On Tuesday NASA and the NSIDC have jointly released a summery of observations of the Arctic melting season of 2011. Although officially both institutes speak of a second lowest sea ice extent, they actually confirm what scientists of the University of Bremen stated, namely that during the September minimum even the ‘historic’ 2007 melting record has been broken. The difference depends on satellite resolution – the Germans use a higher one – so probably they know best.

While the sea ice extent did not dip below the 2007 record, the sea ice area as measured by the microwave radiometer on NASA’s Aqua satellite did drop slightly lower than 2007 levels for about 10 days in early September, explains Joey Comiso, of NASA’s Goddard Institute for Space Studies [GISS – the institute with the best Earth temperature dataset].

[Open water with just 15 percent of floating ice debris, still counts as sea ice extent – not as area though.]

Of course in the end, we’re mainly concerned about the trend. The September months of the last five years – 2007, 2008, 2009, 2010 and 2011 – have brought the 5 smallest sea ice extents in the satellite record.

Below is a nice visualisation by NASA of the actual satellite observations of the Arctic melting season, which starts in March and ends in September each year. Although the world looks pretty frosty at the end of the northern hemisphere winter, we should remember that’s how it is supposed to look up north.

The white world that the movie starts with in fact shows an Arctic Ocean that had just reached the lowest sea ice maximum on satellite record – to take another important trend reference point.

Tom Wagner, NASA’s Cryosphere Program Manager, explains what happened during the Arctic melting season of 2011, why the polar sea ice is important to the global climate and what is causing it to melt.

© Rolf Schuttenhelm | www.bitsofscience.org