Interactions between Increasing CO2 and Antarctic Melt Rates

Abstract

Meltwater from the Antarctic ice sheet is expected to increase the sea ice extent. However, such an expansion may be moderated by sea ice decline associated with global warming. Here we investigate the relative balance of these two processes through experiments using HadGEM3-GC3.1 and compare these to two standard idealized CMIP6 experiments. Our results show that the decline in sea ice projected under scenarios of increasing CO2 may be inhibited by simultaneously increasing melt fluxes. We find that Antarctic Bottom Water formation, projected to decline as CO2 increases, is likely to decline further with an increasing meltwater flux. In our simulations, the response of the westerly wind jet to increasing CO2 is enhanced when the meltwater flux increases, resulting in a stronger peak wind stress than is found when either CO2 or melt rates increase exclusively. We find that the sensitivity of the Antarctic Circumpolar Current to increasing melt fluxes in the Southern Ocean is countered by increasing CO2, removing or reducing a feedback mechanism that may otherwise allow more heat to be transported to the polar regions and drive increasing ice shelf melt rates. The insights presented here and in a companion paper (which focuses on the effect of increasing melt fluxes under preindustrial forcings) provide insights helpful to the interpretation of both future climate projections and sensitivity studies into the effect of increasing melt fluxes from the Antarctic ice sheet when different forcing scenarios are used.