June 17, 2013
Greenland Ice Sheet Had Record Melt In 2012 Due To Jet Stream
Lee Rannals for redOrbit.com — Your Universe Online
According to University of Sheffield research, published in the International Journal of Climatology, unusual Jet Stream changes were behind record surface melt of the Greenland Ice Sheet last summer.The Greenland Ice Sheet (GrIS) experienced a record surface melting in the summer of 2012, with more than 90 percent of the ice-sheet surface melting as of July 11, 2012. That was nearly double the previous record loss seen in 2010, when 52 percent of the GrIS surface had melted.
The team was able to confirm the record melting by using computer model simulations and satellite data. They also analyzed weather station data from on top of and around the ice sheet, showing several new high Greenland temperature records were set last summer.
The study showed that the record surface melting of the ice sheet was mainly caused by highly unusual atmospheric circulation and Jet Stream changes, which also caused last year's unusually wet weather in England. The analysis showed that ocean temperatures and Arctic sea-ice cover were relatively unimportant factors that helped lead to the record melting.
“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," said lead researcher Professor Edward Hanna from the University of Sheffield´s Department of Geography. "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."
He said they found that a "heat dome" of warm southerly winds over the ice sheet led to widespread melting. These Jet Stream changes did not show up in an Intergovernmental Panel on Climate Change (IPCC) computer model, which could indicate a flaw in this model.
"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," said Hanna. “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 centered over Greenland) and polar jet stream which favored southerly warm air advection along the western coast."
He said the next five to 10 years will reveal whether or not 2012 was a rare event 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," the researcher said. "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.”
Scientists have been trying to determine what led to the 50-year-record ice melt in Greenland. In April a team of scientists wrote in the journal Nature that they determined that the ice melt could be due to thin cloud cover.
“Clouds are still one of the greatest uncertainties in climate models. Even though the current climate models are generally correct, we need better measurements to improve them,” Von P. Walden, principal investigator for the ICECAPS project, said in an NSF statement in April. “We´re doing this to avoid future surprises, and we need to expand our knowledge of the details of how the climate operates.”