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

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 scales1,2,3, 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 understood4,5,6,7,8,9. 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−2 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−2 (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 CO2 emissions from 2011 to 201910. 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. Grant no. NA19NES4320002

地表反照率（Surface albedo）极大地影响地球吸收的能量总量。高强度人类活动与加速演进的气候变化已在各类时空尺度上改变了地表反照率¹,²,³，但当前全球尺度下针对土地利用/土地覆被（Land Use/Land Cover, LULC）与积雪变化对地表反照率影响的评估研究仍较为匮乏。因此，近数十年来全球地表反照率的动态变化及其对气候系统的辐射强迫效应，至今仍未得到充分认知⁴,⁵,⁶,⁷,⁸,⁹。本研究量化了2001—2020年间积雪覆盖动态、LULC转换区与非转换区对反照率变化的单独及联合效应，并估算了由此引发的辐射强迫。研究结果显示，过去二十年间全球地表反照率变化所导致的负辐射强迫为-0.142（95%置信区间：-0.158~-0.114）W·m⁻²。全球无积雪地表反照率上升了2.2%（P<0.001），对应的负辐射强迫为-0.164（95%置信区间：-0.186~-0.138）W·m⁻²（P<0.001）。该负辐射强迫的强度是积雪动态所引发正辐射强迫的7倍，相当于2011—2019年间二氧化碳排放所产生辐射强迫的59.9%¹⁰。LULC非转换区反照率变化引发的全球辐射强迫，是LULC转换区的3.9至8.1倍。反照率变化引发的辐射强迫，凸显了地表动态过程在调节全球变暖中的关键作用。资助项目编号：NA19NES4320002