Associated Press: Global warming is uprooting people from their homes and, left unchecked, could lead to the greatest human migration in history, said a report released Wednesday. Estimates vary on how many people are on the move because of climate change, but the report cites predictions from the International Organization for Migration that 200 million people will be displaced by environmental pressures by 2050. Some estimates go as high as 700 million, said the report, released at U.N negotiations …