Read more: 鈥�Climate change: It鈥檚 even worse than we thought鈥�
In August 2003, Europe was hit by an extraordinary heatwave. In parts of France, the temperature hit 40 掳C for seven days in a row. So many people died that a refrigerated warehouse near Paris was co-opted to store bodies. A study in 2008 concluded that . Most of the victims were elderly or ill, but not all.
Heat has more subtle effects, too. The . If it gets too hot, people begin to suffer from exhaustion, heatstroke and kidney failure.
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Recent studies suggest the effects of climate change on human health and economic output have been underestimated. 鈥淚 suspect heat stress will prove the single worst aspect of climate change,鈥� says , an atmospheric scientist at the University of New South Wales in Sydney, Australia.
What matters is not so much the air temperature but the temperature of our skin: sweating cools our skin, but is less effective in humid conditions. The combined effect of heat and humidity can be gauged by the wet-bulb temperature of a 鈥渟weating鈥� thermometer 鈥� a thermometer wrapped in a damp cloth.
Currently, the maximum wet-bulb temperatures reached anywhere on the planet do not exceed 31 掳C, but we do not expect that to remain so. 鈥淎ll our models show a , and as a result higher heat stress and health impact,鈥� says at the Institute for Atmospheric and Climate Science in Zurich, Switzerland.
It is very difficult to put precise numbers on the effects, because if we are healthy we don鈥檛 just sit there sweating when it gets hot. We seek out cool spots, or install air conditioning, and so on. Killer heat in one country is no problem in another where people and infrastructure are adapted to it.
But there is an absolute limit. We cannot survive wet-bulb temperatures of 35 掳C or more for long, even standing naked in front of a fan. And concluded that if the world warms by 7 掳C, parts of the world will start to exceed this limit occasionally. Eventually, vast swathes of Africa, Australia, China, Brazil, India and the US will become uninhabitable for at least part of the year.
Something similar may have happened before 鈥� a mass extinction 250 million years ago is now blamed on temperatures rising too high for most animals to survive. 鈥淚t looks like if we fully 鈥榙evelop鈥� all of the world鈥檚 coal, tar sands, shales and other fossil fuels we run a high risk of ending up in a few generations with a largely unlivable planet,鈥� says Sherwood.
