But that, say scientists at the University of Wisconsin-Madison, is killing us, too.It may be more subtle than a heat wave, but the toll air-conditioning takes could have a much deeper, long-term impact.In a study published in PLOS Medicine this week, the researchers suggest our AC dependency could kill as many as 1,000 more people every year in the eastern U.S. alone. The trouble, they note, is the burden air-conditioning puts on fossil-fuel burning electricity plants.