The appeal of reforestation is almost intuitive. Trees absorb carbon dioxide. The planet has too much carbon dioxide. Plant more trees, fix the problem. It is the kind of logic that has fuelled commitments from governments, corporations, and international bodies to plant billions, even trillions, of trees in the coming decades. The science, it turns out, is considerably more complicated than that. New research from ETH Zurich, finds that the location of reforestation matters as much as the scale, and in some cases more. Two scenarios differing by 450 million hectares, an area roughly the size of all European Union countries combined, can produce nearly identical cooling effects by the end of the century. Meanwhile, planting forests in the wrong places can actually warm the climate. In some cases, the warming partially or even fully cancels out the carbon benefits. “The fact that we can achieve the same cooling effect with significantly less land shows that where we plant is more important than how much we plant,” said Nora Fahrenbach, a doctoral student at ETH …