BONN, Germany — 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 for a new climate treaty. Researchers questioned more than 2,000 migrants in 23 countries about why they moved, said Koko Warner of the U.N. University, which conducted the study with CARE International and the Center for International Earth Science Information Network at Columbia University. The results were ‘a clear signal’ that environmental stress already is causing population shifts, she said, and it could be ‘a mega-trend of the future.’ The potential for masses of humanity fleeing disaster zones or gradually being driven out by increasingly harsh conditions is likely to be part of a global warming agreement under negotiation among 192 countries. A draft text calls on nations to prepare plans to adapt to climate […]