Electric vehicles. Carbon-capture devices. Replacing cattle with bison. Lots of ideas have been tossed around for addressing climate change, but a new study suggests that one of the most effective solutions is pretty simple: Just plant more trees—a trillion of them to be exact.
The research, conducted by the Swiss university ETH Zurich, found that around 0.9 billion hectares (roughly 2.2 billion acres) of land is suitable for reforestation around the globe. If it were populated with trees, they could capture about 205 billion metric tons of carbon: That’s two-thirds of all the human-generated carbon emissions released since the Industrial Revolution.
“We all knew that restoring forests could play a part in tackling climate change, but we didn’t really know how big the impact would be,” professor and study co-author Thomas Crowther said in a press release. “Our study shows clearly that forest restoration is the best climate change solution available today.”
Trees are a natural defense. As they grow, they pull carbon out of the air through photosynthesis. That makes reforestation an especially enticing strategy for counteracting emissions, since there’s no expensive technology required—just water, soil, and sunlight.
To estimate the amount of possible tree cover, the ETF Zurich researchers first calculated how much forested land the planet could support under current climate conditions. To do so, they assessed tens of thousands of high-resolution satellite images to measure existing forests, The Guardian reports. Then they combined that data with information on soil types, topography, and climate to create a map of potential tree cover.
The map showed about 4.4 billion hectares of potential forest—a significant increase from the 2.8 billion hectares of forest currently spread across the earth. Then, Crowther and his team subtracted the areas that couldn’t support trees because they’re occupied by cities or farms. They included grazing land, since some trees on the pasture wouldn’t interfere with livestock, according to The Guardian. That left 0.9 billion hectares of land—an area slightly larger than the United States—not used by humans that would be suitable for trees.
Six countries stand out as the best candidates for reforestation, according to the study. The first is Russia, which has 151 million hectares of suitable land for forests; followed by the United States, with 103 million hectares; Canada, Australia, Brazil, and China round out the list.
What’s more, the authors refute the idea that a warming planet will increase forest cover. Their data shows that higher temperatures might enlarge forests in the northern latitudes, but the gains will be offset by losses in the dense tropical rainforests, which could become too hot to be habitable.
Although reforestation seems like a no-brainer, the study addresses a key gap in understanding how it would work as a climate-change strategy. Before the study, it wasn’t clear how many trees could be planted without encroaching on human living space or food production, and what effect the plants would have. It’s valuable information for organizations looking for effective ways to fight climate change.
“This is a hugely important blueprint for governments and private sector,” Christina Figueres, former UN climate chief, told The Guardian.
Not all the experts are convinced by the study’s numbers, however. Zeke Hausfather, an analyst at Carbon Brief, told The New York Times that the proposed reforestation would likely only capture about one-third of carbon emissions. Even so, he and other experts agreed that planting trees should be included in any comprehensive climate action plan.
In Crowther’s view, growing forests represents the cheapest and most viable strategy for dealing with carbon emissions. It’s also a way for everyone to help, either by planting trees themselves or donating to forest restoration initiatives.
“But we must act quickly, as new forests will take decades to mature and achieve their full potential as a source of natural carbon storage,” he said.