Brace yourself for coming heatwaves, there are at least 27 ways they can kill you

November 9, 2017, University of Hawaii at Manoa
Credit: C. Mora

A new systematic synthesis by researchers at the University of Hawaii at Manoa shows that there are at least 27 different physiological pathways in which a heatwave can kill a human being, and everyone is at risk.

Around the world, numerous cases have revealed the considerable dangers of extreme heatwaves. Over 70,000 people perished to the of the 2003 European , >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.

"We know of many case examples when people have died as a result of heatwaves," says Camilo Mora at the University of Hawaii at Manoa and lead author of the study. "However, why people died is a question whose answer is scattered."

In this paper, the researchers carried out a systematic review of medical literature into the known ways in which heat kills people. They identified five physiological mechanisms with impacts on seven . Then, they carried out secondary searches using as keywords all possible combinations of mechanisms and vital organs to ensure a systematic search of the literature. Out of 35 possible interactions (i.e., five mechanisms times seven vital organs), the authors found medical evidence for 27 of such interactions (see Table). Basically, there are at least 27 ways in which things can go wrong during a heatwave.

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.

Credit: C. Mora

While ischemia and heat cytotoxity can be lethal by themselves, the set of physiological responses to those two attacks pose an even greater risk of death. For instance, breaking of the intestine lining due to the chemical assault from ischemia and the thermal attack from heat cytotoxity, leads to the release of the gut content into the blood stream, which causes a third mechanism referred as "Systemic inflammatory response." In this, the body triggers an inflammation that facilitates access of white blood cells to fight the infection. However, the same inflammation that allows for can also facilitate further leakage of the guts and other organs whose membranes have been broken.

During all the internal mess created by ischemia, heat cytotoxity and the systemic inflammatory response, proteins that control blood clogging become overactive causing clots that can cut off supply to the brain, kidneys, liver and lungs; a mechanism called Disseminated Intravascular Coagulation. In turn, depletion of clotting proteins can lead to potentially fatal hemorrhaging even without injury. The final occurs when ischemia and heat cytotoxity, compounded by extraneous activity (e.g., going on a hike, exercising, working outdoors, farming, etc.), cause the breaking of skeletal muscle cells resulting in the leakage of myoglobin, which is toxic to the kidneys, liver and lungs.

"Dying during a heatwave is like a terror movie with 27 bad endings to choose from," says Mora. "It is remarkable that humanity overall is taking such a complacency on the threats that ongoing climate change is posing."

The paper further suggest that all heat damaging mechanisms can be triggered any time heat conditions are experienced, suggesting that anyone is at risk, with much greater risk for people with physical deficiencies or who cannot afford lifesaving tools, like AC.

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 , 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.

"Clearly, reducing the dangers of a warming world will require us to outperform even our most optimistic projections of climate change mitigation yet," the authors conclude.

Explore further: Be alert to the deadly danger of heatwaves

More information: Circulation: Cardiovascular Quality and Outcomes (2017). DOI: 10.1161/CIRCOUTCOMES.117.004233

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12 comments

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aksdad
1.7 / 5 (6) Nov 09, 2017
reducing the dangers of a warming world will require us to outperform even our most optimistic projections of climate change mitigation yet

Buy air conditioners for people who don't have them, which is immensely more practical, inexpensive and reasonable than any "climate mitigation" ideas the economics-challenged climate alarmists insist will save us all. Even a billion single room air conditioners would be vastly cheaper than their proposals.

there has been >2300% increase in the loss of human life from heatwaves as a result of less than ?1°C warming

Sure there has. One immediately suspects torturing of data.
daqddyo
4.5 / 5 (4) Nov 09, 2017
askdad:
And how much heat will these billion air conditioners pump into the atmosphere due to all the electricity they use (not to mention the heat released from electricity production?)
MR166
1.6 / 5 (7) Nov 09, 2017
Subject the same group to a harsh winter without fuel and see how many die. Many more will survive a heat wave than a harsh winter. This is just more propaganda paid for by the helpless taxpayer. These so called scientists are wasting our money, good money that should be used to solve real social problems.
MR166
1.7 / 5 (6) Nov 09, 2017
The saddest part of academia today is the intellectual capital and money wasted on this hoax. The world has real problems that must be solved and they are researching the equivalent of the sex lives of unicorns. They should stop working for the One World Government consortium and start working for the people who pay them.
dirk_bruere
3 / 5 (1) Nov 09, 2017
Connect the aircon to solar to be fully neutral (and cheap). Don't skimp on building insulation
tekram
4 / 5 (4) Nov 09, 2017
Many more will survive a heat wave than a harsh winter. ....

Why not cite one study to back up your assertion? A cursory survey of the published literature showed that heat wave deaths outnumber cold deaths at about 3 to 1. The heat wave in Russia in June 2010 led to 55,736 deaths. There has been no significant deaths from a cold wave in 50 years.

http://journals.a...86-7-937
MR166
1.8 / 5 (5) Nov 09, 2017
"The heat wave in Russia in June 2010 led to 55,736 deaths. "

So none of those people died of their chronic pre-existing conditions eh. That is one of the problems with studies like this, the same person dies multiple times from different causes.
MR166
1.8 / 5 (5) Nov 09, 2017
BTW don't forget to include all of plagues and massive crop failures that happen during the various cold periods.
MR166
2.3 / 5 (3) Nov 09, 2017
In theory it is possible for the same person to die from smoking, 2nd hand smoke, alcoholism, air pollution, animal fats, water pollution, cancer, heart disease, poverty, prejudice and heat prostration. It just depends on who is doing the survey. Add them all up an it subtracts about 110 years from the average life span.
Mark Thomas
5 / 5 (3) Nov 09, 2017
"Buy air conditioners for people who don't have them"

You would have us do anything to keep burning oil. Keep that Koch Brothers' crap to yourself. The answer may be as simple as wind power, solar power, electric vehicles and LED lighting. No surprise that oil barons like the Koch Brothers don't like that answer, because it will cost them billions.

"intellectual capital and money wasted on this hoax"

Hey troll, any real debate about global warming is long over. All the world's nations, except for the United States of Trumpia, agree global warming is real and something needs to be done. You are persuading nobody here. Note that most Americans agree with the rest of the world, but the Republican Party is the bought-and-paid-for lackey of the mighty oil and coal industries.
Mark Thomas
4 / 5 (4) Nov 09, 2017
As global warming continues to unfold, we Americans should always remember that it was the Republican Party that lied to us about global warming for decades and they did everything they could to let it happen. All for the money.
alkane
1 / 5 (1) Nov 11, 2017
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.

Utter nonsense, This was always the outcome, makes one wonder why they even bothered with the 'research' in the first place.

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