Historical and future roles of internal atmospheric variability in modulating summertime Greenland ice sheet melt

Understanding how internal atmospheric variability affects Greenland ice sheet (GrIS) summertime melting would improve understanding of future sea level rise. We analyze the Community Earth System Model Large Ensemble (CESM-LE) over 1951-2000 and 2051-2100. We find that internal variability dominates the forced response on short timescales (similar to 20 years) and that the area impacted by internal variability grows in the future, connecting internal variability and climate change. Unlike prior studies, we do not assume specific patterns of internal variability to affect GrIS melting but derive them from maximum covariance analysis. We find that the North Atlantic Oscillation (NAO) is the major source of internal atmospheric variability associated with GrIS melt conditions in CESM-LE and reanalysis, with the positive phase (NAO+) linked to widespread cooling over the ice sheet. CESM-LE and CMIP5 project an increase in the frequency of NAO+ events, suggesting a negative feedback to the GrIS under future climate change.