Surprisingly, forests are still absorbing as much carbon as they did 30 years ago. But there’s a catch.

By Sachi Kitajima Mulkey, Grist

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Every year, burning fossil fuels releases tens of billions of tons of global-warming carbon dioxide into the atmosphere. And for decades, Earth’s forests, along with its oceans and soils, have been absorbing about a third of that, creating a void known as the terrestrial carbon sink. But as deforestation and wildfires ravage the world’s forests, scientists are beginning to worry that this crucial balance is under threat.

A study published Wednesday in the journal Nature reveals that, despite many upheavals, the world’s forests have continued to absorb a constant amount of carbon over the past three decades.

“It looks stable, but in reality it may be masking the problem,” said Yude Pan, a senior research scientist at the U.S. Forest Service and lead author of the study, which included 16 co-authors from around the world.

As the world’s forests have undergone drastic changes, with some releasing more carbon than they absorb, Pan warns that better forest management is needed. “I really hope this study makes people aware of how much carbon is lost through deforestation,” Pan said. “We need to protect this carbon sink.”

Every year, nearly 10 million hectares of forests—an area the size of Portugal—are cleared, and increasingly intense fires are nearly doubling that damage. The world has lost so many trees that experts warn that forests could soon reach a tipping point, at which this vital carbon reserve emits more greenhouse gases than it absorbs. Some studies suggest that the Amazon rainforest, often called the lungs of the planet, is already there.

Using data dating back to 1990, the researchers analyzed manual measurements of tree species, size, and mass in 95 percent of the world’s forests to calculate how much carbon was stored over three decades. For each biome studied—temperate, boreal, and tropical forests—the researchers looked at how long-term landscape changes altered the region’s capacity to absorb emissions.

In the boreal forest, the world’s largest terrestrial biome that spans the upper northern hemisphere, researchers found a dire situation. Over the study period, these sensitive tree species lost 36 percent of their ability to absorb carbon as logging, wildfires, pests and drought devastated the land.

Some regions are worse off than others: In Canada, wildfires have turned boreal forests into a source of carbon emissions. In forests in Asian Russia, similar conditions have caused the region to lose 42% of its resistance to subsidence.

It’s the clear consequence of decades of increasingly frequent fires. A study published in Nature in June, which examined 21 years of satellite records, was the first to confirm that the frequency and magnitude of extreme fires has more than doubled worldwide. The change is particularly dramatic in boreal forests, where such fires have become more than 600% more frequent per year.

“I was just shocked by the scale of the disaster,” said Calum Cunningham, a postdoctoral researcher at the University of Tasmania and lead author of the wildfire study.

Near the equator, where tropical forests account for more than half of the world’s forested area, the Global Carbon Sequestration Study found a complex three-part equation. Agricultural deforestation led to a 31 percent loss of old-growth forest’s ability to absorb carbon. But new plant life took over vast swathes of abandoned farmland, and the carbon-absorbing capacity of these young forests offset losses from logging. Although continued deforestation continues to create more emissions, the study found that when these gains and losses are added together, tropical forests are nearly carbon neutral.

How has the planet managed to maintain this balance? The answer lies in temperate forests, where the carbon sink has increased by 30%. The study found that decades of reforestation efforts, mostly through national programs in China, are finally paying off. But this trend may not last. In China, urbanization and logging have begun to reduce forest cover. In the United States and Europe, wildfires, droughts, and pests have caused the carbon sink of temperate forests to decline by 10% and 12%, respectively.

Forest management efforts, as well as the rate of emissions, will determine how things play out. A paper in Nature last year reported “striking uncertainty” about the carbon storage potential of U.S. forests, underscoring the need for conservation and restoration efforts.

Chao Wu, a postdoctoral researcher at the University of Utah who led the 2023 study, said reducing emissions should be the top priority in solving the climate crisis. “But the other big piece is looking at nature-based climate solutions, and forests are going to be a really big part of that,” Wu said.

Richard Houghton, a senior scientist at the Woodwell Climate Research Center, a nonprofit that contributed to the latest sequestration study, says it’s “kind of a matter of luck” that the global forest carbon sink has remained stable.

To keep it that way, Houghton and Pan said, we need to step up restoration efforts and reduce logging in all biomes, especially in tropical forests, where 95 percent of deforestation occurs. “We’re not doing enough conservation,” Houghton said, adding that protecting forests has benefits for biodiversity and ecosystem health. “There’s always more reason to do a better job.”

This article was originally published in Grist at https://grist.org/science/forests-global-carbon-sink-study/.

Grist is an independent, nonprofit media organization dedicated to telling stories of climate solutions and a just future. Learn more at Grist.org

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This story was originally published by Grist.

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