The AMS has a Draft statement on climate change, vn 7.0. I found it via RP Sr, who dislikes it, for the obvious reasons: it fails to reflect his hobbyhorses: which are, as ever, downplaying the role of CO2 in favour of land-use changes, aerosols, etc (of course it does mention them, but naturally enough after GHGs). I find his “I reproduce a summary below of findings that have been reached on the weblog Climate Science (http://climatesci.atmos.colostate.edu/main-conclusions/ ) which should be discussed in the AMS Statement.” quite shameless self-promotion. It will be interesting to see if the AMS is convinced. I am prepared to agree that the linking to weather predictions models isn’t quite as strong as they imply, but thats just trivia.

OTOH there are some oddnesses: “In the last fifty years atmospheric CO2 concentration has been increasing at a rate much faster than any rates observed in the geological record for several thousand years.” Geological record? They mean ice cores. And several thousand? They mean hundred thousand. Unless they think the glacial termination changes are comparable, but I don’t think they are.

And in the sea level section: “Moreover, ice sheet modeling and paleoclimatic observations indicate that the melting of the Greenland Ice Sheet will likely cause global sea level to rise meters if warming continues at its present rate through the 21st century.” This too seems odd… the last I saw, Greenlands contribution over the next 100y is much less than a meter. Or… is that a carefully constructed true-but-misleading statement? It can, just about, be read as Greenland will cause meters of SLR, at some point in the far future, if T increases through this century. And that version would be true.

Comments

  1. #1 Eli Rabett
    2006/11/17

    The thing about the ice caps goes like this: To actually melt the ice will take a lot longer than a century, HOWEVER, we are rapidly approaching a point of no return after which the melting becomes inevitable. Unfortunately people do not stress this point. You can see it here a deSmogBlog special.

    [This is true. But once its inevitable its still quite slow, unless something strange happens -W]

  2. #2 Eli Rabett
    2006/11/17

    William this all gives new meaning to apres moi le deluge.

  3. #3 Hank Roberts
    2006/11/17

    I recall one mention some years back that some navies were deploying unmanned submersibles to investigate the area along the edge where the Antarctic grounded ice changes to the floating ice. This isn’t uniform block ice, it’s full of rifts that are full of ‘melange’ — not strong stuff.

    “2005-06 Helen has used ICESat data to study the vertical structure of rifts and the mélange which fills them, revealing that mélange accounts for about 30% of the entire ice shelf thickness (Fricker et al., 2005c; Figure 1). Ice shelf rifts are the subject of a SIO-led International Polar Year (2006-08) project CRAC: Collaborative Research into Antarctic Calving.
    ….
    “…ICESat can “see” the tide-forced flexure zone between fully grounded
    continental ice and fully floating ice shelf ice, identifying the landward and seaward limits of ice flexure, providing accurate GZ location and width information for each track …”
    http://www.igpp.ucsd.edu/PDF/research/2006/IGPP_Annual_Report_2006_lo.pdf.

    and

    “We are just beginning to run submersibles under the ice shelf
    – the United Kingdom has in fact this year lost one under the ice shelf …”
    http://sea.unep-wcmc.org/resources/PDFs/EnvtonEdge04-05LR.pdf. at p45

    And we’re staying blind.
    Triana’s in the warehouse; Cryosat didn’t reach orbit
    … “Cryosat was supposed to examine the effects of global warming on the polar ice caps….”
    http://www.theregister.co.uk/2005/10/08/cryosat_crashes_and_burns/

    Hard to imagine not being a bit surprised there — there would have to be unpredictable events when high tides and storm surges slightly change the buoyancy of the grounded ice, changing a band from being grounded to floating, say.

    That edge is the fulcrum. The lever would be all the floating ice seaward of that band being lifted slightly and evenly. I’d imagine a bit of cracking would occur each time.

    On a nearly flat slope a millimeter of lift might mean a change from grounded contact to floating of a meter laterally, lifting that bit of ice, allowing slight cracking, maybe opening a bit of a gap so meltwater could begin to penetrate and drain out at low tide, further widening any breaks.

    “The sudden appearance of thousands of small icebergs suggests that the shelves are essentially broken up in place and then flushed out by storms or currents afterward.”
    http://www.sciencedaily.com/releases/1999/04/990409073216.htm

    and

    October 4, 2006
    “… storm in Alaska last October generated an ocean swell that broke apart a giant iceberg near Antarctica six days later … said Douglas MacAyeal of the University of Chicago and Emile Okal at Northwestern University.”

    Perhaps living in earthquake country makes this sort of creep and crack seem less unlikely to me. They keep finding surprises about earthquakes too.

    [Sorry this too a while to appear. I've been on hols. We lost an autosub under the ice, but I don't think the navy were involved.

    As to being a mechanism for SLR - my instinctive reaction is doubt, because tidal and storm flexures are already much larger than 0.5 m - W]

  4. #4 coby
    2006/11/18

    “unless something strange happens”

    like meltwater penetrating all the way to the bottom of the ice sheet causing melting from the bottom and lubricating the inevitable slide to the sea?

    Does anyone have a lot of confidence in the ice sheet models?

