Sea Ice reaches second lowest minimum extent in 2008

Despite the familiarity of this headline, it actually only became news today (and is still a little uncertain).

The National Snow and Ice Data Centre is today anouncing the sea ice in the Arctic Ocean has reached its minimum extent for this year.

Some notable facts from the article:

• this is the second-lowest minimum extent since at least 1979, when satellite observations became available
• the area is now 2.24 million km^2 below the 1979-2000 average summer minimum
• this year did not set a new record, (congratulations Stoat!) stopping at 9.4% more than the record-setting 2007 minimum
• this measurement reinforces the downward trend observed over the last decades, and is well below that trend line
• this minimum was reached despite overall cooler summer temperatures

What this observation does not mean, despite what the sceptic voices are claiming and will continue to claim, is that arctic ice is recovering. There is considerable natural variation in the year to year melting and refreezing of this polar icecap, and this natural variation is larger than any such myopic view of the long term trend. This means that despite the clear and continuing downward tack of the data, we should not expect to see a new record set each and every year. The fact that 2007's record minimum defeated one set only 2 years previously is very remarkable, and the fact that this year also beat that same once-record minimum is similarily very remarkable.

Sea ice extent is defined as that area of the ocean that is at least 15% covered in ice. As I noted in a previous article, extent is not the only factor in the volume of ice at the north pole. Thickness needs to be factored in as well, and average thickness too is declining.

Just to seal the point on inter annual variability and where this year's measurement fits in I offer this graphic, also from the NSIDC.