Take this one:
"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." [Global Warming Means More Mexican Immigration? By Ker Than, National Geographic, July 26, 2010]
I'm not a global warming skeptic. Maybe something like this will happen. But the simple fact is that a great many Mexican agricultural workers—specifically, the ones most likely to be pushed north by global warming—are already here. They have already been displaced by a change in the economic climate: the North American Free Trade Agreement.
NAFTA hit the Mexican agricultural sector hard. As part of the 1994 trade pact Mexico had to eliminate all tariffs on agricultural imports. That inevitably meant the end for small Mexican farmers—especially corn farmers.
Before NAFTA nearly half of all Mexican land under cultivation was devoted to corn; Mexico was self-sufficient in its corn production. But ninety percent of the corn raised in pre-NAFTA Mexico was planted on low tech, labor intensive plots of land less than 11 acres; 40% on less than two acres. By comparison, a typical U.S. corn farm is about 270 acres, so highly mechanized and fertilized that only about one-half hour of labor is required to produce 1 metric ton of corn. [USDA Figures (PDF)]
Small Mexican farms simply could not withstand the post-NAFTA flood of U.S. imports, particularly when combined with the Mexican government's decision to dramatically scale down its support of small-scale farmers. The not-unintended consequence: Agricultural employment in Mexico fell from 8.1 million in the early 1990s to only 6 million in 2006 - a loss of more than 2 million agriculture-related jobs. [A Fair Farm Bill and Immigration, Institute for Agriculture and Trade Policy, 2007 (PDF)]
It's not that Mexican agriculture has disappeared. Indeed, Mexico exports more farm products today than prior to NAFTA. Thanks to capital investments from the U.S. and other countries, Mexican farms are larger, more efficient, and more profitable than before NAFTA. They could likely turn a profit even with global warming.
Another not unintended consequence: Many of the displaced Mexican farmers crossed the border to become illegal workers in U.S. corporate mega-farms. About three-quarters of the hired crop labor force in the U.S. was born in Mexico, and an estimated 53 percent of those laborers are undocumented. Farm workers earn an average of $8,000 per year, giving them the dubious title of having the lowest wages of any U.S. wage and salary worker. [The National Agricultural Workers Survey]
We say "not unintended" because this outcome is exactly what a long line of Presidents of the U.S. and Mexico (and their corporate supporters) envisioned when promoting free trade in the Americas. Free trade is a great leveler—workers in high income countries make less, workers in poor income make more. By contrast, owners of capital benefit no matter where they are located.
Free trade can be seen as the flip side of open borders immigration. They both serve the same special interests.
NAFTA was supposed to raise incomes of poor Mexicans and reduce illegal immigration. It accomplished the first objective: even at $8,000 per year Mexican farm workers are ahead of where they were pre NAFTA.
The problem is they are not in Mexico.