|Many glaciologists believe that snow/ice melt in Greenland could equate to a 1 meter increase in ocean levels, something that would be devastating to a major portion of the human population|
World oceans would rise 23 feet and flood many coastal areas if climate change melted the entire Greenland ice cap. And satellite images from 1980 onward reveal the surface of this vast ice sheet is warming, getting soggy and staying wet for longer periods every year.
However, preliminary research by The University of Montana and its partners suggests some of this meltwater does not reach the ocean to contribute to sea-level rise. Instead it infiltrates downward into colder snow and refreezes into ice layers that can be more than a foot thick. These layers are fragmented, so water can’t flow atop them for long before draining downward again and freezing in place.
“We are still working up our results, but so far this is good news concerning worries about Greenland’s role in the sea level rise we see happening today,” said UM glaciologist Joel Harper. “Since many of the ice layers that form during a year of heavy melt are discontinuous, the next year’s melt can’t travel along the ice layers as a means of escaping the ice sheet.”
He said it’s so dark and cold during Greenland winters that even with some winter warming the snowpack is still extremely cold going into summer, “and summer melting always will have a hard time warming a snowpack laden with cold dense ice layers.”
Harper was part of a six-person scientific expedition that ventured onto the Greenland ice sheet for a month during June and July. They lived in tents high atop the ice cap at about 6,600 feet in a white, featureless landscape swept by endless wind. To do its work, the group made 60- to 70-mile journeys down into the melt zone closer to Greenland’s west coast, using snowmobiles to pull scientific gear and expedition members on skis.
Harper said their research was funded by a $524,000 National Science Foundation grant. His project collaborators are Tad Pfeffer of the University of Colorado and Neil Humphrey of the University of Wyoming. Each scientist brought one graduate student to complete the team.
The researchers drilled 21 35-foot-long ice cores during the course of their work. They also dug many snow pits and did numerous experiments with colored dye to track meltwater flow. In addition, they installed two meteorological stations and used radar to map ice layers beneath the snow.
In five boreholes located in sequentially lower elevations across a 25-mile span, the team also installed vertical strings of temperature sensors to note melting and freezing events in the snow up to 35 feet deep. (When water freezes it releases heat – a thermal signature that can be detected.) Harper said the sensors – called thermisters – have their own power source and will record data until researchers retrieve them next year.
He compared the Greenland ice cap to pancake batter. In its middle at higher elevations there is more snowfall than melting. As more snow is poured on, it compresses the vast sheet, which flows outward toward the warmer coasts where there is more melting.
The team had two snowmobiles to haul six people and their gear down to the melt zones to do their research. The landscape is utterly devoid of landmarks, so they used global positioning systems to navigate during the three-hour traverses. Two scientists drove, while the rest were towed behind the snowmobiles on skis.
“While skiing, we put on every bit of clothing we had and an iPod because you were standing behind these snowmobiles for three hours or more,” Harper said. “We would use a bike tire as a harness clipped to the rope. So we would just stand there and try not to fall asleep as we were pulled along.”
Harper, who was a competitive skier as a youth in Colorado, also tried using a sail to kite ski across the ice cap. His power source was Greenland’s endless katabatic winds, which are caused by dense cold air atop the ice sheet flowing downward toward the warmer coasts.
“A lot of times it was too windy – you could get up to 30 mph no problem,” he said. “I could get screaming along – and I’m used to speed – but this was on the edge. I found it was too hard to navigate long distances with GPS when you are trying to fly the kite and not crash. It just wasn’t compatible with the whole group, so in the end it was more for fun.”
He said some of the melt zone contained barely wet snow, while others areas were a “slush swamp” of super-saturated snow that a person without skis could sink into like quicksand. The expedition had to make the long traverses from base camp because members didn’t dare camp in the melt zone. Too much thawing could bog down their snowmobiles and leave the researchers stranded in an area where ski planes can’t land. They might be stranded in the soggy snow until the next freeze.
“And if the snow machines would break, you couldn’t possibly ski back in a day,” he said. “It’s too far.”
Harper said his group will return next year to study another 75-mile stretch of the ice cap. They will start at the lowest elevation examined last summer and continue downward toward the coastal melt zone. The expedition will begin earlier in the year so the snow won’t be as treacherous at lower elevations.
“This is one reason why our results are preliminary,” he said. “We only have half the story. I suspect things might really be moving down below, but so far in the upper part of the ice sheet, we have thrown that out. In that area we found the melt is increasing every year, but it isn’t going anywhere.”
Harper said they decided to study the west side of the ice cap because it is accessible from the town of Kangerlussuaq, which is the logistics headquarters for science in Greenland. The ice they studied also is the headwaters of Jakobshavn, one of Greenland’s big calving glaciers that has increased speed in recent years. Their base camp was a three-hour plane ride from Kangerlussuaq.
“There was nothing special about our camp,” he said. “It was just some GPS coordinates we selected in the middle of nowhere. We got nailed by a big storm right after we arrived, but after that temperatures stayed between about 10 and 35 degrees Fahrenheit.”
Harper said their work might partially explain why Greenland isn’t a larger player in current sea-level rises despite its enormous ice cap. A 2007 article in the journal Science contends Greenland contributes about 0.5 millimeter to ocean level rise annually, while smaller glaciers scattered around the globe contribute 1.1 millimeter to sea-level rise.
“Other recent work shows that ice loss from small glaciers and ice caps like those in Montana dominate current sea-level rise and will likely continue to dominate sea-level increases for at least the next 50 years,” he said. “Since there are several hundred thousand small glaciers around the world, the sea-level rise we expect from them is still very significant.
“I don’t know of any glaciologist who thinks anything like a 6-meter (19.8 foot) sea-level rise is in the cards by the end of the century,” Harper said, “but even 1 meter – which is at the upper end of what we currently think might be possible – would be a very big deal.”