Dangerous levels of heat and humidity have been recorded around the globe 50 years earlier than expected, according to a study published Friday that was led by Columbia University researchers.
The findings add to growing concerns that climate change will make certain parts of the Earth uninhabitable, spurring a drastic increase in climate refugees and threatening to create international strife and economic damage.
In the study, published in the journal Science Advances, climate scientists analyzed four decades of hourly data from nearly 8,000 weather stations across the globe using so-called wet bulb readings to document potentially fatal bouts of hot, wet air. The analysis provides a far-more detailed picture of how dangerously warm weather has spiked in certain areas than previous research that looked at broader regions.
Wet bulb temperature is similar to heat index in that it takes both heat and humidity into account to calculate how hot the air feels — and the effect it can have on the human body. Scientists widely accept 95 degrees as the highest wet bulb temperature the human body can withstand, though this depends on many factors and may be lower for people who work outside, the elderly and people on certain medications or who have pre-existing conditions.
“The wet bulb temperatures tell us if the weather conditions around us allow the body to cool itself down and stay safe,” said Rachel Licker, a senior climate scientist at the Union of Concerned Scientists, who was not involved in the study.
Previous research had looked at wet bulb temperatures taken from multiple points over large geographical areas across the globe. By looking at hyper-local weather data points, the new research more accurately reflects localized spikes in heat and humidity, finding extremes that researchers didn’t expect to occur until at least 2070.
The study found that local instances of extreme humid heat — a wet-bulb temperature of 80.6 degrees or above — doubled from 1979 to 2017.
Scientists previously believed that wet bulb temperatures rarely reached 87.8 degrees, but the new study found recordings of that temperature 1,000 times. Readings of 91.4 degrees — thought to almost never occur — were recorded almost 80 times. And the readings exceeded the theoretical human survivability limit of 95 degrees more than a dozen times.
These extreme spikes in hot, wet air were brief, only occurring for an hour or two at a time, and were confined to hyper-local areas. But the researchers expect these instances to become more frequent as global temperatures continue to rise.
“We’re seeing really strong upward trends and already, places are crossing this dangerous threshold. It’s not something that will just happen at the end of the century. It has already been happening,” said Radley Horton, Lamont associate research professor at the Columbia University Earth Institute, who co-wrote the study.
The Southeastern United States was a hotspot for these temperature spikes, especially near the areas of Texas, Louisiana, Mississippi, Alabama and Florida that lie along the Gulf Coast. New Orleans and Biloxi, Mississippi, were the epicenters and the heat stretched inland as far as Arkansas.
Coastal regions of the Middle East, India, Bangladesh, Pakistan, northwestern Australia and the regions bordering the Red Sea and the Gulf of California are also already seeing the extreme temperatures thought to be reserved for 50 years from now.
“Even a small amount of warming can mean a lot more 100-degree days than we had before,” Horton said. “Humans are very sensitive to small changes in temperatures, and we’re starting to push up against the brink of what we have evolved to be able to handle.”
Heat alone does not pose as big a threat to human health as the combination of hot and humid air does. That’s because the combination essentially blocks the body’s ability to cool itself.
“As humidity increases and approaches 95 percent, sweating becomes ineffective because the air is already saturated with water vapor and can’t hold any more,” said Dr. Robert Dubrow, faculty director of the Yale Center on Climate Change and Health.
Without access to a cooler spot, such as an air-conditioned room or cool water, the body quickly overheats. Overheating exasperates underlying conditions and puts stress on elderly people who are often also taking several types of medications that could hinder their ability to withstand the stress, Dubrow said.
Extreme heat and humidity can also trigger heat stroke, a medical emergency that is often fatal for even healthy people. Even the fittest athletes are not immune. Former New York Giants offensive lineman Mitch Petrus died of heat stroke last year when the heat index in Arkansas, where he was working for his family’s towing business, hit 103 degrees.
Summer is coming
The National Oceanic and Atmospheric Administration predicts above-average summer temperatures and rainfall will affect most of the U.S. this summer, a recipe for hot and humid weather. The forecast has experts worried that the current coronavirus pandemic will either force people to stay in unair-conditioned homes rather than seek out cooling stations, or force them into overcrowded public spaces, as was the case during a recent heat wave in Orange County, California.
“In cities, people without air-conditioning are going to want to get out of their houses, and if they are crowded into public spaces, there will be the same issue with social distancing,” Dubrow said.
The new research provides clearer insight into how extreme weather driven by climate change is already affecting human life, with or without a global pandemic.
“Climate change is here and now," Licker said. "We often talk about it being something that is going to happen in the future, but this is showing that the heat that we thought was not going to happen for decades is already happening and has been increasing for the past 40 years."
Follow NBC HEALTH on Twitter & Facebook.