This is where the world could support new forests. The map excludes existing forests, urban areas, and agricultural lands.

The Red Tea Detox

J. Bastin, et. al., Science 365, 76, 2019

Global temperatures could rise 1.5° C above industrial levels by as early as 2030 if current trends continue, but trees could help stem this climate crisis. A new analysis finds that adding nearly 1 billion additional hectares of forest could remove two-thirds of the roughly 300 gigatons of carbon humans have added to the atmosphere since the 1800s. 

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

The latest report from the United Nations’s Intergovernmental Panel on Climate Change recommended adding 1 billion hectares of forests to help limit global warming to 1.5° C by 2050. Ecologists Jean-Francois Bastin and Tom Crowther of the Swiss Federal Institute of Technology in Zurich and their co-authors wanted to figure out whether today’s Earth could support that many extra trees, and where they might all go.

They analyzed nearly 80,000 satellite photographs for current forest coverage. The team then categorized the planet according to 10 soil and climate characteristics. This identified areas that were more or less suitable for different types of forest. After subtracting existing forests and areas dominated by agriculture or cities, they calculated how much of the planet could sprout trees.

Earth could naturally support 0.9 billion hectares of additional forest—an area the size of the United States—without impinging on existing urban or agricultural lands, the researchers report today in Science. Those added trees could sequester 205 gigatons of carbon in the coming decades, roughly five times the amount emitted globally in 2018. 

“This work captures the magnitude of what forests can do for us,” says ecologist Greg Asner of Arizona State University in Tempe, who was not involved in the research. “They need to play a role if humanity is going to achieve our climate mitigation goals.”

Adding forests wouldn’t just sequester carbon. Forests provide a host of added benefits including enhanced biodiversity, improved water quality, and reduced erosion. Estimates of how much forest restoration on this scale would cost vary, but based on prices of about $0.30 a tree, Crowther says it could be roughly $300 billion.

Exactly how much carbon future forests could store may not be crystal clear, but Duncanson says NASA has new instruments in space—like the Global Ecosystem Dynamics Investigation (GEDI) aboard the International Space Station—that will use lasers to create high-resolution 3D maps of Earth’s forests from canopy to floor. These data will add much-needed precision to existing estimates of aboveground carbon storage. 

“With GEDI we can take this paper as a stepping stone and inform it with much more accurate carbon estimates,” Duncanson says. “There have always been large uncertainties on large-scale carbon totals, but we have richer data coming soon.”

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