(A) Length scale for temperature-preserving displacement in the ocean, computed with zonal mean profiles. (B) Same, but for the continents. (C) Distributions of the shortest actual temperature-preserving migration for pixels in each 2° latitude bin of the oceans. Circles are medians, boxes are inter-quartile ranges, vertical lines are ranges, dots are outlying observations, and the black line connects mean values. (D) Same, but for continental pixels. Graphic: Hsiang and Sobel, 2016 / Scientific Reports

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.

Temperature-preserving displacements are applied to the global distribution of the people as an illustrative thought experiment, since this is one species distribution that is familiar and well documented. Actual human migrations will certainly differ and likely will be less extreme, as people can adapt and access technologies that may allow them to avoid displacement, behaviors that are abstracted away in this analysis. (A) Logarithm of the current distribution of humans. (B) The distribution of this population if all individuals undertake the displacement in Fig. 3. (C) Histogram with 1 km bins (grey, smoothed is black) for the minimum distance traveled by each person currently on Earth. Graphic: Hsiang and Sobel, 2016 / Scientific Reports

“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?

The shortest temperature-preserving migration is computed for each pixel under 2°C of global mean warming. Populations that are initially in the ocean (on land) are constrained to remain in the ocean (on land). (A) Logarithm of the minimum distance that an organism must travel to maintain the average temperature of its environment, plotted as a function of the organism's initial location. (B) The percent change in population density that occurs if a hypothetical population were initially distributed uniformly over the globe and all members of that population undertake the minimum-distance temperature-preserving displacement in (A). Graphic: Hsiang and Sobel, 2016 / Scientific Reports

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


  1. Anonymous said...

    "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."

    Who says humans are wiser then animals? I think there is ample evidence that we are not. Animals don't destroy their environment for hundreds of thousands of years. Animals don't release toxins, pollution or C02 into the atmosphere, changing the chemical balance of the oceans or atmosphere. Animals didn't invent money and enslave the rest of their species. Animals don't engage in global or regional war. Animals don't commit genocide. Animals are different then us - but we're too damned dumb to claim that we are wiser then animals.  

  2. Anonymous said...

    I agree humans are not more wise than animals. Only humans could attribute natural phenomena, to the actions of an angry/pleased god. When animals hear lightening strike, they are naturally fearful because it's sounds dangerous. What do humans think, god is angry! This is why I, unlike most visitors of this blog, do not lament the extinction of man.  

  3. Rabid Doomsayer said...

    By the end of the century. How about the next big El Nino after 2020? It will not be a case of the cost of moving it will be a case of move or die. As you have discussed before; it is wet bulb temperatures that matter most and we have already come close to that boundary.

    Far too many will wait too long, they will not leave their stuff behind until it is too late to go. Air conditioning will save the day, until the grid goes down under the load.  


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