The U.K. is enduring a serious heat wave that has resulted in an estimated 540 to 760 deaths over nine days. Yet the highest the temperature has risen is 90 degrees Fahrenheit. Most of the time, temperatures have hovered in the high 80s, which, while toasty, doesn't seem like it could kill hundreds of people.
One reason for this is that air-conditioning is relatively rare in England. Only 0.5 percent of homes in the U.K. have air-conditioning, according to the BBC. Compare that to the United States, where an estimated 87 percent of households have an air-conditioning unit.