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Nature: “Dynamic thinning of Greenland and Antarctic ice-sheet ocean margins is more sensitive, pervasive, enduring and important than previously realized”

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"Nature: “Dynamic thinning of Greenland and Antarctic ice-sheet ocean margins is more sensitive, pervasive, enduring and important than previously realized”"

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The most detailed satellite information available shows that ice sheets in Greenland and western Antarctica are shrinking faster than scientists thought and in some places are already in runaway melt mode, a new study found….

Using 50 million laser readings from a NASA satellite, scientists for the first time calculated changes in the height of the vulnerable but massive ice sheets and found them especially worse at their edges. That’s where warmer water eats away from below. In some parts of Antarctica, ice sheets have been losing 30 feet a year in thickness since 2003, according to the study….

“To some extent it’s a runaway effect. The question is how far will it run?” said lead author Hamish Pritchard of the British Antarctic Survey. “It’s more widespread than we previously thought.”

That’s from “Study: ‘Runaway’ melt on Antarctica, Greenland,” the pull-no-punches MSNBC story last month.  The full study, “Extensive dynamic thinning on the margins of the Greenland and Antarctic ice sheets,” was published in Nature (subs. req’d, excerpted below).

NASA Ice Satellite Maps Profound Polar Thinning

The British Antarctic Survey put out a news release with graphics.  Here are some satellite tracks, from NASA’s ICESat (Ice, Cloud, and land Elevation Satellite), revealing areas of dynamic thinning (red) in Antarctica and Greenland [click to enlarge].

The release notes that this “dynamic thinning”:

  • reaches all latitudes in Greenland
  • has intensified on key Antarctic coastlines
  • is penetrating far into the ice sheets’ interior and
  • is spreading as ice shelves thin by ocean-driven melt.

The authors conclude “Ice shelf collapse has triggered particularly strong thinning that has endured for decades.”  More of the MSNBC story:

Some of those areas are about a mile thick, so they’ve still got plenty of ice to burn through. But the drop in thickness is speeding up. In parts of Antarctica, the yearly rate of thinning from 2003 to 2007 is 50 percent higher than it was from 1995 to 2003.

These new measurements confirm what some of the more pessimistic scientists thought: The melting along the crucial edges of the two major ice sheets is accelerating and is in a self-feeding loop. The more the ice melts, the more water surrounds and eats away at the remaining ice.

What’s going on in Antarctica may be even more worrisome than what’s happening in Greenland, as I’ve noted (see Large Antarctic glacier thinning 4 times faster than it was 10 years ago: “Nothing in the natural world is lost at an accelerating exponential rate like this glacier” and “Q: How much can West Antarctica plausibly contribute to sea level rise by 2100?” [A:  3 to 5 feet]).

Antarctica is disintegrating much faster than almost anybody imagined.  In 2001, the IPCC “consensus” said neither Greenland nor Antarctica would lose significant mass by 2100. They both already are.  As Penn State climatologist Richard Alley said in March 2006, the ice sheets appear to be shrinking “100 years ahead of schedule.”

The warming of the WAIS is most worrisome (at least for this century) because it’s going to disintegrate long before the East Antarctic Ice Sheet does “” since WAIS appears to be melting from underneath (i.e. the water is warming, too), and since, as I wrote in the “high water” part of my book, the WAIS is inherently less stable:

Perhaps the most important, and worrisome, fact about the WAIS is that it is fundamentally far less stable than the Greenland ice sheet because most of it is grounded far below sea level. The WAIS rests on bedrock as deep as two kilometers underwater. One 2004 NASA-led study found that most of the glaciers they were studying “flow into floating ice shelves over bedrock up to hundreds of meters deeper than previous estimates, providing exit routes for ice from further inland if ice-sheet collapse is under way.” A 2002 study in Science examined the underwater grounding lines-the points where the ice starts floating. Using satellites, the researchers determined that “bottom melt rates experienced by large outlet glaciers near their grounding lines are far higher than generally assumed.” And that melt rate is positively correlated with ocean temperature.

The warmer it gets, the more unstable WAIS outlet glaciers will become. Since so much of the ice sheet is grounded underwater, rising sea levels may have the effect of lifting the sheets, allowing more-and increasingly warmer-water underneath it, leading to further bottom melting, more ice shelf disintegration, accelerated glacial flow, and further sea level rise, and so on and on, another vicious cycle. The combination of global warming and accelerating sea level rise from Greenland could be the trigger for catastrophic collapse in the WAIS (see, for instance, here).

You can read every thing a laymen could possibly want to know about what the recent study on Antarctic warming does and doesn’t show at RealClimate here.

