Scientists have been alarmed in recent years as global temperatures continue to rise at an unprecedented rate. Both 2023 and 2024 saw temperatures around 1.5°C above pre-industrial levels, a threshold that climate agreements have long sought to avoid. Although factors such as El Niño and reduced air pollution, which previously helped cool the planet, have been expected to contribute to this warming, experts say these alone do not fully explain the record-breaking heat.

Two recent studies suggest a new explanation: a decline in cloud cover. Scientists warn that fewer clouds could be triggering a feedback loop that accelerates global heating, making it even harder to curb rising temperatures.

This follows a recent revelation, that the Earth's increasing energy imbalance, the difference between the heat the planet absorbs and the amount it radiates back into space, is contributing to the climate crisis. This imbalance drives global warming, and as it grows, temperatures are expected to continue rising.

“We have added a new piece to the puzzle of where we are headed,” Helge Goessling, a climate physicist at the Alfred Wegener Institute in Germany and lead author of one of the studies, told the Washington Post.

The role of clouds in climate change

For decades, researchers have struggled to incorporate cloud behaviour into large-scale climate models. Clouds influence the climate in two opposing ways. Their bright surfaces reflect sunlight, which cools the planet. However, they also trap heat by reflecting infrared radiation back to the surface, similar to the role of greenhouse gases in the atmosphere.

The overall impact of clouds on global temperatures depends on their type and altitude, say the scientists. High-altitude, thin cirrus clouds tend to contribute to warming, while low, dense cumulus clouds have a cooling effect.

“Clouds are a huge lever on the climate system,” Andrew Gettelman, a scientist at the University of Colorado at Boulder, told the newspaper. “A small change in clouds could be a large change in how we warm the planet.”

Goessling’s study, published in Science, examined how cloud cover has evolved over the past decade. The findings revealed a significant drop in low-altitude cloud formation, which has made the planet less reflective. In 2023, the Earth’s reflectivity, or albedo, reached its lowest point since 1940.

In simple terms, the planet is darkening.

Goessling and his co-authors estimate that this loss of cloud cover contributed 0.2°C to 2023’s record-high temperatures. This additional warming closely matches the amount that had remained unexplained by other climate drivers. “This number of about 0.2 degrees fairly well fits this ‘missing warming,’” Goessling said.

What’s causing the decline in cloud cover?

Scientists are still working to determine the precise reasons behind the decrease in clouds. One theory is that lower air pollution levels are playing a role. Airborne particles, or aerosols, provide a surface for water droplets to cling to, aiding cloud formation. As air pollution has declined, particularly in regions where emissions controls have improved, fewer particles may be available to help sustain cloud cover.

Another possibility is that rising temperatures themselves are making it harder for some clouds to form. Moist stratocumulus clouds, which typically develop just below a dry atmospheric layer about a mile above the surface, depend upon stable conditions. Warming temperatures may be causing hot air from below to mix with this dry layer, disrupting the environment that these clouds need to persist.

However, cloud changes are difficult to predict, and climate models do not always show consistent patterns. “It’s really tricky,” Goessling told the Post.

NASA Research Supports Cloud Decline Findings

A separate study presented by NASA researchers at a recent scientific conference supports Goessling’s findings. NASA’s research indicates that some of the Earth’s cloudiest regions have been shrinking over the past two decades.

George Tselioudis, a climate scientist at NASA’s Goddard Institute for Space Studies in the US and lead author of the study, found that three key cloud zones have narrowed since 2000: one stretching around the equator and two located in mid-latitude storm belts in both hemispheres. The contraction of these cloud-heavy regions has made the Earth less reflective, contributing to rising temperatures.

Tselioudis and his team estimate that cloud cover in these areas has been shrinking by about 1.5% per decade. “We’ve always understood that the cloud feedback is positive—and it very well could be strong,” Tselioudis told the Post. “This seems to explain a big part of why clouds are changing the way they are.”

The risk of a dangerous feedback loop

If the loss of clouds is part of a self-reinforcing feedback loop, experts warn, global temperatures could rise even faster than expected. Each consecutive hot year strengthens concerns that climate models may have underestimated the upper limits of future warming. Some researchers now believe that the world could surpass the critical Paris Agreement 1.5°C threshold later this decade—much sooner than previously anticipated.

A rise beyond this level would have dire consequences, leading to more intense heatwaves, droughts, and extreme weather events for billions of people worldwide, credible experts agree.

The urgency to understand these trends has grown as warming continues. Scientists are racing to determine whether cloud cover will continue to decline—and if so, how quickly. “We are kind of in crunch time,” Goessling said. “We have a really strong climate signal—and from year to year it’s getting stronger.”

What’s next?

Researchers are calling for further studies to refine climate models and assess the long-term implications of shrinking cloud cover. If fewer clouds continue to drive warming, efforts to limit global temperature rise may need to be even more aggressive than previously thought.

Scientists are also urging policymakers to consider the potential effects of cloud changes when planning climate mitigation strategies. Without urgent action, the accelerating loss of cloud cover could make it even harder to slow down climate change in the coming decades.