Horizon, person on beach bending over in heat

Extreme heat calls for extreme action

Climate change is scorching the globe, including areas previously thought to be low risk.

And the firsts keep coming: all-time highs across a record number of cities, all-time record-high days in succession, plus unheard-of high nighttime lows that take an especially brutal toll on those without air conditioning, outdoor workers, older people and anyone with health issues.

June, July and August 2023 were the hottest summer months on record globally, and 2023 was the hottest year ever recorded.

How greenhouse gases fuel heat waves

There is a clear connection between climate change and heat waves: Climate change has likely doubled the probability of heat waves globally since the 1950s.

In addition to trapping heat in the atmosphere, climate change can make heat waves worse via changing air patterns that set up ideal conditions for “heat domes,” where hot air is trapped on Earth’s surface by high pressure buildup in the atmosphere.

And research shows that the deadly temperatures of the June-July 2023 heat waves in the U.S., Mexico, Southern Europe and China would have been virtually impossible without human-caused climate change.

Ilissa Ocko

Scientists continue to show how human‑caused climate change has made dozens of heat waves across the globe hotter and more likely to occur.

— Ilissa Ocko, Senior Climate Scientist

Hotter air means more — and more persistent — droughts in already drought-prone areas due to increased evaporation. Across the western U.S., the overall extent of drought is at its highest level since the U.S. Drought Monitor began in 2000. That will likely trigger even more and worse wildfires than the catastrophic blazes we’ve already seen.

For farmers and others who work outdoors, extreme heat endangers their livelihoods as well as their health.

And rising temperatures threaten the availability of food for everyone by increasing the likelihood of crop failure as well as the spread of non-native insects and insect-borne diseases that attack people, plants and animals.

For personal and public-health planning, it’s important to keep in mind that sweat doesn’t cool you — evaporation does. And humidity reduces evaporation.

At just 70% humidity, a usually manageable 96 F turns into a heat index (heat + humidity = effective heat) of 126 F. And that’s in the shade. Full sunshine can add 15 degrees to the heat index — turning a 70% humidity, 96-degree day into a 141-degree day in terms of sweat’s ability to do its job.

It’s not too late to take action

At this point, small steps will not get us where we need to be.

We must eliminate greenhouse gas emissions aggressively, without delay, and remove the excess carbon in the atmosphere that is driving these ever-more-destructive changes in our climate.

Learn more about extreme weather

Our extreme heat experts

We bring wide-ranging perspectives and skills to our work on extreme heat. Meet a few of the people driving this work.

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Anne Marie Borrego

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