21 July 2011
There was update from the National Snow and Ice Data Center this week regarding the summer melt of Arctic Ocean sea-ice. It’s beginning to look as if a new record low in ice extent is possible by the time the melting ends in early September, passing the all time low set in 2007.
Here is the update from NSIDC:
Overview of conditions
As of July 17, 2011, Arctic sea ice extent was 7.56 million square kilometers (2.92 million square miles), 2.24 million square kilometers (865,000 square miles) below the 1979 to 2000 average. Sea ice is particularly low in the Barents, Kara, and Laptev Seas (the far northern Atlantic region), Hudson Bay and Baffin Bay.
Conditions in context
Arctic sea ice extent declined rapidly through the first two weeks of July, at a rate averaging nearly 120,000 square kilometers (46,000 square miles) per day. Ice extent is now tracking below the year 2007, which saw the record minimum September extent.
During the first half of July, a high-pressure cell persisted over the northern Beaufort Sea, as it did in June, and is linked to the above-average air temperatures over much of the Arctic Ocean. To date in July, air temperatures over the North Pole (at the 925 millibar level, or roughly 1,000 meters or 3,000 feet above the surface) were 6 to 8 degrees Celsius (11 to 14 degrees Fahrenheit) higher than normal..(my highlight)
Low summer snow cover in the Northern Hemisphere
As noted in our May 4 post, snow cover in central Russia retreated early in response to warm conditions this spring. Updated analyses provided by the Global Snow Cover Lab at Rutgers University reveal that snow cover remained very low for May and June. Even though some mountain regions in the U.S. and Canada saw greater-than-normal snow cover, snow cover for the Northern Hemisphere as a whole for May and June was the second lowest since the start of snow cover records in 1966.
According to David Robinson, head of the Rutgers Snow Cover Lab, a new pattern is emerging in which the Northern Hemisphere is cloaked in above-average snow during late autumn, winter, and early spring, followed by rapid melt and retreat in May and June. While snow cover varies from year to year, the far north has seen a clear trend towards less spring snow cover over the last thirty years. (End NSIDC Update)
A collection of forecasts for the yearly low from 15 different science groups is put together by ARCUS, (Arctic Res. Consortium) and the July forecast now has 9 of the 15 forecasting a record low. The reason so many are now indicating a possibility that the melt will pass the record low year of 2007 has to do with a pressure pattern called the Arctic Dipole. This pattern of higher pressure on the North American/Greenland side of the Arctic favors a rapid summer melt and the resulting wind flow exports sea ice out of the Arctic as well.
The Arctic dipole pattern has reemerged for a couple of weeks now, and is a rather recent discovery. This has prompted some researchers to surmise it may be a result of the reduction in sea ice and snow cover over the Northern Hemisphere. If it holds like it did 4 years ago, the summer melt may pass the extreme low of 2007, and will likely solidify the expectations that the Arctic Ocean may be essentially ice-free in just a few decades. A good paper to read on this was published in Geophys. Res. Letters in 2008 and is here. (Thanks to Jeff Masters at Weather Underground for the tip on that paper and an exc. summary of it)
Another independent measurement of the sea ice extent (using the NASA Aqua and TRMM satellites Advanced Microwave Scanning Radiometer) is put together by JAXA. This data is also indicating ice extent running at record low levels for mid July. The total volume of Arctic ice is estimated by the PIOMAS model at the Polar Science Center (Uni. of Wash.). This model has recently been updated and shows a loss of sea ice around 2,800 cubic kilometers/decade.
I write about all kinds of earth science here, but there are a couple of blogs by ice experts out there that are quite good. I’m a remote sensing and Polar fanatic so I read them daily. DOSBAT is a new one, and Meltfactor by Dr. Jason Box is another one. Neven’s Arctic Sea Ice has been in my Google reader for quite some time and is excellent. If you are interested in the real science behind the numbers and how they are derived, you can learn a tremendous amount on those sites.
I want to end with some links to some journal publications for those who want to go very deep into it. (Starting with the most recent.)
Maslanik, J., J. Stroeve, C. Fowler, and W. Emery (2011), Distribution and trends in Arctic sea ice age through spring 2011, Geophys. Res. Lett., 38, L13502, doi:10.1029/2011GL047735.
If you are wondering whether the ice loss is part of a natural cycle, then the answer is that everything from increasing greenhouse gases to natural Ocean/Atmosphere internal cycles play a role in the amount. Some of the past rapid loss is probably to do with the phase of the AMO and a paper just out talks about this (long suspected so not really a surprise). Teasing out the anthropogenic signal from the natural background fluctuations is what makes this branch of science so interesting. The overwhelming scientific evidence/opinion remains that the ice loss is mainly anthropogenic.
Chylek, P., C. K. Folland, H. A. Dijkstra, G. Lesins, and M. K. Dubey (2011), Ice-core data evidence for a prominent near 20 year time-scale of the Atlantic Multidecadal Oscillation, Geophys. Res. Lett., 38, L13704, doi:10.1029/2011GL047501
If you start reading papers about Arctic ice, you will see the name Kwok a lot and you should read his papers- this one from 2009 is a must read.
Kwok, R., G. F. Cunningham, M. Wensnahan, I. Rigor, H. J. Zwally, and D. Yi (2009), Thinning and volume loss of the Arctic Ocean sea ice cover: 2003–2008, J. Geophys. Res., 114, C07005, doi:10.1029/2009JC005312.