• Posted February 19, 2025

Scientists Have New Theory About Record Heat

WEDNESDAY, Feb. 19, 2025 (HealthDay News) — You aren't imagining it: The cloud cover isn't what it used to be, and scientists say it is helping fuel Earth's hottest temperatures on record.

Global temperatures clocked in at roughly 1.5 degrees Celsius above predindustrial averages in both 2023 and 2024. 

While climate experts say some of the rise can be explained by a weather pattern called El Niño that causes unusual Pacific Ocean warming along with decreasing air pollution that cools Earth, they agree that those factors alone don't explain the record heat.

Simply put: Earth is taking in more heat than it's releasing -- an energy imbalance that drives global warming.

Enter a new round of studies that suggest fewer clouds are playing a big role.

"Clouds are a huge lever on the climate system," Andrew Gettelman, an affiliate scientist at the University of Colorado at Boulder told The Washington Post, reacting to the studies. "A small change in clouds could be a large change in how we warm the planet."

A German team recently reported in the journal Science on the effects of a dramatic drop in low-altitude cloud cover.

Cloud cover matters: Not only do clouds reflect sunlight and cool Earth off, they also reflect infrared radiation back to the Earth's surface.

Which part of that functioning wins out, The Post reported, depends on the type of cloud and how high it is. And when it comes to cooling things off, people know from experience that low, fluffy cumulus clouds do a better job than high, thin cirrus clouds.

At a recent science conference, a team of NASA researchers reported that three areas of clouds have narrowed significantly -- one around the equator and two around stormy mid-latitude regions in the northern and southern hemispheres. 

Cloud cover in these regions is shrinking by about 1.5% per decade, helping fuel warming, according to a preprint of their research. It is under review at Nature Portfolio and should be regarded as preliminary until published.

Lead researcher George Tselioudis, a climate scientist at NASA's Goddard Institute for Space Studies, told The Post that general warming may be constraining these cloud-heavy regions -- thus heating the planet.

"We've always understood that the cloud feedback is positive — and it very well could be strong," he said. "This seems to explain a big part of why clouds are changing the way they are."

Scientists warn that if these changes are part of a feedback loop, more extreme heat is likely on the way. Many now agree that global temperatures will reach the high end of projections. 

"We are kind of in crunch time," climate physicist Helge Goessling told The Post in a video interview. 

He's a scientist at the Alfred Wegener Institute in Germany who led a study recently published in the journal Science that analyzed how the cloud cover has changed in the past decade.

His team looked at a characteristic called albedo -- the light reflected by a surface to relative to the light that hits it. 

The key finding: Earth's albedo was the lowest since 1940, and that contributed about 0.2 degrees Celsius to record heat in 2023. That, researchers pointed out, is roughly equivalent to levels of warming that scientists have been unable to explain.

"This number of about 0.2 degrees fairly well fits this 'missing warming,'" Goessling told The Post. 

Researchers aren't sure why this is happening -- and climate models show different changes that make predictions "really tricky," Goessling said.

No matter the cause, he said, one thing is certain: "We have a really strong climate signal -- and from year to year it's getting stronger." 

More information 

Learn more about climate change at NASA.

SOURCE: The Washington Post, media report, Feb. 14, 2025