Spatial Variability in the Albedo-Derived Warming Effect of Afforestation

The IPCC’s 2018 special report emphasizes the necessity of large-scale biological carbon sequestration, in addition to rapid emissions reductions, to restrain global warming to 1.5 ֯ Celsius. While afforestation is a popular, scalable, and cost-effective biosequestration strategy, it also reduces the earth’s overall shortwave albedo. The magnitude of afforestation’s albedo-warming effect varies by location, potentially offsetting some or all of the cooling from CO2 sequestration (several earth system model experiments have indicated that high-latitude afforestation could even lead to accelerated global warming). Most proposed carbon accounting schemes do not account for these spatially variable albedo effects, thereby running the risk of significantly overestimating the global cooling potential of afforestation, and incentivizing ineffective boreal afforestation efforts. Using global snow cover, irradiance, and land surface data derived from NASA and NOAA radiometric sensing, we map the estimated albedo-derived radiative forcing potential of a hypothetical shift from degraded cropland to forest plantations across the earth’s surface. These values are then time-integrated to 2050 and converted to equivalent CO2 emissions. Finally, using ArcMap’s zonal statistics tool, in conjunction with regional carbon sequestration rates, we produce a table of “albedo takeback” coefficients for afforestation’s 2050 cooling effect across different climate zones. These results can be integrated into carbon accounting schemes to account for the global warming effect of albedo reduction from afforestation.