Abstract for: Assessing the dynamic impact of afforestation on climate change

Afforestation is widely promoted to help achieve net-zero emissions and keep global warming well below 2°C. Afforestation is important in many IPCC net-zero scenarios, the net-zero pledges of nations and firms, and the voluntary carbon market. Its proponents argue that afforestation can limit warming significantly. Others, however, question the climate mitigation impact of afforestation because of its competition for land with food production, its realistic potential for carbon sequestration, and its negative impact on albedo, diminishing its cooling benefits. Here we explore an aspect of afforestation’s climate mitigation potential that is often overlooked: how the dynamics of forest growth affect its impact. We use the En-ROADS climate policy model and growth curves for 51 forest types. We find that under optimistic assumptions for land availability, forest carbon density, and carbon loss rates, afforestation yields a reduction in mean global surface temperature by 2100 of only about 0.2°C under the most favorable conditions. While it may be valuable, especially if done in ways that support biodiversity and other ecosystem services, afforestation is not a high-leverage climate solution, cannot substitute for rapid, deep cuts in fossil fuel emissions, and should not be used for offsets that justify further emissions.