The authors of the Nature article find:

In Antarctica, we find significant dynamic thinning of fast-flowing ice at rates greater than plausible through interannual accumulation variability for drainage sectors….  On the glacier scale, thinning is strongest in the Amundsen Sea embayment (ASE), where it is confirmed as being localized on the fast-flowing glaciers and their tributaries (Fig. 3 [below]. The area close to the Pine Island Glacier grounding line thinned in the period 2003-2007 at up to 6 m yr-1, neighbouring Smith Glacier thinned at a rate in excess of 9 m yr-1 and Thwaites Glacier thinned at a rate of around 4 m yr-1. These rates are higher than those reported for the 2002-2004 period.

They conclude:

In Antarctica, dynamic thinning has accelerated at the grounding lines of the major glaciers of the Amundsen Sea embayment, and in places has penetrated to within 100 km of the ice divides. Ice-shelf-collapse glaciers show particularly strong thinning that has persisted for years to decades after collapse and in places has penetrated to their headwalls. Although losses are partly offset by strong gains on the spine and western flank of the Antarctic Peninsula, numerous glaciers feeding intact Antarctic Peninsula, West Antarctic and East Antarctic ice shelves are also thinning dynamically. We infer that grounded glaciers and ice streams are responding sensitively not only to ice-shelf collapse but to shelf thinning owing to ocean-driven melting. This is an apparently widespread phenomenon that does not require climate warming sufficient to initiate ice-shelf surface melt. Dynamic thinning of Greenland and Antarctic ice-sheet ocean margins is more sensitive, pervasive, enduring and important than previously realized.

Did I mention the time to act is now!

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21 Responses to Nature: “Dynamic thinning of Greenland and Antarctic ice-sheet ocean margins is more sensitive, pervasive, enduring and important than previously realized”

  1. This is irrelevant to climate issues, but I don’t see how they can talk about East and West Antarctica.

    You can get to any longitude in Antarctica from any other longitude an Antarctica by traveling either east or west. There are no boundaries marking the eastern and western ends, comparable to the Atlantic and Pacific oceans in the the US.

  2. Jay Alt says:

    I assume the units on the color scale, [ ma-1 ] are the annual loss in meters?

  3. We seem to use the phrase “…more than previously realized” more often.

  4. Ethan O'Connor says:

    Jay — yep, that unit reads as “meters per annum”, synonymous with meters per year.

  5. Steve Bloom says:

    Re #1: Think eastern and western hemispheres, Charles. It’s an arbitrary dividing line, but gets used because it happens to line up pretty well with the Trans-Antarctic Range dividing the area occupied by the grounded ice sheet and Peninsula from the larger main ice sheet.

  6. this is…not good news. if .8 degrees C accomplishes this…

    in any event, i guess it makes our point over the weekend at 350.org a little more obvious. many many thanks to all who helped out!

  7. I think it’s obvious that we’re causing the problem by firing so many laser beams at Greenland and Antarctica.

    http://one-blue-marble.com/blog/2009/10/01/epiphany-evil-scientists-are-destroying-the-planet/

    :::This is me trying to be funny again because it’s so easy to get discouraged in this business:::

  8. Wonhyo says:

    “Richard Pauli says:
    October 26, 2009 at 1:33 pm
    We seem to use the phrase “…more than previously realized” more often.”

    In two years of monitoring climate science news, every updated accelerates the predicted schedule for climate change.

    Now when I see a scientific prediction that some climate effect will occur in X number of years, I cut that number in half.

    I used to criticize JR for not advocating stronger action sooner, but now I realize he’s walking a fine line between what’s necessary and what’s politically possibly. I think we need to continue supporting JR’s proposals on the political front, while taking even stronger actions outside of politics. I hope 350.org’s impact grows rapidly beyond yesterday’s event.

  9. So far, no one has published the figures for the 2008-2009 melt season with regard to the Greenland Ice Sheet mass balance loss (they have only published numbers for the area of loss of the outlet glaciers).

    I believe it will be a bit shocking.

    But what are they waiting for?

  10. dhogaza says:

    Since we’re on the subject of ice …

    The denialsphere made a big deal about “arctic sea ice recovery” when this year’s minimum extent turned out to be “only” the 3rd lowest and right on the rather scary trend line for 1979-2009.

    They’re quiet on the issue now, concentrating on “low temperatures in the US!!!!” (again!) instead.

    And furthering our image of denialists being pig-igorant, someone want to tell this turkey that helium is not hot air … is not hot air … is not hot air?

    [JR: I've been thinkning about blogging on the ice situation.]

  11. Michael Y says:

    Hi Joe,

    Sorry, but I don’t know where to send interesting stuff….What looks like a pretty good analysis of CCS in the Alberta Tar Sands (conclusion: uneconomical, insufficient, and too late) just came out.

    http://www.co-operative.coop/Corporate/PDFs/Tar%20Sands%20CCS.pdf

    Michael

  12. ken levenson says:

    #1, As I understand it the East and West ice sheet distinction is of vital importance because the East ice sheet sits on land above sea level and is essentially stable and will be the last ice to melt. But the West ice sheet sits to a significant degree on islands in the water and is the most vulnerable to melting..much more than even Greenland. So they are fundamentally different things.

