Every year, combustion of fossil fuels puff ten billion metric tons of planet-warming carbon dioxide in the atmosphere. And for decades, the Earth’s forests, along with oceans and land, have sucked back about a third, creating a vacuum known as the terrestrial carbon sink. But if deforestation and wildfires ravages the world’s forests, scientists have begun to worry that this crucial balancing act may be in jeopardy.
A study published Wednesday in the journal Nature found that, despite much turbulence, the world’s forests have continued to absorb a steady amount of carbon over the past three decades.
“It appears to be stable, but it actually hides the problem,” said Yude Pan, a senior research scientist at the US Forest Service and the lead author of the study, which included 16 other authors from around the world.
As the Earth’s forests have undergone dramatic changes, with some emitting more carbon than they absorb, Pan warns that better forest management is needed. “I really hope that this study will make people realize how much carbon is lost due to deforestation,” Pan said. “We need to protect this carbon sink.”
About 10 million hectares of forest – an area equivalent to the size of Portugal – is equalized every year, and ever-worsening wildfires almost double that damage. The planet has lost so many trees that experts have warned that forests could soon reach a turning point, in which this crucial carbon vault would emit more planet-warming gases than it absorbs. Some studies have suggested that the Amazon rainforest, often called the lungs of the world already there.
Using data dating back to 1990, the researchers analyzed manual measurements of tree species, size and mass from 95 percent of the globe’s forests to calculate the amount of carbon sequestered over three decades. For each biome studied—temperate, boreal and tropical forests—the researchers considered how long-term changes in the landscape altered the region’s emissions suction.
In the boreal forest, the world’s largest land biome spanning the top of the Northern Hemisphere, the researchers found a dire situation. Over the study period, these cold-loving tree species lost 36 percent of their carbon sink capacity as logging, wildfires, pests and drought ravaged the land.
Some regions fare worse than others: In Canada, wildfires have turned boreal forests into a source of carbon emissions. In Asian Russia forests, similar conditions caused the region to lose 42 percent of its zinc strength.
This is the clear result of decades of worsening fires. A study published in Nature June looked at 21 years of satellite records and was the first to confirm that the frequency and extent of extreme wildfires worldwide has more than doubled. The change is particularly drastic in boreal forests, where these wildfires have become more than 600 percent more common per year.
“I was just shocked by the scale,” said Calum Cunningham, a postdoctoral researcher at the University of Tasmania and lead author of the bushfire study.
Per-Anders Pettersson/Getty
Down near the equator, where tropical forests make up more than half of the world’s tree cover area, the Global Carbon Sequestration Study found a complicated three-way equation. Agricultural deforestation has caused a loss of 31 percent of the old forest’s carbon sink power. But new plant life has reclaimed large tracts of abandoned farmland, and the carbon-sucking power of these younger forests has offset the losses from logging. Although continued deforestation continues to create more emissions, the study found that when these gains and losses are added up, tropical forests are nearly carbon neutral.
So how has the world managed to maintain the overall balancing act? The answer lies in temperate forests, where the carbon sink has increased by 30 percent. The study found that decades of reforestation efforts, mainly through nationwide programs in China, are finally paying off. But the trend may not last. In China, urbanization and logging began cut into tree cover. In the United States and Europe, wildfires, droughts and pests have caused the temperate forest’s carbon sink to drop by 10 percent and 12 percent, respectively.
Forest management efforts, along with the rate of emissions, will determine how this all plays out. Found a paper in Nature last year “striking uncertainty” in the continued potential of carbon storage in American forests, highlighting the need for conservation and restoration efforts.
Chao Wu, a postdoctoral researcher at the University of Utah who led that 2023 study, said that mitigating emissions should be the top priority to solve the climate crisis. “But the other important part is nature-based climate solutions, and the forest will be a very important part of that,” Wu said.
Richard Houghton, a senior scientist at the nonprofit Woodwell Climate Research Center who contributed to the latest sequestration study, says it’s “lucky in a way” that the global forest carbon sink has remained stable.
For this to remain so, Houghton and Pan said that increased restoration efforts and reduced logging are needed in all biomes, and especially in tropical forests, where 95 percent of deforestation takes place. “We don’t have enough conservation,” Houghton said, adding that protecting forest biodiversity and ecosystems contributed to health benefits. “There are always more reasons to do a better job.”
