As heatwaves ramp up across the world, meteorologists and environmental advocates alike are worried about "wet-bulb temperatures,” measurements of heat and humidity that are particularly dangerous because they decrease the human ability to perspire and cool. As sweat vaporizes on the skin, the body cools down. But when the wet-bulb temperature goes above 97 degrees Fahrenheit, sweat no longer evaporates and cools.

Warmer air can hold more moisture, so as global warming intensifies, the world will get hotter and wetter. This will make extreme heat -- already among the most deadly natural disasters -- even more dangerous.

Why This Matters

Extreme heat is a major public health issue. A study published in May 2020 shows that high wet-bulb temperatures are threatening human survivability. This research found that South Asia, coastal and southwestern North America, and areas around the Persian Gulf may be "nearing or beyond prolonged human physical tolerance.” In 2019, over 345,000 people over 65 died from heat-related deaths. And vector-borne diseases such as dengue, Zika, and malaria are becoming more resilient and widespread due to the world heating up.

Deadly Temperatures Hit India And Pakistan

It’s only May, and South Asia is already experiencing record high temperatures. In India and Pakistan an unprecedented heatwave has put the lives of more than a billion people at risk. In northwest and central India, the average maximum temperatures in April were the highest in over a century.

Over 25 people have died of heat-related causes in the state of Maharashtra in India this year. Estimations from Berkeley Earth showed that this heat is going to get even worse as global warming develops -- average temperatures in India and Pakistan could increase by up to 3.5ºC by the end of the century.

"Even a healthy person exposed to these temperatures for more than seven or eight hours can not survive,” Fahad Saeed, a climate scientist at Climate Analytics, told Inside Climate News.

Tapio Schneider, a professor of environmental science and engineering at the California Institute of Technology, emphasized the deadliness of humid heat in a statement to NBC News: "It’s really a hard limit for survivability. You can die just by sitting there. You don’t need to move or do anything else. There’s simply no way to cool and you overheat.”