As the Saying Goes, ‘It’s Not the Heat, It’s the Humidity.’ And It’s Killing Us Faster Than You Think.

As someone who just decamped from New York City to the Pacific Northwest, you could probably call me a climate refugee.

I spent most of my life in New York, and watched as summers became ever more unbearably hot and soupy. And I wasn’t just imagining it.

“It’s almost as if the entire East Coast has shifted south,” David Leonhardt wrote last week in a handy but frightening look at the region’s global warming. New York summers now resemble ones in Philadelphia, while Philadelphia’s have become hotter than Washington’s a few decades ago, and so on down the line, from Maine to Florida.

So, recently, I made a promise to myself — I would not live through another New York summer ever again if I could swing it. Hence my move to temperate Seattle (which, disturbingly, just had a record-setting heat wave in June).

Of course, my discomfort in the Northeast is miniscule next to that of people living in places with ruthless brutal heat and humidity, like India, Mexico, or Southeast Asia. By the end of this century, in places like these, people may not be able to survive the punishing temperatures, scientists say.

Because, as the saying goes, “It’s not the heat, it’s the humidity.”

The combination of the two is called “wet-bulb temperature,” which, when higher than our own body temperature, is a point at which we can no longer “sweat fast enough to prevent overheating,” Radley Horton, a professor at Columbia University’s Lamont-Doherty Earth Observatory, told The Washington Post.

“Heat index is about comfort,” Hank Green, a science educator, explained on TikTok. “Wet bulb is about survival.”

When your body can no longer sweat enough to cool itself, your organs start to fail. (See this incredible multimedia feature from The Washington Post to understand in detail how this happens.)

“Humid heat risks are grossly underestimated today and will increase dramatically in the future,” said Horton. “As locations around the world experience previously rare or unprecedented extremes with increasing frequency, we run the risk that our previous messaging about extreme heat risk — already woefully inadequate — will fall further short of the mark.”

And scientists have a warning that goes against what we’d normally think would help us cool down: being by the ocean in a hot city could, rather than lower your body temperature, kill you because of the wet-bulb effect.

“If you’re sitting in a city along the Persian Gulf, the sea breeze could be a deadly breeze,” Horton said.

And, as usual in the climate crisis, the poorest people are the most likely to be affected by this nightmare aspect of climate change. Think farm laborers in sweltering California, or migrant construction workers in Qatar, toiling under an unrelenting sun in 111-degree temperatures.

A 2019 U.N. study revealed that the Qatari workers’ core body temperature was normal for most of their shift. But, “one in three workers performed up to five percent of their job while hyperthermic (core temperature 38.0-38.4°C) [as high as 101 degrees], and this can account for up to 30 minutes during a work shift.”

This is a future war of the haves and have-nots.

Impoverished people can’t necessarily afford an air-conditioner (or have the electrical capacity to connect one), or a cooled-off pool, or anything else that would help them escape the heat.

We’re racing toward a muggy, awful future, fast. And it’s going to be the neediest people in the world who get there — and potentially die — first.