Revealing the widespread potential of forests to increase low level cloud cover

Forests play a key role in humanity's current challenge to mitigate climate change thanks to their capacity to sequester carbon. Preserving and expanding forest cover is considered essential to enhance this carbon sink. However, changing the forest cover can further affect the climate system through biophysical effects. One such effect that is seldom studied is how afforestation can alter the cloud regime, which can potentially have repercussions on the hydrological cycle, the surface radiation budget and on planetary albedo itself. Here we provide a global scale assessment of this effect derived from satellite remote sensing observations. We show that for 67% of sampled areas across the world, afforestation would increase low level cloud cover, which should have a cooling effect on the planet. We further reveal a dependency of this effect on forest type, notably in Europe where needleleaf forests generate more clouds than broadleaf forests. Forests can influence climate by affecting low cloud formation, but where and when this occurs is not well known. Here, the authors provide a global-scale assessment, based on satellite remote sensing observations, suggesting afforestation mostly increases low cloud cover which could potentially cool surface temperatures.