Story at a glance

  • A new paper just released by researchers at Columbia University has discovered an increase in previously rare bouts of extreme heat and humidity in locations around the world.
  • Some of these weather events have reached temperature levels so high that they are inhospitable to humans.
  • Our bodies are only able to withstand a certain level of heat before we are at risk for stroke or death, and humidity only exacerbates those risks.

Startling new research conducted by scientists at Columbia University has disproved prior projections showing that later in the century, in parts of the tropics and subtropics, a warming climate could cause combined heat and humidity to reach levels rarely, if ever, experienced before by humans. 

The projected conditions would not only ravage economies, but possibly even surpass the physiological limits of human survival. 

According to the new study, such conditions projected decades into the future are actually already appearing today. The study identifies thousands of previously rare or unprecedented bouts of extreme heat and humidity in Asia, Africa, Australia, South America and North America, including in the U.S. Gulf Coast region. In some areas such as the Persian Gulf, researchers have even spotted more than a dozen recent brief outbreaks surpassing the theoretical limit of what human bodies are able to survive. While these outbreaks have been confined to localized areas and lasted just hours, they are increasing in frequency and intensity, say the authors of the study. 

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“Previous studies projected that this would happen several decades from now, but this shows it’s happening right now,” said lead author Colin Raymond, who did the research as a PhD. student at Columbia University’s Lamont-Doherty Earth Observatory. “The times these events last will increase, and the areas they affect will grow in direct correlation with global warming.”

The areas most at risk have high populations

Analyzing data from weather stations from 1979 to 2017, the authors of the study found that extreme combinations of heat and humidity doubled over the study period, with repeated incidents appearing in much of India, Bangladesh and Pakistan. Other hot spots included northwestern Australia and along the coasts of the Red Sea and Mexico’s Gulf of California. The highest, potentially fatal, readings were spotted over ten times in cities in Saudi Arabia, Qatar and the United Arab Emirates, which have combined populations of more than 3 million. Parts of Southeast Asia, southern China, subtropical Africa and the Caribbean were also hit.


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A previous study of temperature and humidity records by MIT emphasize these findings: While earlier reports showed that the survivability limit would start to be exceeded occasionally in the Persian Gulf region by the end of this century, actual readings there in the summer of 2015 showed that the 35-degree wet-bulb limit had almost been reached already, suggesting that such extremes could begin happening earlier than projected. The summer of 2015 also produced one of the deadliest heat waves in history in South Asia, killing an estimated 3,500 people in Pakistan and India.

The study also found that, despite these facts, India and China remain two countries where emission rates of greenhouse gases continue to rise, driven mostly by economic growth. “I think these results pose a dilemma for countries like India,” says Elfatih Eltahir, the Breene M. Kerr Professor of Civil and Environmental Engineering at MIT. “Global warming is not just a global problem — for them, they will have some of the hottest spots on the planet.”

In today’s climate, about 2 percent of the Indian population sometimes gets exposed to extremes of 32-degree wet-bulb temperatures. According to the study by MIT, by 2100 that will increase to about 70 percent of the population, and about 2 percent of the people will sometimes be exposed to the survivability limit of 35 degrees. 

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The newest study by Columbia University found that the southeastern United States also saw the same extreme conditions dozens of times, mainly near the Gulf Coast in Louisiana, Mississippi, Alabama, eastern Texas and the Florida Panhandle. The worst spots were New Orleans and Biloxi, Miss., — not surprising, considering incidents tended to cluster on coastlines along confined seas, gulfs and straits, where evaporating seawater provides abundant moisture to be sucked up by hot air. In some areas further inland, moisture-laden monsoon winds or wide areas of crop irrigation appear to play the same role.


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The researchers claim that previous climate studies failed to recognize these quick-but-deadly, targeted incidents because climate researchers usually look at averages of heat and humidity measured over large areas and over several hours at a time. Raymond and his colleagues instead drilled directly into hourly data from 7,877 individual weather stations, allowing them to pinpoint shorter-lived bouts affecting smaller areas. 

What humid heat does to the body

Anyone who’s walked outside on an unusually muggy day knows it to be true: Humid heat is harder to handle than the “dry” kind. Why? Well, because normally the body is able to cool itself down by opening pores on the skin and releasing water and salts, and as that water evaporates it transfers the body’s heat to the air. 

Here’s the tricky part regarding humidity — the rate at which sweat evaporates also depends on how much water is already in the air, so if the air is dry then your body has an easier job of wicking that sweat away and cooling yourself down. Humid days, on the other hand, happen when the air is already saturated with water, so sweat evaporates more slowly.

According to a lecturer at MIT, this explains why it feels so much hotter to be exposed to high humidity. When relative humidity reaches a high enough level, the body’s natural cooling system simply can’t work. Sweat evaporates very slowly, if at all, and the body heats up. In extreme cases, people begin to suffer from heat cramps or heat stroke, which is basically organ failure as the body begins to cook itself.

This drastic difference in the way our body handles types of heat is explained by the heat index, which provides warnings for weather conditions that will make heat stroke more likely. For instance, the body experiences 88-degree Fahrenheit weather with 85 percent humidity as if it were actually 110 degrees — not very pleasant.

In the most extreme instances, our body’s natural response to extreme heat could stop. In that case, unless one can retreat to an air-conditioned room, the body’s core heats beyond its narrow survivable range, and organs begin to fail. Even a strong, physically fit person resting in the shade with no clothes and unlimited access to drinking water would die within hours.

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None would remain unaffected

An investigation last year by the website InsideClimate News revealed that cases of heat stroke or heat exhaustion among U.S. troops on domestic bases grew 60 percent from 2008 to 2018. Seventeen soldiers died, almost all in the muggy U.S. Southeast. High-humidity heat waves in Russia and Europe, where far fewer people have access to air conditioning, have already killed tens of thousands.

“We may be closer to a real tipping point on this than we think,” said Radley Horton, a Lamont-Doherty research scientist and coauthor of the paper. Horton co-authored a 2017 paper projecting that such conditions would not take hold until later in the century.

While air conditioning may blunt the effects in the United States and some other wealthy countries, there are limits. When workers are forced indoors for longer periods of time, necessary industries such as farming and commerce would be halted, even in rich nations where there is wider access to air conditioning. 

Kristina Dahl, a climatologist at the Union of Concerned Scientists who led a study last year warning of increasing future heat and humidity in the United States, said the new paper by Columbia shows “how close communities around the world are to the limits.” 


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Published on May 08, 2020