What if we stopped cutting down forests to produce palm oil and cattle? What if we grew new forests on vacant city lots, old industrial buildings — even golf courses?
For the first time, scientists have sought to quantify this thought experiment. How many trees could be planted on every available parcel of land on Earth, where they could go, and what impact could that have on our survival?
They concluded that the planet could support nearly 2.5 billion additional acres of forest without shrinking our cities and farms, and that those additional trees, when they mature, could store a whole lot of the extra carbon — 200 gigatons of carbon, to be precise — generated by industrial activity over the last 150 years.
Parts of the study — led by researchers at ETH Zurich, a university that specializes in science, technology and engineering — were immediately criticized.
The critics did not dispute that 200 gigatons of carbon could be absorbed by trees if you planted them on every space of land available. They disputed the implications.
The study’s authors asserted that, under their model, forest restoration could absorb two-thirds of historic emissions. Zeke Hausfather, an analyst for the climate science website Carbon Brief, said the true figure would be closer to one-third. That’s because part of the emissions absorbed by the additional trees would have been absorbed by the soil or the seas anyway.