New CIRES research drawing on 20 years of satellite data finds that widespread clearing of the Amazon rainforest, particularly along the arc of deforestation, has triggered cloud changes that produce a measurable cooling effect at the top of Earth’s atmosphere. 

When forests are cleared and converted to pastures and grasslands, greenhouse gases that warm the atmosphere are emitted from above and below ground. At the same time, the land surface becomes brighter and reflects more sunlight back into space. Deforestation also enhances cloud formation over cleared areas, which the new study shows roughly doubles the cooling scientists expect to see from surface brightening alone. 

The study adds to growing evidence that clouds are a critical — and still uncertain — component of Earth’s climate system. The researchers hope their work will help improve future climate models and inform land-use decisions.

“The Amazon doesn’t just store carbon,” said Tom Dror, lead author of the study published in Science and a CIRES researcher in NOAA’s Chemical Sciences Laboratory. “It reshapes the atmosphere above it. Understanding that interaction is essential if we want realistic climate predictions.”

Past research has shown that deforestation increases cloud cover over cleared areas by creating differences in surface temperature and moisture transport. But fewer studies have examined the climate effects of these changes in cloud cover. 

In the new study, Dror and her NOAA colleague Graham Feingold analyzed satellite observations of forest cover and the gains and losses of solar energy over the Amazon basin from 2003 to 2022. The researchers compared observations of deforested areas with nearby intact forests under similar climate conditions to tease out local changes caused by land clearing, rather than broader shifts driven by weather patterns or climate trends. 

They found that regions with extensive deforestation reflected more sunlight back into space, cooling the atmosphere above these areas, and that this effect was especially pronounced during the Amazon’s dry season. Interestingly, more than half of that cooling effect came from increases in cloud cover over deforested areas, not from the brightening of the land surface itself. They also found that slightly more infrared radiation, or heat, was lost to space over these areas, enhancing the cooling effect at the top of the atmosphere. 

Across the Amazon basin, deforested areas consistently had more cloud cover and lower cloud tops than surrounding forests. In areas with the most severe forest loss, cloud cover was more than 5 percent higher, while cloud tops were lower by more than 80 meters (260 feet) on average, according to the study. 

Importantly, Dror points out, clouds have been decreasing overall across the Amazon basin, but they are decreasing less in deforested regions. “It’s like the forest’s way of trying to compensate for the pulse of greenhouse gas emissions generated when deforestation occurs,” Dror said.

In spite of the cloud-related cooling, the authors stress that deforestation isn’t a good thing. 

“This study does not suggest that deforestation is good for the climate,” said Graham Feingold, a co-author of the study and a CIRES fellow. “The carbon emissions from forest loss remain a dominant warming influence. What we’re quantifying here is a separate, physical response of the land–atmosphere system that needs to be considered when assessing the overall impact of forest loss.”

“Ongoing research is tying these results to the broader issues of climate change in a warmer and drier Amazon,” Dror said.