Wildfires in the rainy, humid Amazon might once have seemed unlikely, but the region is changing. In 2010 and 2015, the Amazon experienced record-breaking droughts and hot weather. Again in 2024, those records were smashed, in part by an extreme El Niño. A new study published in Biogeosciences reveals that the resulting fire season was the worst in 2 decades, pushing fires past deforestation as the Amazon’s biggest carbon emitter.
A Survey of Fire
Deforestation permanently converts forests to other land uses, most often for agriculture. Forest degradation, on the other hand, involves temporary damage to forested land. Degradation can be caused by forces such as droughts, fires, and smaller-scale logging operations and is less well documented than deforestation.
Since 1990, Clément Bourgoin and René Beuchle, both remote sensing researchers at the European Commission’s Joint Research Centre and authors of the new study, have been documenting forest degradation in the Amazon by tracking forest cover in satellite images. “We follow the fate of every single forest, whether it’s undisturbed or degraded,” Bourgoin said. In 2024, they kept up with reports of droughts and wildfires torching vast swaths of the Amazon. But they noticed that there weren’t available statistics on exactly how much forest had been affected.
“We tried to put numbers [to] the diffuse notion that something extraordinary has been happening in terms of forest fires.”
“We felt a clear lack of information that was there,” said Beuchle. “So we tried to put numbers [to] the diffuse notion that something extraordinary has been happening in terms of forest fires.”
The researchers’ tropical moist forest dataset classifies forest disturbances as either deforestation or degradation. They combined this dataset with the Global Wildfire Information System dataset, which uses thermal sensors on satellites to detect wildfires. By overlaying the two datasets, the researchers could align regions of large-scale forest degradation with those that had experienced forest fires.
A 2-Decade Record
The researchers expected to see forest degradation from fire, but Bourgoin said they were “quite surprised about the magnitude.” The analysis revealed that 3.3 million hectares of forest—approximately the same area as the state of Maryland—were affected by fires last year. Though deforestation in 2024 actually dropped by 20% compared to the average from 2019 to 2023, forest degradation, linked mainly to fires, increased by 400%. By area, forest degradation surpassed deforestation by more than 4 times in 2024, marking a shift in the threats to the Amazon’s health.
“We were unprepared for the sheer mass of burnt forest that we found in Bolivia. It was a shock.”
Brazil and Bolivia suffered the worst losses. In 2024, Bolivia lost 9% of all its intact forest to fire. “We were unprepared for the sheer mass of burnt forest that we found in Bolivia,” Beuchle said. “It was a shock.” Brazil saw the highest level of forest degradation on record.
The researchers estimate that the fires released 791 million tons of carbon dioxide into the atmosphere, a sevenfold increase from the average of the preceding 2 years. This amount of carbon dioxide marks an ominous transition: that of wildfire emissions surpassing deforestation emissions. The consequences also extend far beyond a single year, as burnt forests may continue to emit carbon for 7 years or longer after a fire.
“Everyone knew [2024] was going to break the records 6 months before” the El Niño even started, said Bernardo Flores, an ecologist at the Instituto Juruá and the University of Santiago de Compostela who wasn’t involved in the study. He said the study was important to quantify the extent of fire damage and show how strong El Niños will increase the burnt area. “That’s good science.”
“Fires are probably one of the main drivers of degradation that could lead to a tipping point.”
Flores also noted a warning in the new study’s data that will make fire prevention even more crucial. The degradation caused by burning makes the forest more susceptible to burning again in the future, so the huge regions of the Amazon that burned in 2024 could contribute to worsening fires in future drought years. This feedback cycle could make it harder for the Amazon forest to regenerate. “Fires are probably one of the main drivers of degradation that could lead to a tipping point,” after which the forest would no longer be able to regenerate and would become permanently degraded, Flores said.
Public and governmental awareness of the magnitude of the wildfires is an especially important step in avoiding the tipping point in the Amazon, where nearly all fires are human caused—either for agricultural purposes or to facilitate illegal deforestation. Next, the researchers plan to track how past disturbances may influence future degradation and to study how well the regions that burned in 2024 recover over time. Still, for now, they are making their data publicly available to help guide fire-safe policies in the area in the hopes of preventing irreversible damage to the Amazon. “It helps to put degradation on the agenda,” Bourgoin said.
—Andrew Chapman (@andrewchapman.bsky.social), Science Writer