Wednesday, September 09, 2009

Arctic sea ice extent declined less this year in August due to... wind

The National Snow and Ice Data Center reported in its Arctic Sea Ice News dated September 8, 2009 entitled "Winds cause sea ice to spread in August" that although the Arctic sea ice extent is still greater than at this point in the season in 2007 and 2008, the greater extent is at least somewhat due to winds. The report says:

Atmospheric circulation patterns in August helped spread out sea ice, slowing ice loss in most regions of the Arctic.

They do not say how large an effect the winds were or what the equivalent extent would have been with normal winds or "Atmospheric circulation patterns."

I had expected the minumum ice extent to be reached within a week, but the report says "NSIDC scientists expect to see the minimum ice extent for the year in the next few weeks." Another part of the report says that there are "one to two weeks left in the melt season" and "The minimum ice extent for the year will probably occur in the next two weeks."

The Arctic sea ice extent didn't some close to a new record, but for August it came in at #3:

While this year's minimum ice extent will probably not reach the record low of 2007, it remains well below normal: average ice extent for August 2009 was the third-lowest in the satellite record. Ice extent has now fallen below the 2005 minimum, previously the third-lowest extent in the satellite record.

The report says that sea ice extent for August 2009 averaged 2.42 million square miles, which is 350,000 square miles more than the record low for August in 2007 and compares to 2.43 million square miles in August of 2005, and is 540,000 square miles below the 1979 to 2000 average.

The way I read this is that the weather pattern in 2007 did some very serious damage and that a fairly substantial portion of that damage has already been recovered. Whether damage comparable to 2007 recurs is entirely speculation, but at least such damage did not recur in either 2008 or 2009.

The report closes by mentioning some new papers:

Three papers published in the past month have added important insight to our understanding of Arctic warming and sea ice decline. Elizabeth Hunke and Cecilia Bitz show that improved models can now reproduce the changes in sea ice extent and sea ice age that have occurred in the last 30 years. Ron Kwok and Drew Rothrock combine satellite data and submarine measurements to show an astonishing decline in sea ice thickness over the last 50 years. And Darrell Kaufman and colleagues show that recent warming has reversed a 2000-year cooling trend in the Arctic, and that this cooling was what would be expected from slow changes in Earth's orbit. The recent changes cannot be explained by these natural factors.

So, in addition to area (extent), we now need to track winds and ice thickness. I appreciate that the science is difficult and that the priorities of the variables can change over time, but it is unfortunate that the scientists have not had a consistent story about what variables to focus on. I hadn't heard wind mentioned until this report and none of the graphics factor in or adjust for that variable, or for ice thickness. Hopefully the official graphics will be updated with these new variables in the near future.

This was certainly not a great month or summer by historical standards, but at least it is a move in the direction counter to the wild claim made two years ago (and last week by Senator John Kerry) that the Arctic would be ice-free in 2013.

I would note that even before these "winds" in August, the extent was still reasonably above the extent in July of 2007. I would say that we should wait a good five years to determine how to properly judge 2007 in context, especially to answer the question of whether it was mostly due to weather fluctuations or climate change.

-- Jack Krupansky

1 Comments:

At 7:58 AM , Anonymous Juliette said...

"it is unfortunate that the scientists have not had a consistent story about what variables to focus on. I hadn't heard wind mentioned until this report and none of the graphics factor in or adjust for that variable, or for ice thickness.

Well, look at the press release from 2007: http://nsidc.org/news/press/2007_seaiceminimum/20071001_pressrelease.html
"At the same time, the pattern of winds pumped warm air into the region. While the warm winds fostered further melt, they also helped push ice away from the Siberian shore."

Be careful to make the difference between weather patterns like winds which influence the ice differently every year, and the long term trends which clearly show the extent to decline over the course of the past 30 years.

 

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