As countries and companies pour money into planting trees as part of the fight against climate change, there’s another way to regrow forests that gets less attention: when humans simply get out of the way and do nothing, the process can also happen naturally on land that has been deforested. The potential for natural forest regrowth globally could capture as much as 8.9 billion metric tons of carbon dioxide every year, the equivalent of a quarter of the world’s human-made emissions.
The numbers come from a study, published in Nature, that maps out the carbon-capturing potential of these forests around the world in detail. How much carbon each forest can store varies by as much as 100 times depending on the location. Before the study, there was only limited data from particular places. “We developed a machine learning model that could take the information from those different plots, and predict other places like that where these same forest regrowth rates are likely to apply,” says Nancy Harris, a research manager at Global Forest Watch at the World Resources Institute, a nonprofit that worked with the Nature Conservancy and other organizations on the study.
In some cases, the potential for these forests to store carbon was greater than researchers previously thought—the numbers that countries have been using for tropical forests, for example, underestimated their carbon storage by 50%. The new map could help countries better plan for the future by helping identify areas to prioritize for this type of work. “It can help people figure out where there might be the most carbon benefit or carbon reward for letting forests regrow,” says David Gibbs, a GIS research associate at World Resources Institute.