Saturday, September 19, 2015

NSIDC Called It - We Passed Minimum Arctic Ice Extent

NSIDC declared on September 15th that the Arctic sea ice extent had passed the annual minimum. I was a little hesitant about this because, while the open water way to the north was freezing, there was still some melting going on along the edges. Now, the ice extent is growing even along the edges, so it is safe to say NSIDC was correct (no real surprise).

This year's Arctic sea ice extent was the fourth lowest ever recorded and was 4.413 million square kilometers (mskm) on September 13. The three lower extents occurred in 2012 (3.387 mskm), 2007 (4.154 mskm) and 2011 (4.344 mskm). In comparison, this was a 12.7% drop from 2013 (5.055 mskm) and a 12.3% drop from 2014 (5.036 mskm). 

The trend of declining sea ice is unmistakable. This year's sea ice extent passed the lowest minimum for the entire 1980s (6.426 mskm on 9/16/84) by August 8th. It had passed the lowest minimum for the entire 1990s  (5.757 mskm on 9/13/99) on by August 17th. With the exception of 2007, it passed the lowest minimum of every year of the 2000s (4.586 mskm on 9/20/2008) by September 2.

What was particularly disturbing about this year's minimum is that there were no major storms in the region to break up the ice. Long waves and heavy seas will break the ice up into smaller pieces, increasing the surface area exposed to the ocean water and increasing the melt rate. But, that didn't occur this year. This year's melting occurred principally as a combined exposure to a warmer atmosphere, resulting in melting from above, and a warmer ocean, resulting in melting from below. Hopefully, this is not an indicator of things to come, but I don't really see much chance of any alternative.

Here's a plot of this years minimum extent. (The light blue line marks the 1979-2000 average extent.):

Source: CCI

There are now places that use to see it ice over every year, but have not seen ice in as many as 30 years.

The ice volume is a little more difficult to measure. The Polar Portal showed this for the ice volume of the last few years.

Source: Polar Portal
Their models showed the ice volume to be significantly less than in either 2013 or 2014 and with only 2011 and 2012 being lower. Most notably, they show a minimum volume of about 6000 km^3. The Pan-Arctic Ice Ocean Modeling and Assimilation System (PIOMAS) reports ice volume is decreasing at a rate of 3000 km^3 per decade. At that rate, we will have our first ice free Arctic summer within 20 years.

No matter what anyone says, the Arctic sea is is not experiencing a 'recovery.' 

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