Deaths rise by over 50 per cent on average during heat waves, and are expected to climb even higher over the coming decades as a result of global warming. People can die from heat stress when severe dehydration causes the body to release heat shock proteins. These trigger a cascade of biochemical events that can culminate in a heart attack or stroke.
Heat stress can also cause exhaustion, fainting, vomiting and diarrhea.
Most existing national heat warning systems rely on a set of arbitrary criteria. It's not just heat. Dangerous conditions stem from a wide range of factors, he says, such as height above sea level and building design. According to Kalkstein, the cities hardest hit by heat stress are not the hottest. Instead, very variable summer weather in certain cities, such as Melbourne and New York, causes the greatest loss of life, mainly because some people cannot physically adjust to the changes quickly enough.