New estimate of the carbon-capturing potential of forests is substantial, but some scientists say it’s not realistic.
The restoration and protection of forests worldwide could help remove about 226 gigatons of carbon from the atmosphere, according to a study published today in Nature. That’s equivalent to roughly 20 years of emissions from burning fossil fuels and other sources at current rates. Some experts say the analysis provides a more reliable estimate of the carbon-capturing potential of forests than a previous, controversial study that analyzed only the potential benefit from restoring trees to degraded land. But critics are skeptical that the new number is even remotely achievable.
The findings provide “clarity and confidence around the substantive role” of forests in fighting the climate crisis, says Wayne Walker, chief scientific officer of the Woodwell Climate Research Center, who was not involved in the research. Although there’s still “much uncertainty” as to the exact amount of additional carbon that forests could take up, Walker says the evidence is strong enough to justify acting to plant, restore, and protect forests.
But Joseph Veldman, an ecologist and conservation biologist at Texas A&M University, isn’t convinced by the numbers. “This new study has many serious problems,” he says. For instance, much of the carbon benefit would come from planting trees in grasslands and other areas where they don’t belong, Veldman says, which threatens biodiversity in these ecosystems.
Humans have cut down a significant fraction—perhaps as much as half—of the forests that once existed. And every year, deforestation contributes 15% of all the greenhouse gas emissions caused by humans. So, scientists have been interested in finding out how much carbon trees could take out of the atmosphere if forests are allowed to regrow.
In 2019, a group led by ecologist Thomas Crowther of ETH Zürich published a paper in Science estimating that 205 gigatons of carbon could be taken up if forests were restored across 0.9 billion hectares of land, an area that’s roughly 10 times the size of China. Other scientists criticized the study, saying the figure was much too high because it assumed that each hectare of forest would capture and store 227 tons of carbon. The 227 tons was “an absurd figure,” says Simon Lewis, a global change scientist at University College London and the University of Leeds who wrote a critique of the 2019 paper. Some also worried the study would encourage climate mitigation efforts such as the planting of large tree plantations, which aren’t as beneficial for biodiversity and carbon capture as natural and diverse forests.
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