I have got complained at for responding to “The impact on the stability of the Greenland ice sheet as well as on global weather patterns would likely be nearly unimaginable” with “…as for the impact on the weather, there is no reason to suppose any problem.” This in the context of the recent loss of Arctic sea ice. So maybe its worth discussing a bit.

The refs for this are the press release containing a pretty pic that is a bit misleading; the Stroeve et al paper that started it; and my somewhat dismissive take.

Stoeve et al get obs trends (for September, ie ice minimum – no-one is suggesting an ice-free *winter* Arctic), in %/decade, of -7.7 (1953-2006); -9.1 (1979-2006) and -17.9 (1995-2006). Using the last figure, you could extrapolate ice-free conditions by 2050. Using the middle one, you’d have to wait till 2100, and the first, even longer. The first figure is bigger than all the model trends, hence the headlines. But its still not very fast. For the faster second and third figures, there are models with higher trends (e.g. for 1995-2006, HadCM3 produces -19.3 and the most extreme of the NCAR CCSM3 ensemble gets -28.3).

Anyway, suppose we suppose an ice free summer Arctic and wonder what this would do to global weather. And I don’t know the answer. You could look in the GCMs, of course, but you;d have a hard time sorting out the sea ice response from everything else. In the absence of any study, and not talking about local effects (it will help the warming of Greenland, for example), I see no reason why it should be bad or good overall. For instance, will it exacerbate or ease the drought in western US? Who knows?

Comments

  1. #1 Ice
    2007/11/20

    hi,
    i was just wondering about that this afternoon…

    maybe this will sound stupid, but wouldn’t it be possible to design an experiment with one 21th century run where you allow the summer sea ice to desappear, and another one where sea ice extent is prescribed each year, so you can roughly tell the differnnce ? (there would be strong inconsistencies i guess, for example between SST and sea ice extent, in the latter, but after all this is also what one does when one prescribes LAI in a climate-carbon run…)

    [Yes, it would certainly be possible to do this. In fact I might well try -W]

  2. #2 John McKay
    2007/11/20

    “I have got complained at…”

    Have you had enough coffee this morning? Your grammar module seems to need rebooting.

  3. #3 crandles
    2007/11/20

    Why are figures for ice obs quoted in terms of %/decade rather than million km^2/decade?

    %/decade implies we will never loose it all. It also makes comparisons more difficult. A much higher %/decade for summer could mean km^2 is falling more slowly than a much lower %/decade figure for winter. Km^2/decade figures are more similar and, at present, more stable than %/decade. Maybe that wasn’t the case in the past when the standard units were decided upon?

    [I assume its % of current values per decade -W]

  4. #4 Steve Bloom
    2007/11/20

    If you take the difference between the 2006 and 2007 minimums and project similar annual losses into the future you get a trend resulting in an ice-free minimum by something like 2011. Not that I would be so bold as to predict such a thing…

  5. #5 Hank Roberts
    2007/11/20

    > I see no reason why it should be bad or good overall

    Ask the marine biologists? As I recall, it’s the algae that forms on and in the sea ice — where it accumulates, held where sun is available and predators are out of reach — that eventually melts out, and provides the nutrients for the zooplankton that live under the ice layer. The change in timing and duration of the sea ice ought to be accompanied by a change in the biology, probably less total food produced during the Arctic summer.

    That’ll be interesting.

  6. #6 Hank Roberts
    2007/11/20

    I don’t know who the biologists are, but they were watching sea ice decline per Dr. Bitz’s model, so they’re out there.

    http://www.realclimate.org/index.php/archives/2007/01/arctic-sea-ice-decline-in-the-21st-century/
    # Cecilia Bitz Says:
    13 January 2007 at 2:24 PM
    … Have I heard from researchers with interest in the ice retreat? I am in contact with several biologists in my universtity and others that I have met in various meetings.

  7. #7 bigTom
    2007/11/20

    I didn’t see anything wrong with the press release, although the Stroeve paper was hiding behind a pay-wall. Since you have a quote about an unimaginable effect of the Greenland Ice cap, I can assume a statement that the lack of sea-ice may massively accellerate its demise. I would consider later statement to be irresponsibly alarmist, although the effect should be simulatable.

    Clearly recent ice history and the models are showing a very significant level of divergence. I doubt anyone has much of a handle on how much (if any) of the divergence is due to decadal time scale natural cycles. I don’t even know if we can tell the differernce between a decadal level natural cycle, and a GW circulation response.

    Personally I suspect neglect of the possible effect of soot on snow/ice albedo might be part of the explaination, but I’m no climate scientist.

  8. #8 Alexander Ač
    2007/11/20

    Aha William,

    Jim Hansen at Scitizen argues that Canadell et al. paper probably misleaded the public, considering the incresing airborne fraction of CO2:
    http://scitizen.com/screens/blogPage/viewBlog/sw_viewBlog.php?idTheme=13&idContribution=1211&PHPSESSID=cff2af9edc2bcef0170f6c67db57293b

    now… did the AF increase or not??? Probably I was midleaded too :-/

    What about Eli Rabett?

