A new scientific study published Thursday reawakened a fraught debate over one of the more contested, and potentially devastating, consequences of a warming climate: changing patterns of human migration.
The work, by two researchers at Columbia University, examined potential links between swings in temperature in 103 countries and the volume of asylum applications to the European Union over the 15-year period between 2000 and 2014. The authors then tried to determine the likely rise in asylum applications as the Earth grows warmer between now and 2100.
Their analysis? That the E.U. could see an increase of 28 percent of applications under “moderate” global warming condition, and as much as a 188 percent spike — or 660,000 more applications annually — under more severe warming.
“Two hundred, 300 years ago, there were mass crop failures in Europe, and that led to huge migration decisions,” said Wolfram Schlenker, the Columbia economist who authored the study with doctoral student Anouch Missirian. “But I was surprised that even in today’s environment, we find this significant and robust relationship.”
The work, published in the journal Science, follows still-contested research from 2015 that focused on the potential role of climate change in the crisis in Syria. It contended that a drought between 2007 and 2010 in the Fertile Crescent region helped impel the political dissolution that followed, and that the drought itself had been made more likely to occur because of a warming climate.
In the new study, whose data does not include the period in which Europe saw a truly dramatic spike in migration beginning in 2015, Missirian and Schlenker do not assert that human-caused climate change is driving current migration patterns. Instead, it simply finds asylum applications swing as temperatures deviate from a climatic optimum of around 68 degrees Fahrenheit.
“We look at in each country, if you’re hotter than normal or colder than normal, does it increase your applications?” Schlenker said.
The research found that weather fluctuations accounted for only a small part of the roughly 352,000 asylum applications on average each year for the period between 2000 through 2014 — but that a statistical relationship did exist. Specifically, the study examined temperatures fluctuatioins suggesting a possible link between reduced agricultural productivity and the desire to migrate to another country.
The authors then take the more striking — and potentially controversial — step of projecting the number of future asylum applications in the E.U. based on the expected rise in temperatures caused by climate change. Schlenker acknowledged that the effort involves considerable uncertainty. “There are obviously many other factors beyond weather that impact asylum applications,” he said.
Academics and experts consulted by The Washington Post had divided reactions to the work.
Marshall Burke, a Stanford researcher who has published work on the relationship between warming temperatures and increased risks of conflict between and within nations, called the study “an excellent paper on a very important, much hypothesized and still poorly understood topic.”
“The potential link between climate and migration has been talked about a lot, but there haven’t been any studies that have been able to make a clear link at a broad scale, and at the same time understand what the potential mechanism is — and this paper does both, which is a huge contribution,” he said in an email.
Mike Hulme, a professor of human geography at the University of Cambridge, said he found several flaws in the study, including the inherent uncertainty of trying to predict relatively precise numbers of future asylum seekers based merely on projections of an increase in global temperatures.
“They are making a claim 83 years into the future … I just don’t believe the plausibility of those numbers. The world changes,” Hulme said. “It’s a put-your-finger-in-the-wind kind of number.”
Hulme also said the study “oversimplifies” the problem of mass migrations by focusing on climate as a primary driver.
“I’d want to find out what is the most decisive factor that shapes asylum-seeking behaviors, not can I prove that temperature is a factor? It’s a different question,” he said. “Trying to reduce the complexity of migration, refugee and asylum-seeking behaviors … to simply a temperature predictor isn’t anywhere close to faithful representation of reality.”
Michael Werz, a senior fellow at the Center for American Progress who has studied the intersection between climate change and societal upheaval, had reservations about the study’s conclusions, though he called the study “one important piece of the puzzle, but it’s not the only one.”
He said it is difficult enough to determine a causal relationship between global warming and migratory movements, and even more fraught to try to predict specific numbers of asylum seekers in the future. The study notes that formal asylum seekers are only 10 percent of the total number of people who migrated during the study period in question.
“The motivation is complex, and so is the science,” Werz said. Though he added that evidence continues to grow that changing climates will force certain populations to seek refuge elsewhere.
“There is a mass of evidence that climate is impacting the way that people behave. Also substantial evidence that climate is a likely driver or contributor to massive migratory movements. It’s hard to argue it’s the only driver, but it is certainly a driver.”