A combination of heat and humidity so extreme that it’s unendurable isn’t just a problem for the future — those conditions are already here, a new study finds. Off-the-chart readings that were previously thought to be nearly nonexistent on the planet today have popped up around the globe, and unyielding temperatures are becoming more common.
Extreme conditions reaching roughly 115 degrees Fahrenheit on the heat-index scale — a measurement of both heat and humidity that’s often referred to as what the temperature “feels like” — doubled between 1979 and 2017, the study found. Humidity and heat are a particularly deadly combination, since humidity messes with the body’s ability to cool itself off by sweating. The findings imply that harsh conditions that scientists foresaw as an impending result of climate change are becoming reality sooner than expected.
“We may be closer to a real tipping point on this than we think,” Radley Horton, co-author of the new study published today in the journal Science Advances, said in a statement. His previous research had projected that the world wouldn’t experience heat and humidity beyond human tolerance for decades.
More intense and frequent heat events are one of the symptoms of climate change, a lot of research has shown. But most of those studies were based on readings that looked at averages over a wide area over a long period of time. Instead, Horton and his co-authors looked closely at hourly data from 7,877 weather stations around the world. They used the “wet bulb” centigrade scale, which measures other factors such as wind speed and solar radiation on top of heat and humidity.
That’s how they found more than a thousand readings of severe heat and humidity, reaching wet bulb readings of 31 degrees Celsius, that were previously thought to be very rare. Along the Persian Gulf, they saw more than a dozen readings above what’s thought to be the human tolerance limit of 35 degrees Celsius on the wet bulb scale. That’s the highest wet bulb reading that scientific literature has ever documented. In 2015, the city of Bandar Mahshahr in Iran experienced a wet bulb reading just under 35 degrees Celsius. At more than 160 degrees Fahrenheit on the heat-index scale, that’s about 30 degrees higher than where the National Weather Service’s heat-index range ends — and it’s a scenario that climate models hadn’t forecast to happen until the middle of the century.
Spells of extreme humid heat were also witnessed across Asia, Africa, Australia, South America, and North America and were generally clustered along the coasts. The US Gulf Coast was particularly hard-hit. The region saw dozens of instances of conditions reaching levels not expected to take place for decades. Severe conditions only lasted hours and were often only in small areas, but these bouts are becoming more frequent and more intense, the researchers say.
They make the case that future studies ought to take a similarly localized look to get a better understanding of how climate change is playing out in communities that will feel the crunch ahead of the rest of the world. A Pulitzer prize-winning series by The Washington Post took this sort of approach in a series about places where average temperatures have already risen 2 degrees Celsius, the threshold at which the Paris climate accord aims to keep the globe from surpassing.
“If you zoom in you see things that you don’t see at a larger scale,” says Colin Raymond, lead author and a postdoctoral researcher at NASA’s Jet Propulsion Laboratory. “At the smallest scale, it’s more intense.” One of the limitations to their study, according to Raymond, is that there are places across the globe that simply lack weather stations. So what they were able to document could be happening at an even wider scale, there just aren’t tools in place yet to make those measurements everywhere.
Extreme heat already kills more people in the US than any other weather-related event.
In 50 years, between 1 to 3 billion people could find themselves living in temperatures so hot that they’re outside the range in which humans have been able to thrive, found another study published this week. Just how many billions will face that future depends on what action is taken now to stop the planet from dangerously overheating.
