Arctic sea ice maximum and minimum in 2011. From NASA: “These Arctic sea ice images represent real data captured by the AMSR-E instrument aboard NASA’s Aqua satellite. The top image is from Mar. 7, 2011, when sea ice reached its maximum extent this year, near the end of winter. The bottom image is from Sept. 9, 2011, around the time sea ice reached its minimum extent this year, near the end of summer. Both extent and thickness of Arctic sea ice remains in a long-term decline, correlated with rising global surface temperatures.” ( NASA )

NOAA announced today that August was globally the eighth warmest on record, about one degree above the 20th century average. It also reported the June through August period was 7th warmest on record. June through August temperatures have been warmer than average across the globe for 35 straight years (since 1976).

Meanwhile, the National Snow and Ice Data Center (NSIDC) made the preliminary announcement that Arctic ice “appears to have reached its lowest extent for the year.” On September 9, Arctic sea ice extent fell to 4.33 million square kilometers, about 2 million square kilometers below average, second only in minimum extent to 2007 in the satellite record (1979 to present).

Temperatures in August relative to average across the globe. (NOAA)

NSIDC emphasized the preliminary nature of this announcement, noting “changing winds could still push ice flows together, reducing ice extent further.” It may not be possible to confidently declare a minimum until early October.

Furthermore, as I posted yesterday, while NSIDC’s estimate of the minimum extent is second lowest on record, some instruments/algorithms are suggesting a new record low. And University of Washington’s estimate for Arctic sea ice volume - which takes into account the ice thickness - is lowest on record.

The excellent Sea Ice Blog writes:

If we look at the six most important data sets - which IMHO [in my humble opinion] are IJIS [Japan Aerospace Exploration Agency] extent, NSIDC extent, Cryosphere Today area, University of Bremen extent, DMI [Danish Meteorological Institute] extent and PIOMAS [University of Washington] volume - we see that this year a new record has been reached in three of them [Cryosphere today, University of Bremen, and PIOMAS].

In addition,this blog provides a nice summary of the evolution of the melt season relative to past years:

2011 had a flying start to the season, pretty much like 2010. But where 2010 came to a standstill around July 1st due to a dramatic switch in weather patterns, 2011 continued melting at a brisk pace for two weeks longer. A similar switch in weather patterns then slowed things down considerably...

2011 recovered somewhat in August, but some very bad weather for extent and area decrease cut the season short abruptly (2010 had better luck with some weather patterns that extended the melting season and took it into third position in all data sets), much shorter than most recent years.

Where 2007 had an absolute perfect melting season, 2011 had some severe hiccups in the final 8 weeks of the melting season. Despite all of this 2011 beat 2007 on some of the graphs, and came within spitting distance on others.

The bottom line here is that the summer was very warm globally (and in the Northern Hemisphere), and Arctic sea ice continues its long-term decline.