Extreme melting in Greenland’s ice sheet last summer was linked to warm air delivered by the wandering jet stream (seen here), which has been linked to extreme warming in the Arctic. Credit: NASA
Excerpt:
A group of scientists found that Greenland had shown much more unusual melting in its colder northern stretches than in the warmer south, and that this had occurred because of very strange behavior in the atmosphere above it. During the month of July, an atmospheric phenomenon called a “cutoff high” — a region of high pressure that stayed relatively immobile over the ice sheet, bringing with it sustained sunny conditions — lingered for many days and produced unusual warmth at the surface and record melting for northwest Greenland.
A cutoff high “describes this atmospheric high pressure system that detaches from the jet stream, in this case, and then basically sits there, it’s almost like living by itself,” said Marco Tedesco, the lead author of the study just published in Nature Communications, and a researcher with the Lamont-Doherty Earth Observatory at Columbia University.
The high was accompanied, in this case, by a northward departure of the mid-latitude jet stream — a stream of air in the northern hemisphere that can travel in a more or less wavy route as it progresses from west to east — that set a record for its northward extent, the study found.
“I think we can start to connect these dots and say that increasing loss of Arctic sea ice is leading to more blocking patterns, which are contributing to the increasing surface melt on Greenland,” said Jennifer Francis, the Rutgers University Arctic expert whose ideas about Arctic melting distorting the jet stream have ignited one of the biggest ongoing debates in climate science, and who is familiar with the new study by Tedesco and his colleagues. “Of course, this is bad news for sea-level rise and maybe also for the ocean circulation as the extra meltwater appears to be partially responsible for the ‘Cool Blob’ south of Iceland.”
