Reforestation and afforestation (R&A) are well-established climate mitigation strategies in the wet tropics due to high carbon sequestration rates of forests/trees. However, at high latitudes (boreal regions), the low albedo of trees–compared to snow and other lighter land surfaces–leads to the absorption of energy, thus creating a warming effect that has a greater impact on temperature than the carbon capture accomplished by the limited vegetation productivity in boreal regions. This study explores the balance between albedo and carbon sequestration of forests at mid-latitudes, which has been less clear.
The authors found that forested areas have greater cloud cover than other types of land cover at midlatitudes, resulting in a higher albedo at the top of the atmosphere–where the clouds are–and leading to greater cooling. Specifically, they found “an association of forested lands with increased cloudiness… As a result, forests reflect extra solar radiation and thus reduce the radiative impacts of the lower surface albedo. This in turn implies a cooling effect of R&A at midlatitudes” [Cerasoli 2021: 1-2]. The increase in cloudiness is due to earlier afternoon cloud formation over forests compared to other vegetation types in wet regions.
Our results provide substantial evidence of remarkable benefits of R&A [reforestation and afforestation] around the 30° to 45° latitudinal range, due to the combined benefits of biomass gain and promotion of cloud formation over forests [Cerasoli 2021: 4].
Cerasoli, Sara, Jun Yin & Amilcare Porporato, 2021, Cloud cooling effects of afforestation and reforestation at midlatitudes, PNAS 118(33), https://www.pnas.org/content/118/33/e2026241118.