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New Study Shows How Fast Ice Sheets Can Change

How high and how fast sea level will rise is a crucial question for the coming century, and it all depends on how fast the giant ice sheets atop Greenland and Antarctica melt back and slide into the ocean as the planet warms. To try and figure out how rapidly ice sheets respond to climate change, scientists look to the ancient past — and a new paper released Thursday in Science says that ice can respond a lot faster than anyone had thought. 

During a very brief episode of cooling that happened about 8,200 years ago, glaciers spread across Baffin Island, in the Canadian Arctic, at an almost astonishing pace, said the authors. “Based on the prehistoric record,” said lead author Nicolás Young, at the Lamont-Doherty Earth Observatory near New York City, “ice sheets can respond really quickly to short-term and modest temperature change.”

Credit: NASA

That’s an important and worrisome conclusion. Scientists have already measured a sea level rise of 8 inches over the past century, and their best projections suggest another 3 feet or so by 2100, as ice sheets melt and slide into the ocean. That seems to be happening faster all the time. This summer alone, ice experts noted unusually widespread melting in Greenland, along with the disintegration of part of a major glacier. No one knows for sure whether the melting might accelerate, leading to even faster-rising seas. 

While this new study addresses the growth of ice sheets — the last thing anyone is concerned about in a warming world — the fact that ice can spread so quickly in such a short time suggests it could retreat quickly as well.

In this case, “short time” is 150 years — the length of the cooling interlude known to paleoclimatologists as the 8.2-ka Event. At that point, global temperatures were on the rise, and the glaciers that had dominated the Earth during the last Ice Age were in full retreat. Meltwater from the giant Laurentide Ice Sheet had formed a gigantic freshwater lake known as Lake Agassiz just south of Hudson Bay, which was bigger than all of the Great Lakes combined.

As the planet kept warming, a natural dam made of ice burst, and trillions of gallons of water emptied from Lake Agassiz into Hudson Bay, and from there into the North Atlantic, where it disrupted a major ocean current that brings warm water northward to Europe and North America.

With this meridional overturning circulation shut down, the region cooled by about 4-7° F, and stayed that way for about 150 years.

That’s just a blink of the eye in geologic time, but it’s about the same amount of temperature change that climate scientists project for the coming century. That being the case, Young said, “one of the main questions we need to answer is whether ice sheets can respond on timescales that matter to humans.”

To try and find out, Young, who was at the University at Buffalo at the time, made the trek with his co-authors to Ayr Valley, on Baffin Island, in Arctic Canada, to look for rocks pushed ahead of expanding glaciers, then left behind when the glaciers retreated.

What they found was that glaciers grew dramatically, virtually overnight. Not only that: they grew bigger in just 150 years than they’d grown during a much longer episode of cooling known as the Younger Dryas, when temperature dropped even more and stayed low for 1,200 years.

The difference, the scientists believe, is that while average temperatures were lower in the Younger Dryas, summers may actually have been cooler during the shorter 8.2-ka Event. That would have kept glaciers from melting much during the summers, giving them a head start on expansion during the following winters.

Expanding glaciers is not something anyone is worried about at the moment, of course — it’s the retreat, along with the resulting sea level rise, that has everyone worried. But the more scientists can understand about how glaciers and ice sheets respond to climate change in both directions, the better they can project what’s likely to happen in the near future.

“Classically, the retreat of glaciers and ice sheets happens more quickly than the advance,” Young said. “Now we’re showing that the advance can happen as quickly as well.”

That being the case, Young said it’s a good bet that what happens to the ice on Greenland, especially, where the ice sheet is looking increasingly precarious, “is going to be tightly coupled to temperature change over the next century.”

Nobody thinks all of Greenland’s ice will melt away by 2100 — a very good thing, since that could raise sea level by a catastrophic 20 feet or more. But given what scientists are learning about how ice sheets respond to temperature, there’s still plenty to worry about. 

Related coverage
The Bad News Continues to Flow About Antarctica’s Ice
How a Patch of Ocean Helps Keep Europe from Freezing
Climate and Carbon: The Link Just Got Stronger
Greenland Ice Sheet Melt Nearing Critical ‘Tipping Point’


By Lewis Cleverdon
on September 13th, 2012

“This summer alone, ice experts noted unusually widespread melting in Greenland, along with the disintegration of part of a major glacier. No one knows for sure whether the melting might accelerate, leading to even faster-rising seas. “

With respect, might it be more accurate to say that;

“This summer alone, ice experts noted unusually widespread melting in Greenland, along with the disintegration of part of a major glacier. With the outflow of ice and meltwater from Greenland rising at an average of over 10% per year for the last decade, no one knows for sure just what, if anything, would halt that exponentially rising rate of melting. If it somehow continued unchanged, it would clear the entire ice cap down to a huge landlocked melt-lake by about 2080.”



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By Steve Bloom
on September 14th, 2012

Well, “no one knows for sure” whether the sun will rise tomorrow.  It’s a phrase that when used selectively, as here, communicates (incorrectly) added uncertainty.

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By Lewis Cleverdon
on September 15th, 2012

Steve - its not clear whether your response is to both Michael and I, but acknowledging increased uncertainty (over the orthodox assumptions of Greenland melt rate) seems to me reasonable. There are a number of factors in play, some of which are not accounted in the somewhat dated science the orthodoxy relies on.

For instance, the drivers of exponentially accelerating ice mass loss include:
- rising air temperatures from global warming, from a warming Atlantic, and from a warming Arctic Ocean under increasing ice cover loss;
- rising extreme insolation from the emerging annual phenomenon of the Greenland Summer High;
- rising precipitation from the northward migration of rainfall, of which an increasing fraction is falling as rain, with both a direct heat transport effect, and an increased lubrication effect via moulins, and a destruction of reflective snow cover over the darker ice cap;
- rising fallout of soot and other particulates causing cryonite melt holes across the surface;
- rising incidence of very large numbers of minor earth tremors reflecting just the mass-loss so far further mobilizing the glaciers.

Most of these factors would be further accelerated by the ongoing acceleration of the mega-feedbacks present in the arctic as sea-ice loss progresses, and as they start to interact with eachother, if we were to fail to apply effective Albedo Restoration measures across the Arctic Ocean.

From this perspective, while I don’t see that current reductionist science is anywhere near being able to model multiple feedback interactions with random event contributors, it seems reasonable to expect a rise in the exponent of Greenland Ice Loss up to the point where the cap is reduced to a shallow dome over the central land depression within encircling mountains, after which the loss of gradient to the passes between mountains would slow the the mass-loss rate down to melt-water output only.

Given that a mere 3 metres of SLR would be ruinous for the world’s coastal cities holding much of society’s population and economy, and that Greenland ice is of course only a part of the problem, I’d suggest that we need to get very much louder about the prospects of the latter’s super-exponential mass-loss, as well as facing the need of shifting the debate on well supervised geo-engineering under a UN climate treaty from ‘whether’ to ‘when’.



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By Lewis Cleverdon
on September 16th, 2012

Apologies for a typo above. Para 2 line six should read:

- rising fallout of soot and other particulates causing cryoconite melt holes across the surface;


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