Heat stress kills more people worldwide than any other weather phenomenon, including cyclones and floods. 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 diarrhoea.
Deaths rise by over 50 percent on average during heat waves, and are expected to climb even higher over the coming decades as a result of global warming.
An analysis of ten Canadian cities found that heat-related mortality could increase in several large cities if temperatures increase as predicted by the greenhouse effect. Affected cities would be those that come under the influence of hot humid air masses -- Toronto, Montreal and Ottawa -- and in Montreal mortality rates could be twenty times that of today.