In 2023 and 2024 the world’s forests absorbed only a quarter of the carbon dioxide they did in the beginning of the 21st century, according to data from the World Resources Institute’s Global Forest Watch.
Those back-to-back years of record-breaking wildfires hampered forests’ ability to tuck away billions of tons of carbon dioxide, curbing some of the global warming caused by emissions from burning fossil fuels.
Those two years also marked the first time wildfires surpassed logging or agriculture-driven deforestation as the biggest factor lowering forests’ carbon-capturing ability. It’s an emerging pattern that’s different from the last big drop, in 2016 and 2017, which was largely the result of increased deforestation for agriculture.
Carbon dioxide, a greenhouse gas, acts as a blanket in the atmosphere, trapping the sun’s heat and warming the environment. In some places, rampant burning and deforestation have tipped the scales, turning forests into a source of carbon dioxide emissions instead of a tool for capturing them.
Removing carbon from the atmosphere is “an unpaid service by trees and forests toward slowing climate change,” said Nancy Harris, research director of both WRI’s Global Forest Watch and Land and Carbon Lab. “When we lose that function, we have to work even harder to cut emissions.”
So far, Dr. Harris said, 2025 doesn’t seem far behind the trend. The year started with devastating blazes across Los Angeles and by midsummer, saw major wildfires that raged across Europe and broke records in Korea. And this week, Canada is entering the peak of fire season and the country is already on track for its second-worst year of wildfires on record.
Other recently published studies suggest that climate change is making extreme-forest-fire years more common, and the worst events more frequent and intense. “These climate extremes are making it harder for forests to do their job,” Dr. Harris said.
Each forested region faces unique pressures. In Bolivia, agriculture-driven deforestation left the Amazon teetering for most of the past two decades between being a source of carbon dioxide, and a sponge pulling it out of the air. But, according to the new data, large wildfires in 2024 firmly tipped the scales and turned the region into a net source of emissions.
In the greater Amazon region, over half of which is in Brazil, years of widespread drought have primed trees to burn, driving forest loss even when logging slows down. The region’s increasingly prevalent wildfires are worsening what the researchers call an “arc of deforestation” visible on satellite data maps.
And across the northern reaches of Canada, Russia and Alaska, boreal forests — one of the world’s oldest and largest vaults of locked-away carbon — are at risk from fires.
In 2023 and 2024 combined, nearly 24 million hectares of Canada’s forests burned, filling large swaths of skies over North America with smoke and flipping the region to an overall source of emissions. Some 74 percent of these fires happened in peatlands, a kind of boggy landscape that can smolder for months on end, creating “zombie fires” that eat through the carbon-rich soil.
“We’re reaching the point where global warming is feeding the warming,” said Werner Kurz, an emeritus scientist for the Canadian Forest Service who was not involved with the analysis. As the world warms, causing forests to burn and release more emissions, he said, it creates a feedback loop that paves the way for more heat.
Not all forests are dwindling. In Appalachia, woodlands that were logged generations ago have now become a powerful carbon sponge after being abandoned and allowed to regrow as wilderness in the mid-20th century. In China, decades of nationwide tree-planting efforts have restored the region’s ability to store carbon.
“There are bright spots on the planet that are absorbing carbon more, but the scales are a little tipped,” Dr. Harris said. “Regrowing forests, restoration and tree planting are definitely part of the solution, but we also have to stop this ongoing loss.”
In the past 20 years, Southeast Asian forests became a source of emissions, driven by booming oil palm plantations and the draining of peatlands. In central Africa and Madagascar, the clearing and burning of forests to make room for small-scale agriculture has also created emissions hot spots.
According to W.R.I., “secondary” growth forests, those at least 20 years of age, are responsible for two-thirds of the amount of carbon that trees have captured in the past 25 years. And younger ones make up just 2 percent of trees, but their carbon-hungry growth spurts account for about 6 percent of carbon that they pull out of the air each year.
It can take many decades for a reforestation project to grow enough to replace the carbon that was in an eliminated old-growth forest, said Richard Birdsey, a senior scientist at the Woodwell Climate Research Center who was not involved with the new analysis, which is why researchers refer to the loss as a “carbon debt.”
According to Dr. Kurz, older forests, like those in Canada’s boreal, may grow slowly and absorb less carbon annually, but they represent decades of already-captured carbon. “The trouble is now fires are releasing really old carbon back into the atmosphere that took centuries to accumulate in the forest floor and soil,” Dr. Kurz said.
Sachi Kitaijma Mulkey covers climate and the environment for The Times.
Harry Stevens is a Times reporter and graphics editor covering climate change, energy and the natural world.
The post For 1st Time, Fires Are Biggest Threat to Forests’ Climate-Fighting Superpower appeared first on New York Times.
