Abstract for: Climate impacts of afforestation and forest restoration

Limiting global warming to “well below 2°C” as agreed in the Paris Climate Accords requires greenhouse gas (GHG) emissions fall rapidly and reach net zero by approximately 2050. However, many IPCC net zero scenarios assume fossil fuel use cannot fall fast enough to do so, thus requiring significant “negative emissions” including afforestation and forest restoration, and many nations and firms rely on forestry policies to meet their net-zero commitments. Here we assess the potential of afforestation and forest restoration to reduce GHG emissions in time to avoid the worst harms from climate change. We use the En-ROADS climate policy model to simulate the dynamics of afforestation and forest restoration, including delays in program implementation and how quickly tree growth can remove carbon from the atmosphere. Under optimistic assumptions we find aggressive restoration and afforestation programs would not delay when the 1.5 and 2°C thresholds are breached and yield a small reduction in mean global temperature by 2100: 0.08 to 0.20°C. The results are robust to critical uncertainties. This is because land use comprises a small fraction of total GHG emissions and achieving the carbon sequestration potential of afforestation and restoration requires well over a century. Forest preservation and restoration are vital to protect indigenous communities, biodiversity, water availability, and other critical ecosystem services. But forest restoration and afforestation are not silver bullets to solve the climate crisis and cannot substitute for rapid, deep cuts in fossil fuel emissions.