Will hotter temps cause a mass exodus from the tropics?

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Scientists say it won’t take much of a global warm-up to force a migration of plants, animals, and perhaps even people from tropical locations.

They foresee dramatic population declines in Mexico, Central America, Africa, India, and other tropical locales if ecosystems or humans move due to climate change.

lizard on a leaf
(Credit: Carole Dupre/Flickr)

“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,” says Adam Sobel, professor of applied physics and math at Columbia University.

Because the tropics are uniformly hot, when things get hotter by just a small amount, populations will have to move far away to find relief.

“Imagine you have a fixed budget you can spend on your apartment and rents are the same throughout your entire neighborhood,” says Solomon Hsiang, chancellor associate professor of public policy at the University of California, Berkeley. “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.”

“As the tropics get hotter, you’ll have to go far…to cool off.”

The researchers 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.

Some oceanic and continental populations would have to move as far as 1,000 miles or more to stay within their “temperature budget,” the researchers say. Where do those populations end up? Simulations suggest the cooler edges of the tropics could get crowded, where populations might theoretically climb by 300 percent or higher. At those densities, disease and conflict over resources, among other issues, would bring their own complications.

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“We know that people and species of all kinds move for all kinds of reasons, not just to stay at the same temperature,” Sobel says. “At the same time, the uniformity of tropical temperatures is a basic fact about the temperature structure of Earth, and still will be as the climate changes. It seems like a very basic constraint that ought to be understood as we think about populations.”

“Another real problem arises when populations can’t move, but instead have to stay put and suffer the consequences of a new climate,” Hsiang says. “This can happen when human migrants run into political borders or when species physically can’t move fast enough.” The recent catastrophic bleaching of the Great Barrier Reef is an example of the latter.

To arrive at the findings, published in the journal Scientific Reports, the researchers compared today’s temperatures with climate model projections where Earth’s average temperature rose by 2 degrees Celsius this century. Even under these modest climate changes, considered “optimistic” compared to business-as-usual forecasts, population movements could be dramatic.  The tropics are unique in this extreme response to limited warming.

The authors are cautious in applying their findings to human populations, since moving is only one of many strategies humans use to cope with warming. Nonetheless, extraordinary human migrations cannot be ruled out, as the American Dust Bowl proved, they say.

Source: UC Berkeley