AGU meeting: The outlook for the Arctic
American Geophysical Union meeting, San Francisco -
News from the Arctic just continues to get worse. A fair number of presentations here have been dealing with the dire 2007 conditions for sea ice and the Greenland ice sheet.
First up, Greenland. Last summer, more ice melted atop Greenland than ever before measured, adding to a consistent downward trend of some 135 gigatons of ice disappearing per year. Marco Tedesco, of the Goddard Space Flight Center in Maryland, told the meeting that surface temperatures in Greenland were four to six degrees Celsius warmer than usual this summer, which helped accelerate melting, particularly at high latitudes.
The situation is even more precarious for sea ice. A couple of researchers here have been tossing around dates like 2012 or 2014 for estimates of when the Arctic might be completely ice-free in summer. While these sorts of numbers are pretty arm-waving at the moment (numbers like 2040 were previously considered to be aggressive), there’s little reason to think the situation will get better in the next couple of years. Mark Serreze, of the University of Colorado, spent a keynote lecture on Tuesday showing images of Arctic ice shrinking like a snowman left out too long in the sun. In September of this year, sea ice covered just 4.2 million square kilometers - by far the lowest record ever.
And the ice isn’t only shrinking in extent – it’s also thinning. Don Perovich, of a US army cold regions and research laboratory in New Hampshire, reported on a single but extraordinary ice buoy in the Beaufort Sea. In June the buoy measured sea ice at that location as 3.3 metres thick – “really a healthy piece of ice,” as he put it. But by the end of the summer, 70 centimetres had melted off the top – and 2.2 metres (yes, metres) off the bottom.
When you see those dramatic maps of the Arctic ice extent shrinking over time, don’t forget that it’s also thinning – a complicating factor that may just make things worse in summers to come.
Cross-posted from Alex Witze on In the Field
Comments
There's nothing arm-waving about the 2013 result (AGU abstract pasted below). Maslowski (a respected researcher who's the U.S. Navy's sea ice modeler) was quoted in the press this week as saying that the fundamental problem with the other models is they aren't fine-grained enough to properly show the influx of warm water into the Arctic Ocean. He also noted that he used data only through 2004, which means his results are conservative since they don't incorporate the sharp drop from 2005 through 2007. Also, other results announced at AGU (although as yet unpublished) were that Arctic sea ice volume has been cut in half since 2004. Finally, the NCAR model at least (IIRC the one Serreze uses) does show a sharp drop of the sort seen this summer, but the most recent published result had it happening in 2020. That alone places its projection of an initial ice-free summer in 2040 on very shaky ground. Serreze himself was quoted as saying 2030 now seems more like it, but I don't think he got that from a model. So if there's arm-waving going on, can we say it's by the whole field other than Maslowski's team?
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C22A-06
Understanding Recent Variability in the Arctic Sea Ice Thickness and Volume - Synthesis of Model Results and Observations
Whelan, J (jwhelan@nps.edu), Naval Postgraduate School, Department of Oceanography 833 Dyer Road, Monterey, CA 93943, United States * Maslowski, W (maslowsk@nps.edu), Naval Postgraduate School, Department of Oceanography 833 Dyer Road, Monterey, CA 93943, United States Clement Kinney, J L (jlclemen@nps.edu), Naval Postgraduate School, Department of Oceanography 833 Dyer Road, Monterey, CA 93943, United States Jakacki, J (jjakacki@iopan.gda.pl), Institute of Oceanology, Polish Academy of Sciences 55 Powstancow Warszawy, Sopot, 81-712, Poland
We examine the diminishing sea ice thickness trend in the Arctic Ocean using results from the NPS 1/12-degree pan-Arctic coupled ice-ocean model. While many previous studies have analyzed changes in ice extent and concentration, this research focuses on ice thickness as it gives a better indication of ice volume variability. The skill of the model is evaluated by comparing its ice thickness output to actual sea ice thickness data gathered during the last three decades. This includes the model comparison against the most recently released collection of Arctic ice draft measurements conducted by U.S. Navy submarines between 1979 and 2000. Our model indicates an accelerated thinning trend in Arctic sea ice during the last decade. This trend is robust and independent of timescales for surface temperature and salinity relaxation. The validation of model output with submarine upward-looking sonar data supports this result. This lends credence to the postulation that the Arctic is likely to be ice-free during the summer in the near future.
Posted by: Steve Bloom | December 15, 2007 01:33 AM