Seven million Mexicans could be forced to move to the United States over a period of 70 years. That is the conclusion of a study that was recently published in Proceedings of the National Academy of Sciences. The researchers have based the numbers in the study on migration numbers, and the changes in climate and crops, in the time period between 1995 and 2005. The study suggests that for every 10 percent crops decreases in Mexico, another two percent of the Mexican population would move to the United States. The U.S. National research Council has estimated that crop yields of corn would drop between 5 to 15 percent in North America, for each degree Celsius warmer the average global temperature gets. According to the new study the number of people that would have to flee the warming climate could be anywhere between 1.4 million to 6.7 million. The numbers depend on how much global warming that will actually occur, and whether other factors remain equal. However, other researchers, who are not part of the recent study, say immigration patterns are complex, and that they do not only depend on crop sizes or material wealth. One researcher points out that for most poor people in Mexico emigrating to another country would hardly be an option, but many would instead move from the country side to the cites. The majority of Mexicans who depend on corn to survive would not have enough money to risk emigrating to the U.S.