not just human, but the migration of other species,” she said. “For birds that have very little costs in moving 500 and 1,000 kilometers [300 to 620 miles], it might work. But this framework for monitoring human migration doesn’t recognize the formidable barriers we face in moving.” [more]

What If Global Warming Emptied India?

ABSTRACT: 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.

Potentially Extreme Population Displacement and Concentration in the Tropics Under Non-Extreme Warming