Estimating the Thermodynamic Contribution to Recent Greenland Ice Sheet Surface Mass Loss

Abstract. The Greenland Ice Sheet has become the largest single frozen source of global sea level rise following a pronounced increase in meltwater runoff in recent decades. The pivotal role of anomalous anticyclonic circulation patterns in facilitating this increase has been widely documented; however, this change in atmospheric circulation has coincided with a rapidly warming Arctic. While amplified warming at high latitudes has undoubtedly contributed to trends in Greenland's mass loss, the contribution of this shift in background conditions relative to changes in regional circulation patterns has yet to be quantified. Here, we apply the pseudo-global warming method of dynamical downscaling to estimate the contribution of the change in the thermodynamic background state under global warming to observed Greenland Ice Sheet surface mass loss since the turn of the century. Our analysis demonstrates that, had the recent atmospheric dynamical forcing of the Greenland Ice Sheet occurred under a preindustrial setting, anomalous surface mass loss would have been reduced by over 62 % relative to observations. We show that the change in the thermodynamic environment under amplified Arctic warming has augmented melt of the ice sheet via longwave radiative effects accompanying an increase in atmospheric water vapor content. Furthermore, the thermodynamic contribution to surface mass loss over the exceptional melt years of 2012 and 2019 was less than half that of the long-term average, demonstrating a reduced influence during periods of strong synoptic-scale atmospheric forcing.