Climate Change Is Already Causing Mass Human Migration

When temperatures are high, Pakistani men are 11 times more likely to move out of town

01_29_2014_pakistani farmer.jpg
A. Yaqub / CIMMYT

There are a lot of reasons people move: for work, for love, for the draw of the big city or the quiet of nature. But as the world continues to warm, it's expected that global climate change will become another factor driving people to move: to dodge coastal erosion and sea level rise, to follow changes in rainfall, to avoid strengthening storms. Climate change is already inducing marine animals to migrate, and according to a new study published in the journal Nature Climate Change, it's starting to make people move, too.

For the past 21 years, researchers have been studying the migration patterns of people in Pakistan. (Similar studies are done in America—that's how we know that most emigrants from New York are going to Florida.) Migration data in hand, the scientists, led by the International Food Policy Research Institute's Valerie Mueller, measured the relationship between Pakistanis' movements and changes in a handful of environmental variables, from the quantity and timing of rainfall, to temperature, the strength of the annual monsoon and the occurrence of floods.

“This approach reveals a complex migratory response that is not fully consistent with common narratives of climate-induced migration,” the scientists wrote in their report

Traditionally, scientists have assumed that it is big, catastrophic natural disasters that drive people to pack up and leave. But as with those who hunker down in Tornado Alley, the researchers found that even though Pakistan is prone to extreme floods, like the devastating 2010 floods that affected 20 million people and forced 14 million to move temporarily, flooding in general has little effect on where people chose to live long-term.

Instead, they found, high temperatures, particularly during the spring and winter farming season, were the dominant driver of mass migration. It's not that it suddenly became too hot for people to live. But as temperature and weather patterns change, previously productive ground may become uneconomical to work. High heat wipes out the farming economy, the researchers suggest, causing Pakistani men to pack up and leave for greener pastures.

“Thus, we are left with an overall picture that heat stress—not high rainfall, flooding, or moisture—is most strongly associated with migration. The risk of a male, non-migrant moving out of the village is 11 times more likely when exposed to temperature values in the fourth quartile,” they wrote.

The failure of the farm and the exodus that follows, the scientists say, sends a rippling shock through the rest of the economy as people stop buying and start leaving.

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