USA: Increasing humidity, driven in part by climate change, is making even modest heat waves unbearable

By Matthew Cappucci

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It’s all about the heat index

Heat waves in Europe are seldom accompanied by the humidity we get in the United States. Our proximity to the Gulf of Mexico and the Atlantic Ocean opens the doors to sauna-like moisture streaming northward unimpeded, bringing the sultry mugginess over wide swaths of the Deep South and Southern Plains this time of year, along with the East Coast on occasion.

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The heat index is essentially a “feels like” temperature that takes temperature and humidity into account. Heat places more strain on your body if it is accompanied by high humidity, since it inhibits the body’s ability to perspire and cool down. Beads of sweat evaporate from our skin and extract thermal energy, taking heat out of our body and making us feel cooler.

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“By the mid-21st century (2036—2065) … the annual numbers of days with heat indices exceeding 105 degrees are projected to triple,” said [a study by the Union of Concerned Scientists], which focused specifically on heat indexes rather than actual air temperatures.

The group also estimated that, during the same time frame, a quarter of the United States would venture into “no analog” territory every year. In other words, 25 percent of the United States will be venturing into unprecedented heat-index territory regularly.

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