  5. #5 Kooiti Masuda
    2006/11/18

    I guess that “several thousand years” means just the Holocene, for it is not very certain whether the rate at the end of the Younger Dryas is smaller than the current rate.

    [I would have said it was faster now: see, e.g., http://en.wikipedia.org/wiki/Image:Carbon_Dioxide_400kyr.png -W]

    I feel “geological” odd too. Perhaps the drafter wanted to mention ice cores and really geological evidence together. And in someone’s mind glaciology is part of geology, but probably in no one’s mind geology is part of glaciology. Inconveniently, the term “proxy” does not seem appropriate here, since the evaluation of concentration from bubbles is nearly direct, though other geological estimates are aptly called proxies.

    I find that the section “Why is climate changing?” is confusing about the role of water vapor. Water vapor is mentioned as one of greenhouse gases, and novice readers would not know that the numbers shown as “the greenhouse gas contribution to warming” do not explicitly take contribution of water vapor into account. It seems better to discuss “forcing” and maybe “feedback” here. Perhaps the drafter of this part wanted to avoid introducing more technical terms. But these words are actually used in later sections without definition.

    [I didn't think that was so bad. They probably feel obliged to mention WV, but at least they list it last - W]

    Ko-1 M. (Kooiti Masuda)

  6. #6 Hank Roberts
    2006/11/18

    I tried a longer posting yesterday that hasn’t showed up, with excerpts and some links on current ice sheet work yesterday.

    I’d speculated that slight increase in sea level means slight increase in leverage — the floating ice as the lever, the line between grounded and floating ice as the fulcrum, and the cracking would occur there both from slightly greater lifting, both from tides and from storm waves, at peak sea heights.

    Then I went to Google, of course (grin), to validate my speculation.
    Posting that and awaiting correction from real scientists, as always.

    From this: http://sea.unep-wcmc.org/resources/PDFs/EnvtonEdge04-05LR.pdf.

    “We are just beginning to run submersibles under the ice shelf – the United Kingdom has in fact this year lost one under the ice shelf…”
    [They had high hopes for Cryosat, which failed to reach orbit]

    From http://www.igpp.ucsd.edu/PDF/research/2006/IGPP_Annual_Report_2006_lo.pdf.

    “Ice shelf rifting: In 2005-06 … study rifts at the front of the ice shelves. … little is known about the processes involved in rift propagation, and we do not know how these processes will respond to climate change. …. (see http://eqinfo.ucsd.edu/helen/amery_rift. … time series… showing that propagation is faster in the summer than in winter (Fricker et al., 2005a). …. rift propagation is episodic and occurs in discrete events separated by approximately 2 weeks.

    “… used ICESat data to study the vertical structure of rifts and the mélange which fills them, revealing that mélange accounts for about 30% of the entire ice shelf thickness (Fricker et al., 2005c; Figure 1). …

    “… In 2005-06, Helen has also used ICESat data to map the grounding zones of the ice shelves – the dynamically-active transition zones between grounded and floating ice. ICESat can “see” the tide-forced flexure zone between fully grounded continental ice and fully floating ice shelf ice, identifying the landward and seaward limits of ice flexure …..”

    So my hunch is that the slight increase in ocean elevation, at peaks (two week intervals? Is that peak lunar tides?) is able to exert a new, slightly greater than before, lifting force, lift the grounded ice along the edge (a millimeter of lift on a flat slope would be a meter laterally of separation, waving hands wildly ….) — let water in, let cracks melt out a bit to connect the surface melt to the base of the ice. “Melange” is crunched up ice/air/water, and thirty percent means the ice is loosely consolidated, without much strength laterally.

    Earlier links noted that floating ice has come apart rapidly, indicating it just fell apart.

    From a 1999 news story at http://www.sciencedaily.com/releases/1999/04/990409073216.htm

    “The sudden appearance of thousands of small icebergs suggests that the shelves are essentially broken up in place and then flushed out by storms or currents afterward.”

    “The British Antarctic Survey scientists had predicted one of these retreats, using computer models to demonstrate that the Larsen B was nearing its stability limit. With the small breakup observed last spring, the shelf had already retreated too far to continue to be supported by adjacent islands and shorelines.

    “Scientists at both institutes expected the two shelves to fail soon, but the current disintegration is occurring at an even faster rate than earlier breakups gave reason to anticipate. ”

  7. #7 Luboš Motl
    2006/11/18

    What does American Mathematical Society have to do with these climate questions? Or does AMS stand for some crackpots who just try to steal the mathematicians’ trademark? ;-)

  8. #8 Hank Roberts
    2006/11/18

    > … meters of SLR …
    Perhaps their meters go to 11?

    Just checking if a short post will show up, since my long ones about antarctic ice rifts aren’t appearing.

  9. #9 Stephen Berg
    2006/11/18

    Lubos, the AMS stands for the American Meteorological Society.

  10. #10 Hank Roberts
    2006/11/18

    http://scrippsnews.ucsd.edu/article_detail.cfm?article_num=685

    “… details of ice shelf “rifting”-ice fracturing that cuts through the entire thickness of an ice shelf and represents the first stage of the process in which icebergs eventually break away from the main ice mass-on East Antarctica’s Amery Ice Shelf.”

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