    I think in rough numbers the ultimate contribution to ocean rise is something on the magnitude of:
    Greenland = 21 feet
    West Antarctic Ice Sheet = 80 feet
    East Antarctic Ice Sheet = 120 feet

    So we can be thankful that the East ice sheet is stable but the West ice sheet will put us underwater much sooner….

    Humanity is in for a very rude awakening.

  13. Another problem for the deniers: The current arctic sea ice measurements show that it is not recovering as rapidly as in the past and that in late October the ice is at the second lowest levels recorded and approaching the 2007 record minimums. See http://www.ijis.iarc.uaf.edu/en/home/seaice_extent.htm

  14. mike roddy says:

    Since the deniers lie like hell, all the time, it’s about time we started responding accordingly. Every claim of theirs can be comprehensively debunked with a link, as in Borenstein’s recent piece about the “cooling” trend. Many of us here have spent plenty of time doing it ourselves.

    Somebody should make up a list of their claims, find and list appropriate tiny urls, and send them to their rooms. Then, instruct them not to come out until they can make a statement that is actually true. Say, a month long timeout, each time. They will have to have a long strategic huddle before coming up with a response to that challenge.

  15. Greg Robie says:

    B. Waterhouse #13,

    I noted this trend too. Over the weekend when I was researching the assumptions used in EPA analysis of CEJAP, I took a break, opened photoshop, and made this composite graph of NSIDC products. Joe, if you do blog on the trends in the ice extent reformation this fall, I hope someone can talk to you about the what may be happening—at least in terms of probabilities. Watching the ice extent decline on a daily basis for two melt seasons now, and looking at older data, this year sure suggested to me that the weather is quickly changing in the Arctic. Is it being discovered that what was known, and could be incorporated into models, is rapidly becoming less and less useful? Like this “surprise” discovery concerning the ice sheets, what else (such as rate of cloud cover increase, changes in the mix of cloud types and composition, precipitation levels and kind of precipitation, etc.) are being observed that is catching the scientists studying the Arctic off guard?

  16. Dorothy says:

    Greg, I don’t think the UK Met Office Hadley Centre is too surprised. On April 5 of this year, sourcing the Met Office, we put up Google Earth Outreach images comparing the temperature anomoly in the Arctic in the winter of 2009 to that of 2010.

    The title of our post is “The Arctic Should Prepare for a Blast of Heat in 2010″ – http://westcoastclimateequity.org/?p=2767

    The graph B. Waterhouse pointed us to regarding the slow recovery of the Arctic sea ice is very unnerving. This isn’t a prediction; it’s actually happening.

  17. dhogaza says:

    The current arctic sea ice measurements show that it is not recovering as rapidly as in the past and that in late October the ice is at the second lowest levels recorded and approaching the 2007 record minimums.

    Yes, good point, which is why I posted it earlier …

  18. Greg Robie says:

    Thanks for the link Dorothy. Do you know if the modeling generating this prediction is based on work like that done in California on a Navy super-computer that predicted and ice free Arctic by 2013 in December of 2007 (I think), and factored in positive feedbacks left out of the last IPCC assessment?

    dhogaza and/or B. Waterhouse, do either of you know anything about the cause of the extended pause in the ice extent reformation in November of 2006 in this graph?

  19. Leland Palmer says:

    This is hard data, from an unimpeachable source, telling an unambiguously threatening message.

    For a truly intelligent species, this would be sufficient evidence, I think.

    But the deniers continue unabated, it seems. Some of them are paid to say what they say, some of them are not.

    Poor Earth, to be stuck with a bunch of half formed monkeys running things.

  20. James Newberry says:

    Based on this information, it seems Western Man has created the atmospheric conditions for the planet to “switch” back to a prehistoric age when there were no planetary ice caps, some thirty million years ago, as I understand. It seems an increase of two C degrees is already in the cards with more heat to “automatically” follow. Remember, today’s CC effects are from carbonic acid gas (CO2) released in past decades.

    I suggest we may see twenty feet of sea level rise in one hundred years if observations continue as they have for several years now.

  21. Lou Grinzo says:

    James: And remember the 40% “bonus” we’ve arbitrarily given ourselves. As David Archer points out in his (excellent) book The Long Thaw, by focusing so narrowly on the year 2100, we’re ignoring the fact that 40% of the warming from CO2 emitted up to that date will happen after 2100.

    I’m shocked that this nasty little detail gets so little attention in online discussions. (Nearly) everyone keeps acting as if 2100 is the finish line–if we get to that year without killing ourselves using climate as a weapon, we’re home free, etc.