Accounting for albedo change to identify climate-positive tree cover restoration

Restoring tree cover changes surface albedo, often reducing the fraction of sunlight reflected and causing warming that can offset or negate carbon removal benefits. Previous global assessments of tree cover restoration benefits have not robustly accounted for spatially explicit albedo effects. Here we produce global maps that convert albedo change to carbon dioxide equivalents (CO2e) using radiative kernels, showing that carbon-only estimates can be up to 81% too high. Dryland and boreal regions show especially strong albedo offsets, though climate-positive opportunities exist in all biomes. We further find that on-the-ground projects tend to occur in more climate-positive locations, but most still face at least a 20% albedo offset. Accounting for albedo change is therefore essential to strategically deploy tree cover restoration for maximum climate benefit, and we provide tools and datasets to enable such accounting. The climate warming response to surface albedo change can be directly compared with changes in carbon storage by expressing both in CO2e. We convert surface albedo changes to top-of-atmosphere radiative forcing (TOA RF) using the radiative kernel technique, and then to CO2e by finding the equivalent CO2 pulse that yields the same TOA RF after accounting for CO2 decay over 100 years via an impulse response function. Expressing both processes in CO2e allows calculation of the percentage of carbon storage cooling that is offset by albedo-induced warming (“albedo offset”): 50% indicates halving of the net climate benefit, and >100% indicates a net climate-negative outcome. Although restoring tree cover also alters clouds, evaporation, sensible heat, and other factors, their net global impacts are not yet tractable, and in some locations albedo dominates other factors.

Natalia Hasler, Christopher A. Williams, Vanessa Carrasco Denney, Peter W. Ellis, Surendra Shrestha, Drew E. Terasaki Hart, Nicholas H. Wolff, Samantha Yeo, Thomas W. Crowther, Leland K. Werden, Susan C. Cook-Patton