Radiative forcing reduced by early twenty-first century increase in land albedo.

Surface albedo greatly affects how much energy the Earth absorbs. Intensive human activities and accelerated climate change have altered surface albedo across spatial and temporal scales, yet assessments of the effects of land use or land cover (LULC) and snow variations on land surface albedo are scarce at the global scale. As a result, the global land surface albedo dynamics over recent decades and their corresponding radiative forcing to the climate system remain poorly understood. Here we quantify the individual and combined effects of snow cover dynamics, LULC conversions and non-conversion regions on albedo variations during 2001-2020 and estimate their induced radiative forcing. We show that the negative radiative forcing induced by the global land surface albedo change was -0.142 (-0.158, -0.114) W m over the past two decades. The global snow-free land surface albedo increased by 2.2% (P < 0.001), with a negative radiative forcing of -0.164 (-0.186, -0.138) W m (P < 0.001). The magnitude of this negative forcing is sevenfold larger than the positive forcing induced by snow dynamics, and equivalent to 59.9% of that caused by CO emissions from 2011 to 2019. The global radiative forcing due to albedo changes in LULC non-conversion regions is 3.9 to 8.1 times greater than that from LULC conversions. The radiative forcing induced by albedo changes highlights the important role of land surface dynamics in modulating global warming.