An unusual shift in the jet stream triggered the historic level of surface ice melt that occurred across Greenland last summer, a new study says. Using satellite data and a computer model simulation, scientists from the University of Sheffield found that a high-pressure system developed in the mid-troposphere over Greenland for much of the summer, pushing warm southerly winds over the western edge of the ice sheet and creating a “heat dome” over Greenland. According to the study, published in the International Journal of Climatology, this unprecedented event caused record melting across virtually the entire ice sheet, including on Summit Station, Greenland’s highest peak. Ocean temperatures and Arctic sea ice retreat, meanwhile, played a minimal part in the record surface ice melt, the scientists reported. The study predicted that the record ice melt of 2012 is not likely to be “climatically representative of future ‘average’ summers” during the coming century.