The influence of North Atlantic atmospheric and oceanic forcing effects on 1900–2010 Greenland summer climate and ice melt/runoff

Abstract

Correlation analysis of Greenland coastal weather station temperatures against the North Atlantic Oscillation (NAO) and the Atlantic Multidecadal Oscillation (AMO) indices for the summer season (when Ice Sheet melt and runoff occur) reveals significant temporal variations over the last 100 years, with periods of strongest correlations in the early twentieth century and during recent decades. During the mid-twentieth century, temperature changes at the stations are not significantly correlated with these circulation indices. Greenland coastal summer temperatures and Greenland Ice Sheet (GrIS) runoff since the 1970s are more strongly correlated with the Greenland Blocking Index (GBI) than with the NAO Index (NAOI), making the GBI a potentially useful predictor of ice-sheet mass balance changes. Our results show that the changing strength of NAOI-temperature relationships found in boreal winter also extends to summer over Greenland. Greenland temperatures and GrIS runoff over the last 30-40 years are significantly correlated with AMO variations, although they are more strongly correlated with GBI changes. GrIS melt extent is less significantly correlated with atmospheric and oceanic index changes than runoff, which we attribute to the latter being a more quantitative index of Ice Sheet response to climate change. Moreover, the four recent warm summers of 2007-2010 are characterised by unprecedented high pressure (since at least 1948 -the start of the NCEP/NCAR reanalysis record) in the tropospheric column. Our results suggest complex and changing atmospheric forcing conditions that are not well captured using the NAO alone, and support theories of an oceanic influence on the recent increases in Greenland temperatures and GrIS runoff.

On the recent contribution of the Greenland ice sheet to sea level change

“…Examples of important processes that are poorly or not at all represented in current models are interactive snow/ice darkening by future enhanced dust/black carbon deposition or microbiological processes (Stibal et al, 2012), and sub-, supra-and englacial hydrology, including vertical and horizontal flow of meltwater in firn or over ice lenses (De la Peña et al, 2015;Machguth et al, 2016). Other emerging research topics of GrIS melt climate are the impact of atmospheric circulation changes on Greenland melt (Hanna et al, 2013a(Hanna et al, , 2014McLeod and Mote, 2016;Tedesco et al, 2013), the impact of rain on ice sheet motion (Doyle et al, 2015), the effect of liquid water clouds on the surface energy balance and melt (Bennartz et al, 2013;Van Tricht et al, 2016) and the increased role of turbulent heat exchange during strong melting episodes over the margins of the GrIS . Finally, it is desirable that, once developed and tested, a single, sophisticated snow model is used to simulate both the deep firn layer over the ice sheet and the seasonal snow cover over the tundra.…”

“…for large-scale atmospheric drivers Hanna et al, 2013aHanna et al, , 2014Hanna et al, , 2016McLeod and Mote, 2016) and local feedback processes. Especially important is the albedo-melt feedback , which constitutes the darkening of snow once it has melted, as well as the lengthening of the exposure of dark, bare ice in the ablation zone once the winter snow has melted away (Tedesco et al, 2011).…”

Drivers and potential predictability of summer time North Atlantic polar front jet variability

“…The strong cold stratospheric polar vortex will reduce the likelihood of cold air outbreaks over the eastern United States while a warm, weaker vortex will increase this possibility, and is therefore associated with high snow anomalies. However, low (high) February snow anomaly years are associated with prolonged periods with relatively low (high) values of the Greenland Blocking Index in August (GBI;Fang 2004;Hanna et al 2013), favouring a positive (negative) SNAO (Fig. 12d).…”

Exceptional summer warming leads to contrasting outcomes for methane cycling in small Arctic lakes of Greenland

“…As a result of amplified warming in the Arctic over the past 20 years (IPCC, 2013), Greenland has experienced significant mass loss of the Greenland Ice Sheet (GIS; Nghiem et al, 2012;van As et al, 2012;Hall et al, 2013;Hanna et al, 2013Hanna et al, , 2014. Despite the abundance of lakes on the ice-free margin of Greenland and intense changes to the landscape as the result of warming, there are only a few published studies that have measured CH 4 in Greenlandic lakes (Walter Anthony et al, 2012;Webster et al, 2015;Cadieux et al, 2016;Goldman et al, 2016).…”