Recent strengthening of snow and ice albedo feedback driven by Antarctic sea-ice loss

The decline of the Arctic cryosphere during recent decades has lowered the region's surface albedo, reducing its ability to reflect solar radiation back to space. It is not clear what role the Antarctic cryosphere plays in this regard, but new remote-sensing-based techniques and datasets have recently opened the possibility to investigate its role. Here, we leverage these to show that the surface albedo reductions from sustained post-2000 losses in Arctic snow and ice cover equate to increasingly positive snow and ice albedo feedback relative to a 1982-1991 baseline period, with a decadal trend of +0.08 ± 0.04 W m^-2 decade^-1 between 1992 and 2015. During the same period, the expansion of the Antarctic sea-ice pack generated a negative feedback, with a decadal trend of −0.06 ± 0.02 W m^-2 decade^-1. However, substantial Antarctic sea-ice losses during 2016-2018 completely reversed the trend, increasing the three-year mean combined Arctic and Antarctic snow and ice albedo feedback to +0.26 ± 0.15 W m^-2. This reversal highlights the importance of Antarctic sea-ice loss to the global snow and ice albedo feedback. The 1992-2018 mean feedback is equivalent to approximately 10% of anthropogenic CO₂ emissions over the same period; the share may rise markedly should 2016-2018 snow and ice conditions become common, although increasing long-wave emissions will probably mediate the impact on the total radiative-energy budget.