WVK Wrote:
-------------------------------------------------------
> "The Mexican police will round up illegal American
> migrants surging into Mexico seeking work as field
> hands.” — “Dead Heat: The Race Against the
> Greenhouse Effect,” Michael Oppenheimer and Robert
> H. Boyle, 1990."

The must have had the map upside down in 1990, in 2010:

Using state-level data from Mexico, we find a significant effect of climate-driven changes in crop yields on the rate of emigration to the United States. The estimated semielasticity of emigration with respect to crop yields is approximately −0.2, i.e., a 10% reduction in crop yields would lead an additional 2% of the population to emigrate. We then use the estimated semielasticity to explore the potential magnitude of future emigration. Depending on the warming scenarios used and adaptation levels assumed, with other factors held constant, by approximately the year 2080, climate change is estimated to induce 1.4 to 6.7 million adult Mexicans (or 2% to 10% of the current population aged 15–65 y) to emigrate as a result of declines in agricultural productivity alone.
[www.pnas.org]