Some will say this study is just a wild assumption – that you can’t untangle ‘normal’ droughts from impacts of climate change. First remember climate change is a force multiplier: it makes droughts and floods far worse than normal. And secondly it is pretty obvious that if temps climb much higher in most parts of Mexico there will be major crop failures and then what are people supposed to do? Lay down and die? They are going to move — wouldn’t you? — Stephen
From Sci Am magazine:
A reduction in crop yields could spur even more migration from south to north, a new analysis finds
By David Biello
Climate change’s impacts on crop yields may force as many as seven million Mexicans to emigrate to the U.S. over the next 70 years, according to research published July 26 in the Proceedings of the National Academy of Sciences. The study is among the first to attempt to put hard numbers on questions about “environmental refugees” that may be caused by climate change.
“There is a significant response of emigration from Mexico to past climate variations,” says atmospheric scientist Michael Oppenheimer of Princeton University, an author of the study. “Climate changes predicted by the global circulation models would cause several percent of the Mexican population to move north [if] all other factors are held constant.”
via Climate Change May Mean More Mexican Immigration: Scientific American.
Stephen Leahy, International Environmental Journalist 
It is not only Latin America, but also southern India, Africa and other areas affected by both water shortages and excess heat– both of which can make farming extremely difficult.
I find in reading those sites that say that climate problems are a myth that their evidence is very sparse and inconclusive. Recently I read Book 1 of the free e-book series “In Search of Utopia” (http://andgulliverreturns.info), it blasts their lack of evidence relative to several myths. The book, actually the last half of the book, takes on the skeptics in global warming, overpopulation, lack of fresh water, lack of food, and other areas where people deny the evidence. I strongly suggest that anyone wanting to see the whole picture read the book, at least the last half. There is also up to date information at:http://www.newscientist.com/article/dn11462-climate-change-a-guide-for-the-perplexed.html
Millions are already affected around the world: from an article earlier this year: Climate change is not an abstract concept. It already results in the deaths of 300,000 people a year, virtually all in the world’s poorest countries. Some 325 million people are being seriously affected, with economic losses averaging 125 billion dollars a year, according to “The Anatomy of a Silent Crisis“, the first detailed look at climate change and the human impacts. http://bit.ly/9eqKod