Ground truth for satellite data For other researchers, Summit Camp is a brief stop on longer journeys to the uninhabited interior of Greenland's ice sheet.

Liz Morris, a glaciologist from the Scott Polar Institute at Cambridge University, spent a few days at the station in mid-July, organizing her supplies for a monthlong, 500-mile expedition across the ice.

It's the seventh such journey Morris has undertaken since 2004, all of them aimed at measuring the density of the top layer of snow covering the ice sheet. Morris uses the information she gathers on these trips to check the accuracy of data collected by a European satellite, Cryosat-2, that tracks changes in the thickness of polar ice -- information that tells scientists how quickly that ice is thawing.

"The problem about satellites is that they will give you the change in height [of snow] but not change in mass," Morris said. That doesn't provide a full picture of snow accumulation, since it doesn't take into account the density of the snow layers that pile on the ice.

That's where Morris and her assistant, John Sweeny, come in. The pair left Summit Station on July 17 equipped with a pair of Ski-Doo snowmobiles pulling cargo sleds. They planned to spend a month traveling an established track along Greenland's ice, along the way drilling boreholes to measure the density of the topmost layers of snow.

Several recent studies, most based on satellite data, have concluded that warming has accelerated ice loss from Greenland's massive ice sheet. But Morris noted that most of that loss occurs at the margins of the ice sheet, particularly in areas where the edges of glacial ice are in contact with the ocean.

It's not clear whether the ice in Greenland's interior, which rests on bedrock, is as vulnerable to warming, Morris said -- a question that the data she collects could help answer.

"At the end of the day, it's clear that if the world gets warmer, ice is going to melt," she said. "The question is, is this just a response to short-term ocean warming, and will it continue?"

Reprinted from Climatewire with permission from Environment & Energy Publishing, LLC. www.eenews.net, 202-628-6500

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