You can get anything you like out of a climate model. It is just a patchwork of guesses and leaves out lots of influential factors. Just alter one assumption (e.g. the effect of clouds) and the answers can change dramatically

According a new computer model, a total of nearly seven million additional Mexicans could emigrate to the U.S. by 2080 as a result of reduced crop yields brought about by a hotter, drier climate—assuming other factors influencing immigration remain unchanged.

“The model shows that climate-driven refugees could be a big deal in the future,” said study co-author Michael Oppenheimer, an atmospheric scientist at Princeton University in New Jersey.

Using data on Mexican emigration as well as climate and crop yields in 30 Mexican states between 1995 and 2005, Oppenheimer and colleagues created the computer model to predict the effect of climate change on the rate of people crossing the border.

In that ten-year period, 2 percent of the Mexican population emigrated to the U.S. for every 10 percent reduction in crop yield.

Using the model to extrapolate this real-world figure over the next 70 years, the researchers calculated that 1.4 to 6.7 million adult Mexicans—a number roughly equal to 10 percent of Mexico’s current adult population—could migrate to the U.S. by 2080.

The research is one of the first attempts by scientists to put hard numbers on how climate change can affect human migration patterns.

“Our study is the first to build a model that can be used for projecting the effects on migration of future climate change,” Oppenheimer said.

Global Warming Study “a Simplification”

Though the new global warming study is “original and very interesting,” it shouldn’t be interpreted as a forecast of what will happen, economist Ian Goldin, who wasn’t involved in the project, said via email.

“The [end of the] time range—2080—is a very long time off, and there are many other factors [besides climate change] which may lead to a very different outcome,” said Goldin, director of the University of Oxford’s James Martin 21st Century School.

Barry Smit, a climate-impact scientist at the University of Guelph in Canada, agreed.

“I wouldn’t take these numbers to the bank,” said Smit, who also wasn’t involved in the research, which is published in this week’s issue of the journal Proceedings of the National Academy of Sciences.

To reach their conclusions, the authors had to make some “heroic assumptions,” Smit said, such as that the current economic and political situations of the U.S. and Mexico won’t change for decades.

Study co-author Oppenheimer acknowledged there are many uncertainties in his team’s model. But it’s important for scientists to investigate climate change-induced migration quantitatively, he said.

“This is the first time anybody’s built a model to do this,” Oppenheimer said. “It’s a simplification, and there are a lot of assumptions, but it’s the start of a learning process. As we learn more, the model will improve, and the numbers will get more reliable.”