Photo: Genaro Molina / Los Angeles Times via Getty Images

A pair of scientific studies published this week tracked the dangerous increase in heat and humidity from climate change so far — and projected a future that could be too hot for billions of people.

Why it matters: Don't forget the warming in global warming. A more populous humanity will be hard-pressed to adapt to a world where large stretches of land are simply too hot to live in easily.

A study published in Science Advances on May 8 identified thousands of unprecedented periods of extreme heat and humidity in areas around the world, including in the U.S. Gulf Coast region.

  • The study analyzed weather data and found extreme heat and humidity combinations doubled between 1979 and 2017.
  • Along the already brutally hot Persian Gulf, there were more than a dozen times when the mix of high temperatures and humidity temporarily exceeded the theoretical human survivability level.

Of note: Scientists assess the heat and humidity combination using what is known as wet-bulb temperature, which is literally measured by wrapping a thermometer in a wet cloth.

  • A wet-bulb temperature of 95 F is lethal after about six hours.

Another study published in the Proceedings of the National Academy of Sciences on May 4 looked at the next half-century and found one-third of the world's population could end up living in areas considered unsuitably hot for human beings.

  • While today only about 25 million people live in the world's hottest areas, with mean annual temperatures above 84 F, by 2070 extreme heat could have spread to multiple regions, including parts of India, the Middle East and Australia.
  • Coupled with expected population growth, that could mean as many as 3.5 billion people living under extreme heat stress.

Yes, but: The study is based on what the authors called a worst-case scenario, where little is done to curb greenhouse gas emissions. And as the global population gets richer — assuming that trend continues — more people will be able to afford air conditioning, though such adaptation would add to carbon emissions.

The bottom line: The studies show that the livable climate we've taken for granted for thousands of years is not the one we'll be enduring in the future.

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