The National Snow and Ice Data Center’s reported this week:
Arctic sea ice extent for June 2011 was the second lowest in the satellite data record since 1979, continuing the trend of declining summer ice cover. Average ice extent fell below that for June 2007, which had the lowest minimum ice extent at the end of summer. However, ice extent this year was greater than in June 2010. The sea ice has entered a critical period of the melt season: weather over the next few weeks will determine whether the Arctic sea ice cover will again approach record lows.
Whatever happens in the short-term, the long-term trend in sea ice extent is unmistakable:
Monthly June ice extent for 1979 to 2011 shows a decline of 3.6% per decade.
Extent is, however, just a two-dimensional measure of how Arctic sea ice is trending. We know that the third dimension — thickness — has also been melting away (see “Arctic sea ice volume: The death spiral continues; One-year-old ice in Beaufort Sea now a foot thinner than in 2009″).
The best modeling of Arctic sea ice volume is done by the Polar Science Center of the Applied Physics Laboratory at the University of Washington. They have recently improved their PIOMAS model using the best observational data — and they have released their data for others to analyze. They have also added ‘conservative’ error bars to their estimates. Finally, they just published their reanalysis in the Journal of Geophysical Research, “Uncertainty in Modeled Arctic Sea Ice Volume.”
Their key conclusion is that the death spiral of Arctic sea ice continues:
… the 2010 September ice volume anomaly did in fact exceed the previous 2007 minimum by a large enough margin to establish a statistically significant new record.
So those who have been asserting that the Arctic is in some sort of recovery are wrong. Quite the reverse.
Here is PSC’s improved 30-year trend-line for the reduction in volume:
Daily Sea Ice volume anomalies for each day are computed relative to the 1979 to 2010 average for that day of the year.
PSC reports, “Monthly averaged ice volume for June 2011 was 15,700 km3. This value is 37% lower than the mean over this period, 47% lower than the maximum in 1979, and 2.5 standard deviations below the trend. Shaded areas represent one and two standard deviations of the residuals of the anomaly from the trend.”
Neven’s Arctic Sea Ice Blog — a must for cryo-junkies — has some excellent charts based on the PSC data
Wipneus made a graph that shows all the trends in the period 2002-2011:
This year’s volume is just below last year’s.
And here’s the monthly average with exponential trend
Whether the trend will actually turn out to be exponential or not remains to be seen.
In November, Rear Admiral David Titley, the Oceanographer of the Navy, testified that “the volume of ice as of last September has never been lower” in the last several thousand years.” Titley, who is also the Director of Navy’s Task Force Climate Change, said he has told the Chief of Naval Operations that “we expect to see four weeks of basically ice free conditions in the mid to late 2030s.”
Wieslaw Maslowski of the Naval Postgraduate School has “projected a (virtually) ice-free fall by 2016 (+/- 3 yrs).” Contrary to some reporting, that projection has been unchanged for years, though Maslowski is in the process of creating a more sophisticated model that he expects “will improve prediction of sea ice melt,” as he explained to me recently.
Tamino also has an excellent analysis of all of the PIOMAS data. As he concludes:
The phrase “death spiral” comes to mind.