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Greenland’s Ice Loss May Slow, But Coasts Still At Risk

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The flow of Greenland’s glaciers toward the sea may have increased significantly in the past decade, but a new report in Nature finds that rate of increase is unlikely to continue. “The loss of ice has doubled in the past 10 years, but that doesn't mean it's going to double again in the next ten years,” said lead author Faezeh Nick, a glaciologist at the University Centre in Svalbard, in Longyearbyen, Norway, in an interview.

That conclusion, based on a new, sophisticated computer model, makes the worst-case scenario of sea level rise — an increase of 6 feet or so, on average, by 2100 — look less likely to play out.

Since the heat-trapping gas that has already put into the atmosphere will be there for hundreds of years to come, Greenland will continue to melt indefinitely. The fact that it may not happen quite as fast as the worst-case scenarios might forecast isn’t all that reassuring.
Credit: flickr/Howard Ignatius

That’s the good news. The bad news is that, in the model at least, the slowdown doesn’t necessarily bring glaciers back to their original, stately rate of flow. And since the heat-trapping gas that has already put into the atmosphere will be there for hundreds of years to come, Greenland will continue to melt indefinitely. The fact that it may not happen quite as fast as the worst-case scenarios might forecast isn’t all that reassuring.

Because even if sea level goes up by only half that much, the combination of rising seas and periodic storm surges could devastate coastal areas around the world. Scientists have concluded, based on earlier studies, that the lower figure of about 3 feet is most likely, and while that research didn’t explicitly calculate anticipated sea level rise, it appears consistent with those estimates.

Earlier studies, based on satellite observations, had also noted that Greenland’s ice flow has started to slow, which means the dumping of icebergs into the ocean should slow as well. Projecting what’s likely in the future, however, is the province not of observations but of models. In this case, Nick and a half-dozen colleagues used a new model that factors in the effects of climate change on both the air above Greenland and on the ocean below.

Those effects, Nick said, depend on the characteristics of individual glaciers. The Petermann glacier in northwest Greenland, for example — one of four the scientists modeled — “has a very long floating shelf, so it’s very sensitive to ocean warming.” As a result, the Petermann has loosed two massive “ice islands” into the sea, one in 2010 that was four times the size of Manhattan, and another, about half as big, in 2012.

But while those were major events, they didn’t affect the Petermann’s overall flow rate significantly. Other glaciers, such as the Jacobshavn, respond to warmer seas not just by letting loose big chunks of ice, but also by flowing more quickly. The reason: Jacobshavn’s ice was mostly grounded on the sea floor, not floating, creating tremendous friction that kept the upstream parts of the glacier in check. When that grounded ice is removed, it’s as though the brakes suddenly came off.

Even if sea level goes up by only half as much originally anticipated, the combination of rising seas and periodic storm surges could devastate coastal areas around the world.
Credit: flickr/Bruno Sanchez-Andrade Nuño

Warmer air temperatures, meanwhile, melt ice on top of the glaciers, and on the massive ice sheet they flow out of. In the summer of 2012, in fact, for the first time in more than a century, virtually the entire surface was at least partially melting for a few days in July (the reason, some scientists believe, was not just warmer-than-normal air temperatures overall, but also the heat-trapping effect of thin clouds).

Eventually, all of this water flows to the sea, but along the way it funnels down into crevasses in the ice, which can help lubricate the ice-rock interface at the bottom, letting glaciers flow faster. Downflowing water can also widen cracks in the ice, Nick said, which can enhance disintegration of the glacier’s leading edge already weakened by the warming ocean.

Feeding all of these effects into their model, the scientists found that speedup in the flow of glaciers into the sea is something to be expected in a generally warming climate, but that it won’t simply get more and more pronounced. “You see a big jump,” Nick said, “and then it slows down again.”

Editor's Note: The headline of this article has been changed to reflect the fact that the study concerns projections of future glacier melt rates, and not, as the previous study indicated, observations of a recent slowdown.

