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A 2018 report by the Intergovernmental Panel on Climate Change said that curbing global warming would require planting 1 billion hectares of additional forest. That’s a forest about the size of the United States. It may sound daunting, but according to a study published today (July 5) in Science, the planet essentially has room for the extra trees.

Not counting agricultural areas, cities, and existing forests, the globe can accommodate an additional 0.9 billion hectares of forest, the study found. That much forest area, if allowed to mature, could result in the storage of an estimated 205 gigatons of carbon, or about two-thirds of the carbon that humans have added to the atmosphere since the 1800s.

“This is by far—by thousands of times—the cheapest climate change solution,” Thomas Crowther, who led the study, tells the Associated Press, adding that it’s also the most effective solution available.

“Forests represent one of our biggest natural allies against climate change,” Laura Duncanson, a carbon storage researcher at the University of Maryland, College Park, and NASA who was not involved in the research, tells Science, adding that “this is an admittedly simplified analysis of the carbon restored forests might capture, and we shouldn’t take it as gospel.”

The Intergovernmental Panel on Climate Change’s (IPCC) special report suggested that planting 1 billion hectares of trees would be necessary to prevent global temperatures from increasing by 1.5 degrees Celsius by 2050, so Crowther and Jean-Francois Bastin, ecologists at Switzerland’s ETH-Zurich, and colleagues decided to explore whether that was theoretically possible. They analyzed about 80,000 satellite photos to identify areas that could support different types of forests. They then subtracted existing forests, agricultural areas, and urban areas to determine how much land remained for forestation.

The 0.9 billion hectares of additional forest would translate to 1–1.5 trillion trees, adding to the 3 trillion trees on Earth already, the AP reports. More than half the restoration potential lies in six countries alone: Russia, the US, Canada, Australia, Brazil, and China.

The results indicate that the IPCC target for forest restoration is “undoubtedly achievable under the current climate,” the authors write in their paper.

But the current climate is changing, so humans will have to act fast to take advantage of this potential solution. If the globe stays on its current warming trajectory, the study authors note, the area available for new forests will shrink by 223 million hectares, or nearly a quarter, by 2050.

Ashley P. Taylor is a New York–based freelance journalist. Find her on Twitter @crenshawseeds.