Posted by: goodcoldwater | October 5, 2009

Greenland ice sheet: sensitive + melting fast

About 10% of the world’s fresh water is stored in the Greeland ice sheet: a cap of freshwater ice that covers more than 50,000 km² of inland Greenland’s landmass.

If the Greenland ice sheet melts completely, predictions are that the release of that 10% of water will raise our planet’s sea level about 7 metres.

Scientists seem to agree on these points; debates – and the research – centre on anticipating how quickly the Greenland ice sheet is melting, how fast it will melt over the next decades, and whether that melt can be slowed.

Greenland Icesheet

(Image of the ice sheet’s summit from Greenland news agency Sermitsiaq’s website, on Sept 29/09. The temperature was a record minus 46.0 ° C.)

On September 23, The Guardian reported that scientists from several international research groups used data from Nasa’s ICESat (Ice, Cloud and and land Elevation Satellite) to piece together a picture of the changing fortunes of glaciers on the ice sheets. The satellite bounces laser light off the ground, producing surprisingly precise measurements of land, ice and water surfaces.

In Greenland, glaciers in the south-east were found to be flowing at speeds of more than 100m per year, during which they thinned by 84cm. More slow-going glaciers lost around 12cm a year.

Research about the Greenland ice sheet’s melt has been in the news regularly this year, as the science community knows those vast kilometres of ice contain important information about climate change. The Globe and Mail also reported on Sept. 23 (unfortunately without much detail) that:

New satellite information shows that ice sheets in Greenland and western Antarctica continue to shrink faster than scientists thought and in some places are already in runaway melt mode…. Research found that 81 of the 111 Greenland glaciers surveyed are thinning at an accelerating, self-feeding pace.

That’s a dramatic statement – 81 of 111 Greenland glaciers are thinning more quickly than previously expected. Not a pretty number to present to anyone who’s living on a coastline.

The Greenland ice sheet is unique for other reasons too:

  • it’s farther from the north pole than Antarctica is from the south pole, which makes it more sensitive to climate change;
  • when it calves into the Denmark Strait, the Greenland ice sheet touches on the warmer waters of the Gulf Stream (Arctic ocean ice doesn’t have to deal with these kinds of softening temperatures);
  • and Greenland is easier to get to than Antarctica, so smaller, more temporary research projects can be sent there.

In Copenhagen this past March, Konrad Steffen, an ice expert at the University of Colorado, told a global warming conference what his team had found when they used a special camera (with NASA’s help) to record what was going on inside the Greenland ice sheet. 

a very active moulin on the Semilik Glacier; Konrad Steffen + research team put cameras down moulins in 2007 to see what was happening inside the glacier's "pipe" system (photo Konrad Steffen, U Colorado)

A very active moulin on the Greenland ice sheet; Konrad Steffen + research team put cameras down moulins in 2007 to see what was happening inside several glaciers' "pipe" systems (photo Konrad Steffen, U Colorado)

The footage, taken 100m inside the ice,  revealed a complex subglacial network of interconnecting tunnels carrying water from the surface to deep inside the ice sheet. Here’s a link to a brief video inside that cold waterworks: http://www.guardian.co.uk/environment/video/2009/mar/12/greenland-glacier-channels

“The discovery could explain sudden and severe increases in ice movement seen during peak summer,” Steffen said. “Water channelled from the surface to the base of the ice sheet could speed up the way it slides across the bedrock. On a large scale, this could cause the ice sheet to break up much faster than expected.” The article continues:

Combined with images from a ground-penetrating radar dragged across the ice surface, Steffen’s results showed that the moulin quickly widened beneath the surface. Several side channels carried water away to other parts of the ice sheet and fed the moulin from other holes on the surface. “The whole ice sheet is connected with these open channels,” he said.

A slightly earlier Guardian article, from Sept. 1, focused even more closely on the Greenland ice sheet and the Sermilik fjord in particular. Reporter Patrick Barkham interviews Gordon Hamilton, a Scottish-born glaciologist from the University of Maine’s Climate Change Institute, and Hamilton’s discoveries are arresting:

“When we arrived there was no glacier to be seen. It was way up the fjord,” Hamilton says. “We thought we’d made some stupid goof with the co-ordinates, but we were where we were supposed to be.” It was the glacier that was in the wrong place. A vast expanse had melted away.

When Hamilton and Stearns processed their first measurements of the glacier’s speed, they thought they had made another mistake. They found it was marching forwards at a greater pace than a glacier had ever been observed to flow before. “We were blown away because we realised that the glaciers had accelerated not just by a little bit but by a lot,” he says.

The three glaciers they studied had abruptly increased the speed by which they were transmitting ice from the ice sheet into the ocean.

As Hamilton has found, Greenland’s glaciers have increased the speed at which they shift ice from the sheet into the ocean. Helheim, an enormous tower of ice that calves into Sermilik Fjord, used to move at 7km (4.4 miles) a year. In 2005, in less than a year, it speeded up to nearly 12km a year. Kangerdlugssuaq, another glacier that Hamilton measured, tripled its speed between 1988 and 2005. Its movement – an inch every minute – could be seen with the naked eye.

The Sermilik Fjord, Getty Images

The Sermilik Fjord, Getty Images

In other words, the major change in terms of global ice activity is that the Greenland ice sheet is now shedding more ice than it is accumulating.

The melting has been recorded since 1979; scientists put the annual net loss of ice and water from the ice sheet at 300-400 gigatonnes.

This could mean that the sea level will rise up to 2 levels in the next decade. Correct me if I’m wrong, but it looks like we’ll be seeing something no living generation has a memory of – what will we do with this unique situation, besides palpitate with anxiety?

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Responses

  1. Good stuff the changes are beyond what I would have imagined based on my work on the ice sheet was examining its susceptibility to this in the 1980’s. The Guardian video, showing a camera lowering down the moulin. Moulins have always been present in this part of the ice sheet. They will be carrying more water and may be more numerous. these features do not lead to large scale or long term glacier acceleration, nor do they weaken the ice. It is not clear who added the captions, but I doubt Steffen would conclude that would lead to ice sheet breakup.
    http://www.realclimate.org/index.php/archives/2008/04/moulins-calving-fronts-and-greenland-outlet-glacier-acceleration/
    and http://glacierchange.wordpress.com/2009/06/28/recession-of-jakobshavn-isbrae/

  2. hi Mr Spelto,

    thanks a lot for taking time to read this post and comment on it. I’m aware that moulins are a natural part of glaciers, but my glacier knowledge is quite fledgling so any additions & corrections are appreciated.

    I see from the link on your name that you’re connected with the North Cascade Glacier Climate Project, so I’d love to draw on your knowledge. In particular, could expand a bit more on the relationship (or not) between moulins and accelerated glacial melting?

    my impression from the articles that I quoted was that meltwater (becoming groundwater once it passes through moulins) was a major factor in the acceleration of glacial melt.

    the April 08 RealClimate article you attached here suggests that that *used* to be the theory but now the current thinking is that glacial thinning at the front of a glacier is more the source of rapid melting.

    And yet, coming back to the Steffen quote I used, which is from The Guardian in Mar 09, there seems to be an emphasis again on water flowing through the moulins: “Water channelled from the surface to the base of the ice sheet could speed up the way it slides across the bedrock. On a large scale, this could cause the ice sheet to break up much faster than expected.”

    In your view, how do those two models of glacial melting intersect? Thanks in advance for your info & analysis.


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