UPDATED 7-28

Scientific American has posted a news and commentary piece on a study, just published in the Proceedings of the National Academy of Sciences, that links climate change to increased migration from Mexco to the US.  The author, David Biello, sent me an embargoed copy of the study a few days ago and asked for my comments – which he was kind enough to draw from at length in his article.
In a general way, I am very supportive of work that examines the connection between climate change/environmental change and migration – mostly because so little work has been done on the topic, and the assumptions about the connections between migration and environment that drive policy are so often wildly incorrect.  However, I am a bit leery of this study, as I feel like it is making a classic mistake in environment-migration studies: it is trying to identify the portion of the migration decision that is about environmental change.  As I have argued elsewhere, there is little point in trying to isolate environmental factors from all of the factors that contribute to migration.  Biello quoted me quite accurately:

“Migration decisions, like all livelihood decisions, are about much more than material quality of life,” argues geographer Edward Carr of the University of South Carolina, who studies human migration in countries such as Ghana and was not involved in the Mexico emigration research. “What I am seeing in sub-Saharan Africa are very complex patterns in which environmental change is but one of several causal factors.”

What I am worried about here is a sort of intellectual ambulance-chasing, where the research is driven by a sexy topic (the intersection of climate change and Latino migration, which is sure to bring out the crazies on all sides) regardless of whether or not the fundamental research question is all that sound.  The fact that several researchers quoted in the piece (myself included) were able to quickly poke significant holes in the study suggests that this publication falls into this problematic category.  First, the migration pattern examined and emphasized in this project is likely to be very, very small relative to other kinds of movement.

“Most often international migration is not an option and rural residents migrate to urban areas, contributing to urbanization and urban poverty in developing countries,” says sociologist Elizabeth Fussell of Washington State University.

That is certainly the case in Mexico, according to population and migration researcher Haydea Izazola of the Universidad Autónoma Metropolitana-Xochimilco, also not part of Oppenheimer’s team for the new study. “The great majority of the rural population who grow maize—rain-fed agriculture—for their own consumption are the poorest of the poor and lack the means to invest in the very expensive and risky migration venture.”

Further, the very models that predicted the impact of climate change on Mexican agriculture were not applied to the economy of the US, where the migrants are supposed to be headed.

Crop yields in the U.S. will likely suffer as well. “People do not move blindly; they move to greater opportunity,” Carr notes. “So we should probably be using [these economic and climate] models to examine the impact of future climate change on various migrant-employing sectors of the southwestern U.S. economy.”

While the research team that published this study intends to examine this issue, it calls into question even this preliminary study.  I’m honestly surprised this got through peer review . . . except, perhaps that it was too sexy to pass up.
UPDATE: I wrote this late last night, and so was a bit spacey – as a friend of mine reminded me, there is another huge problem with the study – a lot of the “Mexican” migration that people are talking about in the popular media, and indeed in this study, is in fact Latino migration from Central America more broadly.  As these areas were not modeled in this study, we have yet another gaping hole to address.  I repeat: how did this get though peer review?
UPDATE: Well, people are jumping all over this article.  Pielke’s site has a review with a similar take to my own . . .