Humidity may prove breaking point for some areas as temperatures rise

It will also be dangerous to plants and animals.

https://www.eurekalert.org/pub_releases/2017-12/teia-hmp122017.php

Public Release: 22-Dec-2017
Humidity may prove breaking point for some areas as temperatures rise, says study
From US south to China, heat stress could exceed human endurance
The Earth Institute at Columbia University

Climate scientists say that killer heat waves will become increasingly prevalent in many regions as climate warms. However, most projections leave out a major factor that could worsen things: humidity, which can greatly magnify the effects of heat alone. Now, a new global study projects that in coming decades the effects of high humidity in many areas will dramatically increase. At times, they may surpass humans' ability to work or, in some cases, even survive. Health and economies would suffer, especially in regions where people work outside and have little access to air conditioning. Potentially affected regions include large swaths of the already muggy southeastern United States, the Amazon, western and central Africa, southern areas of the Mideast and Arabian peninsula, northern India and eastern China.

"The conditions we're talking about basically never occur now--people in most places have never experienced them," said lead author Ethan Coffel, a graduate student at Columbia University's Lamont-Doherty Earth Observatory. "But they're projected to occur close to the end of the century." The study will appears this week in the journal Environmental Research Letters.

Warming climate is projected to make many now-dry areas dryer, in part by changing precipitation patterns. But by the same token, as global temperatures rise, the atmosphere can hold more water vapor. That means chronically humid areas located along coasts or otherwise hooked into humid-weather patterns may only get more so. And, as many people know, muggy heat is more oppressive than the "dry" kind. That is because humans and other mammals cool their bodies by sweating; sweat evaporates off the skin into the air, taking the excess heat with it. It works nicely in the desert. But when the air is already crowded with moisture--think muggiest days of summer in the city--evaporation off the skin slows down, and eventually becomes impossible. When this cooling process halts, one's core body temperature rises beyond the narrow tolerable range. Absent air conditioning, organs strain and then start to fail. The results are lethargy, sickness and, in the worst conditions, death.

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"It's not just about the heat, or the number of people. It's about how many people are poor, how many are old, who has to go outside to work, who has air conditioning," said study coauthor Alex deSherbinin of Columbia's Center for International Earth Science Information Network. De Sherbinin said that even if the weather does not kill people outright or stop all activity, the necessity of working on farms or in other outdoor pursuits in such conditions can bring chronic kidney problems and other damaging health effects. "Obviously, the tropics will suffer the greatest," he said. Questions of how human infrastructure or natural ecosystems might be affected are almost completely unexplored, he said.

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