Ice bottom blues

By Gareth Renowden 19/09/2012


According to the latest bulletin from the National Snow and Ice Data Center in the US, Arctic sea ice is likely to be at or about its minimum extent for the summer (as of Sept 17th). The animation above shows how the ice melt proceeded through the summer (up to Sept 14th), and the graph below shows the extent as of Sept 17th — 3.41 million square kilometres (1.32 million square miles).

NSIDCseaice20120917

The NSIDC notes:

The current extent is 760,000 square kilometres (293,000 square miles) below the previous record minimum extent in the satellite record (4.17 million square kilometres or 1.61 million square miles) which occurred on September 18, 2007. This difference is larger than the size of the state of Texas. The ice extent currently tracks nearly 50% below the 1979 to 2000 average minimum extent.

For an insight into what the ice is really like, I recommend Julienne Stroeve’s blog of her trip on the Greenpeace vessel Arctic Sunrise. This is from her most recent entry (Sept 17th):

I have been surprised by the vast expanses of open water that we came upon after entering the ice. The average ice concentration of the last five days has been about 65 percent, with about 36 percent of that ice being first-year ice, 14 percent being multiyear ice and 10 percent being brash ice (small broken ice floes). Air temperatures have been above freezing, even at 82.82N, 15.16E, so that there have been no new ice formation observed the last five days.

Viewers and listeners to the last Climate Show (and my Radio Ecoshock interview before it) will know something of my thinking on what all this portends, but I’ll have a post pulling it all together once the minimum is finally called.

Elsewhere in the Arctic, this year’s Petermann ice island is motoring south down Nares Strait, as this NASA Earth Observatory image shows.

PetermannEO2012257

To get an idea just how big this lump of ice is, note that the scale bar in the bottom right of the image is 100 kilometres. It’s big.

Meanwhile, professor Peter Wadhams, head of the Polar Ocean Physics Group at Cambridge, has told the Guardian that he expects the Arctic to be ice-free1 means in summer (Aug/Sept) within four years. Given this summer, I can’t say that I find much to disagree with in his prognosis.

This is not good news.

[Update Sept 20th: NSIDC calls minimum at 3.41 m km2. Good NASA article with excellent graphics here.]

[Eric Neasden]

  1. Most people define “ice-free” to be 1 million km2 remaining — the thick ice close to the Canadian archipelago — but it’s not clear from the Guardian if this is how Wadhams defines it.