By 2100, climate change could mire half the world's population in a food crisis, according to a new report. The analysis is based on data from 23 climate change models gathered in the 2007 report by the Intergovernmental Panel on Climate Change. It predicts a 6 degree Fahrenheit rise in average growing-season temperatures in many areas and a 20 to 40 percent drop in crop yields. The hardest hit will be the tropics and subtropics, home to some of the world's poorest populations.