The study began by examining two databases: asylum applications to the EU between 2000 and 2014, and average temperatures across 103 countries.

The authors omitted asylum data from 2015 and 2016, when refugees were fleeing the Syrian Civil War and other conflicts. More than 1 million people applied for asylum annually during those two years, a spike well above the average 350,000 annual applicants from 2000 to 2014.

Schlenker and Missirian found an early correlation between weather and migration, but they waded through the data, trying to account for as much statistical noise as possible. They removed one-year shocks from events like the onset of the global financial crisis. They also factored in the difference between hot and cold countries, as a naturally colder country might be able to deal with a few extra degrees more easily than a hot country.

Ultimately, they found that the entire effect in asylum increases was attributable to temperature shocks in maize-growing countries that hit during the growing season, in the area where crops are grown.

Though the research seems to examine the relationship between climate change and migration, it’s actually getting at the deeper question of climate and governmental collapse or oppression. That’s because of the definition of forced migration: Only refugees from conflict or persecution can apply for permanent asylum in another country. The 1951 UN Refugee Convention, which every nation in the EU has signed, does not define a refugee as someone fleeing a country for economic reasons.

If a country suffered a temperature shock, then its refugees were three times more likely to be accepted for asylum than the average applicant to the EU. To Schlenker, this points to a deep connection between climatic crises and military conflict or persecution.

“The mechanism through which this works is conflict,” he told me. “We don’t know why they get accepted or not, but people in destination countries in the EU find them to be worthy of protection.”

The paper also projected its findings forward, by examining when various climate models believe weather shocks in growing regions could become more likely. They found modest increases. In a world that gets carbon-dioxide pollution under control and holds global warming to roughly 2 degrees Celsius, the number of asylum applications to the EU could rise by about 28 percent.

But if carbon pollution continues unabated, and global temperatures rise by about 5 degrees Celsius, annual applications could rise by 188 percent by 2070. More than 650,000 people could seek protection in the European Union annually.

Schlenker made it clear that these numbers should be used as tools for thinking and not final projections. “This is the best estimate we can do with current data, but there’s lots of asterisks,” he said. The projections could err too high, because they don’t account for global adaptation to warmer weather. But they could also still be too low, because they can’t anticipate political tipping points like civil wars or regime change.