Related Content 
Ice is Flowing Slower on Greenland than Many Feared
Greenland Sheds a ‘Mega-Berg’
Greenland Glacier Sheds Two Manhattans' Worth of Ice
NASA Eyeballs Glacial Melt in Greenland
Greenland Melt Sets Record Weeks Before Summer Ends
The Story Behind Record Ice Loss in Greenland
Clouds Helped Enhance Greenland's Record Melting 

Comments

By Dave (Basking Ridge, NJ 07920)
on May 8th, 2013

This paper focuses on a model which projects future dynamic ice loss (calving) from Greenland glaciers and in an interview it is suggested that Nick provided some broader and optimistic conclusions about overall SLR based on that. In this respect I think a factor of 2 less SLR than previously thought can be viewed as significant optimism. So I would like to know a little more about that estimate and the basis for it. If this were true then it would be a world news scoop!! Anyway, I understand that ice dynamics is an area of significant uncertainty so I hope he is right. But I also wonder about contributions from Antarctica in a warming world (2.8C by 2100 was one scenario mentioned) and how well the Nick (et al) model might be considered to apply there.

 

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By Elmar Veerman (Leiden, Netherlands)
on May 9th, 2013

The headline is still misleading. Greenland’s ice loss will not slow down but speed up. The rate of increase in ice loss is expected to fall.

Reply to this comment

By Dave (Basking Ridge, NJ 07920)
on May 9th, 2013

Thanks Elmar. That was my guess but I only had the abstract. Good luck with EUSJA.

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By Mauri S Pelto
on May 9th, 2013

A close examination of the figures and text of this paper there is no indication that Greenland Ice Sheet mass loss will slow for the four glaciers.  The main point from this excellent team of glaciologists is that the outlet glacier will not continue to accelerate.  The current rate of sea level rise will not only be maintained but will accelerate even from these four glaciers after 2050, according to Figure 3 in the paper.  Figure 1 in their paper indicates one glacier that is not modeled that is as crucial to the ice sheet, Zachariae Icestream the blue finger heading into the center of the ice sheet from the northeast region.

Reply to this comment

By Dave (Basking Ridge, NJ 07920)
on May 10th, 2013

Professor Pelto:

Thank you. As a glaciologist, I was wondering what your personal perspective is of SLR? There is so much inherent uncertainty factored into it, all the way from emissions scenarios to projected temperatures, ice dynamics and so on and so on, that once all of that gets bounced around and digested the media commonly just says 3 feet by 2100, which seems oddly precise. Others expand a little and commonly quote 3 feet / 1m and 6 feet as less likely but possible. I at least tend to think of a range. For instance, 0.8m to 2m SLR by 2100 seems like a rough catchall from the papers I have read, which is most certainly not all of them. So, without holding you to anything [ smile ] dare I ask what makes most sense to you for a SLR projection by 2100?

Thanks indeed if you reply.

Reply to this comment

By Mauri S Pelto (West Boylston)
on May 11th, 2013

What makes the most sense is not a specific number, but rather a true forecast which looks at the probability of certain outcomes, which does generate a range, but the range has probabilities attached.  Part of the probability in this case is the difference in how much the climate will warm.  I dare say that the Greenland Ice Sheet losses which has increased from an annual SLR input of 0.2 mm to 1.0 mm over the last 20 years, will not continue this rate of increase, but will also not decrease from the current level.

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By Dave (Basking Ridge, NJ 07920)
on May 11th, 2013

I appreciate your answer. Thanks so much. A forecast range with an associated distribution of likelihoods is fine in publications and because that’s how it is. But it is also not snappy language for everyday. It could obviously use a bit more focus in the media than it is getting, to at least teach that a particular single number for SLR should not be clung to quite so hard.  But how to do it?  It might be nice for someone to first try coming up with some consistent everyday language – words or graphics - that can nevertheless still effectively communicate SLR projections, along with an appropriate sense of the important caveats.

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