At COP28, ecologist Thomas Crowther, former chief scientific adviser for the United Nations’ Trillion Trees Campaign, was doing something he never would have expected a few years ago: begging environmental ministers to stop planting so many trees. Mass plantations are not the environmental solution they’re purported to be, Crowther argued. The potential of newly created forests to draw down carbon is often overstated. They can be harmful to biodiversity. Above all, they are really damaging when used as avoidance offsets— “as an excuse to avoid cutting emissions,” Crowther said. …In 2019, his lab at ETH Zurich found that the Earth had room for an additional 1.2 trillion trees, which could suck down as much as two-thirds of the carbon that humans have emitted. …Crowther, who says his message was misinterpreted, put out a more nuanced paper last month, which shows that preserving existing forests can have a greater climate impact than planting trees.