  9. #9 Gareth
    2007/11/20

    Yes, it would certainly be possible to do this. In fact I might well try -W

    Sometimes, with enough prodding, curiosity can be stirred…

    From Weather Underground’s new Climate Change section, this feature summarises Masters’ views thusly:

    Continued loss of Arctic sea ice may dramatically change global weather and precipitation patterns in the decades to come. The jet stream will probably move further north in response to warmer temperatures over the pole, which will bring more precipitation to the Arctic. More frequent and intense droughts over the U.S. and other regions of the mid-latitudes may result from this shift in the jet stream. Changes to the course of the jet stream affect weather patterns for the entire planet, and we can expect impacts on the strength of the monsoons and recurvature likelihood of hurricanes. Exactly what these effects might be and what regions would be most strongly affected are difficult to predict. In any case, the reduced Arctic sea ice should give most of the Northern Hemisphere a delayed start to winter this year, and for the forseeable future.

    When thinking about what to look for in the model runs, you might want to read this post by Stu Ostro at the Weather Channel, and download the presentation linked in the text.

    And can we have the results before Christmas, please… ;-)

    [Lots of mays. "More frequent and intense droughts over the U.S. and other regions of the mid-latitudes may result from this shift in the jet stream" - or maybe they'll get less frequent and less intense. Who knows? -W]

  10. #10 Alexander Ač
    2007/11/20

    Oh no,

    One article later over at Scitizen, Ute Schuster argues exactly the opposite:

    “A recent global study by colleagues at UEA together with an international team (Canadell et al., 2007), shows that the fraction of CO2 emission taken up by the oceans has decreased since around 1960. Our result from the North Atlantic verifies this by direct measurements. ”

    but still, nothing is clear:

    “The question is how much the North Atlantic, and the global oceans for that matter, will take up [CO2] in the future. Computer models of ocean uptake vary in their conclusions: from more uptake, to no change in the uptake, to less uptake.”

  11. #11 Alexander Ač
    2007/11/20

    This bring up a question: “Shouldn’t there be a Nobel Prize for communicating the [climate] science”?

  12. #12 Adam
    2007/11/21

    “In any case, the reduced Arctic sea ice should give most of the Northern Hemisphere a delayed start to winter this year, and for the forseeable future.”

    Which is interesting if you look at the temperatures and snow cover (and events) in Europe. But this is probably down to the blocked nature of the system at the moment – what’s causing that is probably a different question.

    I would expect it to change things – there’s a lot of heat exchange during the ice freeze and melt, and the air can be heavily affected by the temperature of the oceans. The whole synoptic set-up can be affected by the temperature differences between air masses and the underlying oceans.

    As to how it affects it is a good question and I’d be interested to know if the models used to predict the shifting of the jet streams included ice extent? If not, it would be interesting to see if someone’s studying what effect reduced ice cover will have. I’d have thought that any change will cause a problem for someone, but if we’re talking balances over the NH (or globe), who knows? I guess we’ll find out eventually.

  13. #13 Frank
    2007/11/21

    What evidence is there to suggest that Greenland is unprecedentedly warmer than in the past? The Greenland ice core proxies show higher temperatures during the Holocene Maximum and the Medieval Warm Period. Those temperatures did not result in the disappearance of the Greenland ice sheet (Largely ice-free Arctic summers must have been highly likely at that time). Extrapolating trends is great fun but seldom leads to accurate predictions.

    [Could be a fair point; e.g. http://www.ncdc.noaa.gov/paleo/pubs/alley2000/alley2000.gif Mind you, you have to be careful about "now". PD is apparently about -31 oC - what is your evidence that it was warmer during the MWP? -W]

  14. #14 John McCormick
    2007/11/21

    Frank, maybe it is too early for me to be thinking straight but I want to know how one makes an accurate prediction. Does it have something to do with perfect hindsight?

    And, William, you said:

    [Lots of mays. "More frequent and intense droughts over the U.S. and other regions of the mid-latitudes may result from this shift in the jet stream" - or maybe they'll get less frequent and less intense. Who knows? -W]

    No one.

    Yet, Western North America is the world’s breadbasket reliant, in part, upon groundwater irrigation from aquifers being heavily mined. Australia is losing about 60% of its wheat crop. China and India are losing crops to drought and desertification.

    Who knows? Scientists should. And, time is running out for answers. The US National Academy of Science spent a year and lots of money to write a report on abrupt climate change. It is an archive.

    Arctic ice meltback IS abrupt climate change and we do not have a clue what that means for food availability when the grain basket is near empty.

  15. #15 David B. Benson
    2007/11/21

    Winter starting fairly normally in the Pacific Northwest this year.

  16. #16 Frank
    2007/11/22

    Thanks for the GISP2 data http://www.ncdc.noaa.gov/paleo/pubs/alley2000/alley2000.gif unfortunately the graph makes identifying small differences in temperature difficult due to the scale, but higher temperatures than today seem to have occurred several times (including the MWP which is shown on graph), although admittedly those temperatures were not much higher than today’s. The key question still remains, are today’s temperatures and their rate of increase unprecedented? I may be missing something, but looking at the graph, I cannot see anything to suggest that they are.

    [That picture doesn't show todays temperatures on it. If you find the bumps hard to see, just knock all past the / off the URL to get to the data -W]