WASHINGTON — Poor and southern U.S. counties will get hit hardest by global warming, according to a first-of-its-kind detailed projection of potential climate change effects at the local level.The study, published Thursday in the journal Science , calculates probable economic harms and benefits for the more than 3,100 counties in the United States under different possible scenarios for worldwide emissions of heat-trapping gases. It looks at agriculture, energy costs, labor costs, coastal damage from rising seas, crime and deaths, then estimates the effect on average local income by the end of the century.Researchers computed the possible effects of 15 types of impacts for each county across 29,000 simulations."The south gets hammered and the north can actually benefit," said study lead author Solomon Hsiang, a University of California economist. "The south gets hammered primarily because it's super-hot already.