Greenland Surface Melt Due To Natural Variability, Not Global Warming – New Study

  • Date: 09/02/13
  • The Hockey Schtick

Last summer, the mainstream media breathlessly reported that a brief 4-day surface melt over the Greenland ice sheet represented evidence of man-made global warming. However, a paper published today in The Cryosphere finds that “the recent warmer summers over [the Greenland ice sheet] cannot be considered as a long-term climate warming but are more a consequence of [the natural North Atlantic Oscillation] variability affecting atmospheric heat transport.”

In other words, the brief Greenland surface melt was related to natural variability rather than alleged man-made global warming.

The Cryosphere, 7, 241-248, 2013
www.the-cryosphere.net/7/241/2013/
doi:10.5194/tc-7-241-2013

Brief communication ”Important role of the mid-tropospheric atmospheric circulation in the recent surface melt increase over the Greenland ice sheet”

X. Fettweis1, E. Hanna2, C. Lang1, A. Belleflamme1, M. Erpicum1, and H. Gallée3

1Laboratory of Climatology, Department of Geography, University of Liège, n°2 Allé du 6 Aout, 4000, Liège, Belgium
2Department of Geography, University of Sheffield, Winter Street, S10 2TN, Sheffield, UK
3Laboratoire de Glaciologie et Géophysique de l’Environnement (LGGE), n°54 Rue Moli\`re, 38402, Grenoble, France

Abstract. Since 2007, there has been a series of surface melt records over the Greenland ice sheet (GrIS), continuing the trend towards increased melt observed since the end of the 1990′s. The last two decades are characterized by an increase of negative phases of the North Atlantic Oscillation (NAO) favouring warmer and drier summers than normal over GrIS. In this context, we use a circulation type classification based on daily 500 hPa geopotential height to evaluate the role of atmospheric dynamics in this surface melt acceleration for the last two decades. Due to the lack of direct observations, the interannual melt variability is gauged here by the summer (June–July–August) mean temperature from reanalyses at 700 hPa over Greenland; analogous atmospheric circulations in the past show that ~70% of the 1993–2012 warming at 700 hPa over Greenland has been driven by changes in the atmospheric flow frequencies. Indeed, the occurrence of anticyclones centred over the GrIS at the surface and at 500 hPa has doubled since the end of 1990′s, which induces more frequent southerly warm air advection along the western Greenland coast and over the neighbouring Canadian Arctic Archipelago (CAA). These changes in the NAO modes explain also why no significant warming has been observed these last summers over Svalbard, where northerly atmospheric flows are twice as frequent as before. Therefore, the recent warmer summers over GrIS and CAA cannot be considered as a long-term climate warming but are more a consequence of NAO variability affecting atmospheric heat transport. Although no global model from the CMIP5 database projects subsequent significant changes in NAO through this century, we cannot exclude the possibility that the observed NAO changes are due to global warming.

Final Revised Paper (PDF, 3971 KB)   Supplement (1410 KB)   Discussion Paper (TCD)

The Hockey Schtick, 7 February 2013