Brace Yourself for Coming Heatwaves, There Are At Least 27 Ways They Can Kill You

Around the world, numerous cases have revealed the considerable dangers of extreme heatwaves.  Over 70,000 people perished to the extreme heat of the 2003 European heatwave, >10,000 people to the 2010 Russian heatwave, over 2,000 to the 2015 India heatwave, and altogether, over 800 cases of deadly heatwaves have been documented worldwide since 1980.  At times, the impacts of deadly heat are not measured in human lives, but in the numbers of people imprisoned indoors.  In the last two years, for instance, millions of Americans have been told to stay indoors in cool places to avoid dangerous heat outdoors.  Unfortunately, according to recent studies these deadly heatwaves are projected to worsen even with aggressive mitigation of greenhouse gases.  Yet, the significance of this deadly heat will depend on the sensitivity of the human body to heat, and a new synthesis paper shows that we are more sensitive to heat than you may think.  The paper appears in the American Heart Association journal Circulation: Cardiovascular Quality and Outcomes.
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Briefly, when the body is exposed to extreme heat, the hypothalamus generates a reaction in which it redirects blood flow to the skin, with the purpose of cooling down.  This compensatory shunting of blood to the skin results in inadequate blood flow to other organs (a mechanism called Ischemia), where it creates anoxic conditions and damaging chemical compounds.  In turn, if body temperature surpasses the optimal body temperature (because it is too hot), this will damage cells directly in a mechanism referred as heat cytotoxity.  Both ischemia and heat cytotoxity are deadly conditions that can impact the functioning of the brain, heart, kidneys, liver, and perhaps more critically your guts.
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In the paper, the authors comment that in the last decade, there has been >2300% increase in the loss of human life from heatwaves as a result of less than 1°C warming.  With 27 ways to die from extreme heat, the death toll that occurred with <1°C of warming emphasizes the heightened risk to human life even under the optimistic target of allowing the planet to warm up by another 1°C.

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