June 20th, 2013 by James Ayre
The exceptional ice-surface melt of the Greenland Ice Sheet in 2012 was caused by changes that occurred in the jet stream, according to new research from the University of Sheffield. This matters because it means that the Greenland Ice Sheet may melt faster than has been predicted by climate models…
During the summer of 2012 more than 90% of the Greenland Ice Sheet’s surface melted — greatly exceeding the previous surface-melt record for the Greenland Ice Sheet, which was set just two years earlier in 2010. While the melt can certainly be attributed to climate change, what were the exact causes of such an unprecedented melt? Will the ice sheet be melting faster than has been predicted?
To answer these question, researchers from the University of Sheffield used a combination of satellite data, computer model simulations (SnowModel), and weather station data from on top of and around the Greenland Ice Sheet (GrIS), to analyze the 2012 melt event.
The findings have clearly demonstrated “that the record surface melting of the GrIS was mainly caused by highly unusual atmospheric circulation and jet stream changes, which were also responsible for last summer’s unusually wet weather in England.”
Professor Edward Hanna from the University of Sheffield’s Department of Geography said: “The GrIS is a highly sensitive indicator of regional and global climate change, and has been undergoing rapid warming and mass loss during the last 5-20 years. Much attention has been given to the NASA announcement of record surface melting of the GrIS in mid-July 2012. This event was unprecedented in the satellite record of observations dating back to the 1970s and probably unlikely to have occurred previously for well over a century.”
“Our research found that a ‘heat dome’ of warm southerly winds over the ice sheet led to widespread surface melting. These jet stream changes over Greenland do not seem to be well captured in the latest Intergovernmental Panel on Climate Change (IPCC) computer model predictions of climate change, and this may indicate a deficiency in these models. According to our current understanding, the unusual atmospheric circulation and consequent warm conditions of summer 2012 do not appear to be climatically representative of future ‘average’ summers predicted later this century.
“Taken together, our present results strongly suggest that the main forcing of the extreme GrIS surface melt in July 2012 was atmospheric, linked with changes in the summer North Atlantic Oscillation (NAO), Greenland Blocking Index (GBI, a high pressure system centred over Greenland) and polar jet stream which favoured southerly warm air advection along the western coast.
“The next five-10 years will reveal whether or not 2012 was a rare event resulting from the natural variability of the NAO or part of an emerging pattern of new extreme high melt years. Because such atmospheric, and resulting GrIS surface climate, changes are not well projected by the current generation of global climate models, it is currently very hard to predict future changes in Greenland climate. Yet it is crucial to understand such changes much better if we are to have any hope of reliably predicting future changes in GrIS mass balance, which is likely to be a dominant contributor to global sea-level change over the next 100-1000 years.”
The new findings were just published in the International Journal of Climatology.
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