Continental heat anomalies and the extreme melting of the Greenland ice surface in 2012 and 1889

Abstract

Recent decades have seen increased melting of the Greenland ice sheet. On 11 July 2012, nearly the entire surface of the ice sheet melted; such rare events last occurred in 1889 and, prior to that, during the Medieval Climate Anomaly. Studies of the 2012 event associated the presence of a thin, warm elevated liquid cloud layer with surface temperatures rising above the melting point at Summit Station, some 3212 m above sea level. Here we explore other potential factors in July 2012 associated with this unusual melting. These include (1) warm air originating from a record North American heat wave, (2) transitions in the Arctic Oscillation, (3) transport of water vapor via an Atmospheric River over the Atlantic to Greenland, and (4) the presence of warm ocean waters south of Greenland. For the 1889 episode, the Twentieth Century Reanalysis and historical records showed similar factors at work. However, markers of biomass burning were evident in ice cores from 1889 which may reflect another possible factor in these rare events. We suggest that extreme Greenland summer melt episodes, such as those recorded recently and in the late Holocene, could have involved a similar combination of slow climate processes, including prolonged North American droughts/heat waves and North Atlantic warm oceanic temperature anomalies, together with fast processes, such as excursions of the Arctic Oscillation, and transport of warm, humid air in Atmospheric Rivers to Greenland. It is the fast processes that underlie the rarity of such events and influence their predictability.

Identification of Air Masses Responsible for Warm Events on the East Antarctic Coast

“…These two periods were associated with passages of strong precipitation events, so-called atmospheric river (AR): poleward moisture was organized in a filamentary structure stretching from subtropical latitudes to Antarctica, leading to heavy snow accumulation events over DML (Gorodetskaya et al 2014). Note that, in Greenland, an AR event was observed in summer 2012 (e.g., Neff et al 2014), including water vapor isotope monitoring (Bonne et al 2015), and let to widespread melt at the ice sheet surface (Nghiem et al 2012). As observed over the Greenland ice sheet, T max rose at Syowa above the melting point during these events.…”

Investigating the local-scale influence of sea ice on Greenland surface melt

“…Several explanations have been put forth to explain this anomalous melt, including increased downwelling longwave radiation from low-level liquid clouds (Bennartz et al, 2013), advection of moist warm air over Greenland (Neff et al, 2014), and dominance of non-radiative fluxes (Fausto et al, 2016). While this event was likely a result of atmospheric circulation patterns that transported warm, humid air over the southern and western part of the ice sheet, the sea ice melt season began a week earlier than the 1981-2010 longterm mean over Davis Strait and 3 days earlier over Baffin Bay.…”

How does sea ice influence <i>δ</i><sup>18</sup>O of Arctic precipitation?

“…The observed 2012 Greenland melting was attributed to the following key factors: the North American heat wave, transitions in the Arctic Oscillation and transport of warm air and vapour via an atmospheric river (Neff et al, 2014;Bonne et al, 2014). Forcing the model with only oceanic conditions can thus not create a similar atmospheric-induced warming.…”