Dangerous high-humidity heat emerging across the globe

Dangerous high-humidity heat emerging across the globe. Scientists recently predicted that a dangerous mix of heat and humidity will strike tropical regions by the end of this century, creating conditions that may be intolerable for humans.

But now, researchers at the Earth Institute have discovered that potentially deadly extremes of high-humidity heat have already arrived in places all over the world. 

The experts have pinpointed thousands of examples where rare or unprecedented levels of heat and humidity occurred in Asia, Africa, Australia, South America, and North America. 

“These measurements imply that some areas of Earth are much closer than expected to attaining sustained intolerable heat. It was previously believed we had a much larger margin of safety,” said Steven Sherwood, a climatologist at the University of New South Wales.

Along the Persian Gulf, the researchers identified more than a dozen brief outbreaks that surpassed the theoretical human survivability limit. 

So far, the bouts of extreme heat and humidity have been confined to local areas and lasted only a few hours. However, the researchers found that the events are increasing in frequency and intensity.

“Previous studies projected that this would happen several decades from now, but this shows it’s happening right now,” said study lead author Colin Raymond. “The times these events last will increase, and the areas they affect will grow in direct correlation with global warming.”

Based on weather data from 1979 to 2017, the researchers determined that extreme heat and humidity events doubled over the study period. 

The areas with repeated incidents include India, Bangladesh, Pakistan northwestern Australia, and along the coasts of the Red Sea and Mexico’s Gulf of California. Parts of southeast Asia, southern China, subtropical Africa, and the Caribbean were also hit with high-humidity heat.

The southeastern United States experienced these conditions dozens of times, primarily along the Gulf Coast in east Texas, Louisiana, Mississippi, Alabama, and the Florida Panhandle, with Buloxi and New Orleans being hit the hardest. The high-humidity heat was also identified in Arkansas and along the southeastern coastal plain.

The humid heat waves are most common on the coastlines of confined seas, gulfs, and straits, where evaporating ocean water provides abundant moisture to be sucked up by hot air. Further inland, monsoon winds or wide areas of crop irrigation appear to make the same type of contribution to humidity.

Heat-related illnesses already kill more U.S. residents than any other natural hazard, including hurricanes or floods. 

Last year, the website InsideClimate News reported that cases of heat stroke or heat exhaustion among U.S. troops on domestic bases increased by 60 percent from 2008 to 2018. Most of the soldiers that died were located in the Southeast. In Russia and Europe, where far fewer people have air conditioning, high-humidity heat waves have killed tens of thousands.

“We may be closer to a real tipping point on this than we think,” said study co-author Radley Horton.

Many people in the poor countries that are most at risk do not have electricity or air conditioning. Furthermore, many of these people rely on subsistence farming that requires heavy labor outdoors. According to Horton, these facts could make some of the most affected areas basically uninhabitable.

Kristina Dahl, a climatologist at the Union of Concerned Scientists, said the new study shows “how close communities around the world are to the limits.” She added that some places may already be seeing conditions worse than the study suggests, because weather stations do not necessarily pick up hot spots in dense city neighborhoods built with heat-trapping concrete and pavement.

The study is published in the journal Science Advances.

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By Chrissy Sexton, Earth.com Staff Writer