Scientific American - July 4, 2019

We have heard for years that planting trees can help save the world from global warming. That mantra was mostly a statement of faith, however. Now the data finally exist to show that if the right species of trees are planted in the right soil types across the planet, the emerging forests could capture 205 gigatons of carbon dioxide in the next 40 to 100 years. That's two thirds of all the CO2 humans have generated since the industrial revolution. "Forest restoration is by far our most powerful planetary solution today," says Tom Crowther, a professor of global ecosystem ecology at the Swiss Federal Institute of Technology in Zurich, and an author of a study published Thursday in Science that generated the eye-opening number.

The study team analyzed almost 80,000 satellite photo measurements of tree cover worldwide and combined them with enormous global databases about soil and climate conditions, evaluating one hectare at a time. The exercise generated a detailed map of how many trees the earth could naturally support—where forests grow now and where they could grow, outside of areas such as deserts and savannahs that support very few or no trees. The team then subtracted existing forests and also urban areas and land used for agriculture. That left 0.9 billion hectares that could be forested but have not been. If those spaces were filled with trees that already flourish nearby, the new growth could store 205 gigatons of carbon by the time the forests mature.

After 40 to 100 years, of course, the storage rate would flatten as forest growth levels off—but the researchers say the 205 gigatons would be maintained as old trees die and new ones grow. There would be "a bank of excess carbon that is no longer in the atmosphere," Crowther says.

The team has also created a planning tool linked to the map that will be open to the public starting July 5. Individuals and organizations can zoom in to any location to see where new forests could be started. ...
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