Heat stress may affect 1.2 billion people by 2100

Heat stress from extreme heat and humidity will annually affect areas now home to 1.2 billion people by 2100, according to a study by Rutgers. The figures are based on current greenhouse gas emissions.  

More than four times the number of people affected today by heat stress will be affected by 2100. This is more than 12 times the number who would have been affected without industrial era global warming.

Rising global temperatures are increasing exposure to heat stress, which harms human health, agriculture, the economy and the environment, according to a Rutgers statement. Most climate studies on projected heat stress have focused on heat extremes but not considered the role of humidity, another key driver.

“When we look at the risks of a warmer planet, we need to pay particular attention to combined extremes of heat and humidity, which are especially dangerous to human health,” said senior author Robert E. Kopp.

Heat stress is caused by the body’s inability to cool down properly through sweating. Body temperature can rise rapidly, and high temperatures may damage the brain and other vital organs.

The study looked at how combined extremes of heat and humidity increase on a warming Earth, using 40 climate simulations to get statistics on rare events. The study focused on a measure of heat stress that accounts for temperature, humidity and other environmental factors, including wind speed, sun angle and solar and infrared radiation.

Annual exposure to extreme heat and humidity in excess of safety guidelines are projected to affect areas currently home to about 500 million people if the planet warms by 1.5 degrees Celsius and nearly 800 million at 2 degrees Celsius. An estimated 1.2 billion people would be affected with 3 degrees Celsius of warming, as expected by the end of this century under current global policies.

Image credit: Raïssa, flickr/Creative Commons

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