Brief communication: Impact of the recent atmospheric circulation change in summer on the future surface mass balance of the Greenland Ice Sheet

Abstract

Abstract. Since the 2000s, a change in the atmospheric circulation over the North Atlantic resulting in more frequent blocking events has favoured warmer and sunnier weather conditions over the Greenland Ice Sheet (GrIS) in summer, enhancing the melt increase. This circulation change is not represented by general circulation models (GCMs) of the Coupled Model Intercomparison Project Phase 5 (CMIP5), which do not predict any circulation change for the next century over the North Atlantic. The goal of this study is to evaluate the impact of an atmospheric circulation change (as currently observed) on projections of the future GrIS surface mass balance (SMB). We compare GrIS SMB estimates simulated by the regional climate model MAR forced by perturbed reanalysis (ERA-Interim with a temperature correction of +1, +1.5, and +2 ∘C at the MAR lateral boundaries) over 1980–2016 to projections of the future GrIS SMB from MAR simulations forced by three GCMs over selected periods for which a similar temperature increase of +1, +1.5, and +2 ∘C is projected by the GCMs in comparison to 1980–1999. Mean SMB anomalies produced with perturbed reanalysis over the climatologically stable period 1980–1999 are similar to those produced with MAR forced by GCMs over future periods characterised by a similar warming over Greenland. However, over the 2 last decades (2000–2016) when an increase in the frequency of blocking events has been observed in summer, MAR forced by perturbed reanalysis suggests that the SMB decrease could be amplified by a factor of 2 if such atmospheric conditions persist compared to projections forced by GCMs for the same temperature increase but without any circulation change.

Unprecedented atmospheric conditions (1948–2019) drive the 2019 exceptional melting season over the Greenland ice sheet

“…Outputs generated at sub-daily temporal resolution are, then, aver-aged to obtain daily values. We refer to Fettweis et al (2017) for the evaluation of this NCEP/NCARv1 forced simulation and to Delhasse et al (2020) for the list of improvements made since MARv3.5 used in Fettweis et al (2017).…”

Importance of Orography for Greenland Cloud and Melt Response to Atmospheric Blocking

“…High pressure conditions are further linked to GrIS warming trends since the mid-1990s (Box et al 2012;Ding et al 2014;Fettweis et al 2013b) and record-breaking melt in recent summers (Hanna et al 2014;McLeod and Mote 2016;Tedesco et al 2013Tedesco et al , 2016. Having significantly increased since 1981 (Hanna et al 2016), summertime Greenland blocking is expected to remain an important driver of extreme melt throughout the twentyfirst century (Delhasse et al 2018;Hahn et al 2018;Hanna et al 2018;Hofer et al 2019). Predictions of Greenland melt therefore depend on understanding the impacts of blocking, with potential global effects on sea level rise (Aschwanden et al 2019;Fettweis et al 2013a;Shepherd et al 2012) and ocean circulation changes (Böning et al 2016;Oltmanns et al 2018;Rahmstorf et al 2015).…”

Likely and High-End Impacts of Regional Sea-Level Rise on the Shoreline Change of European Sandy Coasts Under a High Greenhouse Gas Emissions Scenario

“…Their highest Greenland SLE projection (0.17 m by 2100) was found when the ice-sheet model was forced by canESM2 RCP8.5 simulation results. However, using also a subset of CMIP5 models (including canESM2) and comparing with reanalysis, Delhasse et al (2018) [93] have shown that some changes observed over the last two decades in atmospheric circulation (i.e., increase in blocking high frequencies in summer) could not be reproduced by the CMIP5 models. They further concluded that, if the current summer atmospheric circulation pattern over Greenland happens to persist, projected Greenland SMB contribution to sea-level rise could be amplified by a factor of two for a similar temperature increase.…”

“…They further concluded that, if the current summer atmospheric circulation pattern over Greenland happens to persist, projected Greenland SMB contribution to sea-level rise could be amplified by a factor of two for a similar temperature increase. Therefore, we build our high-end B scenario by considering that the largest model projection found in Fürst et al (2015) [92] could be amplified by a factor two following the arguments of Delhasse et al (2018) [93]; this would lead to a Greenland SLE of 0.34 m by 2100. Note that the most recent expert elicitations on ice-sheet contribution suggested an upper bound of the likely range at 60 cm [73], which gives us confidence that our high-end B Greenland component projection remains credible.…”