Greenland Ice Sheet Rainfall, Heat and Albedo Feedback Impacts From the Mid‐August 2021 Atmospheric River

Abstract

Rainfall at the Greenland ice sheet Summit 14 August 2021, was delivered by an atmospheric river (AR). Extreme surface ablation expanded the all‐Greenland bare ice area to near‐record‐high with snowline climbing up to 788 ± 90 m. Ice sheet wet snow extent reached 46%, a record high for the 15–31 August AMSR data since 2003. Heat‐driven firn deflation averaged 0.14 ± 0.05 m at four accumulation area automatic weather stations (AWSs). Energy budget calculations from AWS data indicate that surface heating from rainfall is much smaller than from either the sensible, latent, net‐longwave or solar energy fluxes. Sensitivity tests show that without the heat‐driven snow‐darkening, melt at 1,840 m would have totaled 28% less. Similarly, at 1,270 m elevation, without the bare ice exposure, melting would have been 51% less. Proglacial river discharge was the highest on record since 2006 for late August and confirms the melt‐sustaining effect of the albedo feedback.

State of the Climate in 2021

“…(This chapter includes a focus on glaciers and ice caps outside Greenland, section 5f, which alternates yearly with a section on Arctic river discharge, as the scales of regular observation for both of these climate components are best suited for reporting every two years.) (Box et al 2019). Warming has been linked with changing frequency, intensity, and duration of high-latitude atmospheric extremes that impact snow and ice melt (Walsh et al 2020).…”

“…5.12b) and albedo anomalies (Fig. 5.13a) may not intuitively align due to factors such as summer snowfall, surface atmospheric conditions, and extreme melt events (e.g., Box et al 2022).…”

“…5.15). While their potential longerterm contribution to sea level rise is small compared to the ice sheets, they are sensitive to changes in climate and have been a large contributor to recent sea level rise in response to continued atmospheric warming (Ciracì et al 2020;Millan et al 2017;Wouters et al 2019). Recent increases in global temperature, amplified at high northern latitudes (section 5b, Fig.…”

“…Because some of these data are still provisional, we provide added context to recent changes in pan-Arctic glacier mass balance by also reporting on the 24 glaciers measured in the previous mass balance year of 2019/20 (World Glacier Monitoring Service [https://wgms.ch/] 2021; Kjøllmoen et al 2021). These glaciers are located in Alaska (three), Arctic Canada (four), Iceland (nine), Svalbard (three), Norway (two), and Sweden (three; Surface mass balance and overall state-of-health of Arctic glaciers and ice caps is closely linked with summer warmth (Box et al 2019). Strongly negative values of B clim for glaciers and ice caps across Svalbard in the 2019/20 balance year were associated with summer (June-August, JJA) atmospheric temperature (925 hPa; NCEP/NCAR) anomalies 2.5° to 3°C above the 1981-2010 mean (Ballinger et al 2020).…”

The Arctic

“…5.15). While their potential longerterm contribution to sea level rise is small compared to the ice sheets, they are sensitive to changes in climate and have been a large contributor to recent sea level rise in response to continued atmospheric warming (Ciracì et al 2020;Hugonnet et al 2021;Millan et al 2017;Wouters et al 2019). Recent increases in global temperature, amplified at high northern latitudes (section 5b, Fig.…”