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Update on Remotely-Sensed Antarctic Sea Ice Extent
Pezza, A.B., Rashid, H.A. and Simmonds, I. 2012. Climate links and recent extremes in Antarctic sea ice, high-latitude cyclones, Southern Annular Mode and ENSO. Climate Dynamics 38: 57-73.

The authors say that in the Southern Hemisphere there has been a modest increasing trend in sea ice extent (SIE) around Antarctica over the era of satellite coverage, citing the studies of Watkins and Simmonds (2000), Zwally et al. (2002), Parkinson (2004), Turner et al. (2007) and Comiso and Nishio (2008).

What was done
In their broader study of the climatic link between the Southern Annular Mode and Southern Hemisphere SIE, Pezza et al. derived a history of Antarctic SIE for the period stretching from autumn 1979 to autumn 2008, based on remotely-sensed Nimbus-7 SMMR and DMSP SSM/I passive microwave data from the National Aeronautics and Space Administration's National Snow and Ice Data Center.

What was learned
The three Australian scientists report that modest positive SIE trends were observed during all seasons, noting that "the absolute trends over spring and autumn are the most pronounced, with an increase of about half a million square kilometers over the whole period." In percentage terms, they say "there is an increase between 2 and 3% during winter and spring and from 5 to 7% during the low ice season." Of special note is their finding that "the greatest SIE on record observed during the low sea ice season occurred repeatedly in December 2007-February 2008 and March-May2008," with both records being "far greater" than all previous records: 6% greater in the first case and 8% greater in the second.

What it means
Noting that "southern sea ice has shown modest increases and established new record ice coverage in the summer of 2008 by a wide margin," Pezza et al. conclude their study by rhetorically wondering how this "peculiar behavior" meshes with the theory of currently-unprecedented anthropogenic-CO2-induced global warming.

Comiso, J.C. and Nishio, F. 2008. Trends in the sea ice cover using enhanced and compatible AMSR-E, SSM/I, and SMMR data. Journal of Geophysical Research 113: 10.1029/2007JC004257.

Parkinson, C.L. 2004. Southern Ocean sea ice and its wider linkages: insights revealed from models and observations. Antarctic Science 16: 387-400.

Turner, J., Overland, J.E. and Walsh, J.E. 2007. An Arctic and Antarctic perspective on recent climate change. International Journal of Climatology 27: 277-293.

Watkins, A.B. and Simmonds, I. 2000. Current trends in Antarctic sea ice: the 1990s impact on a short climatology. Journal of Climate 13: 4441-4451.

Zwally, H.J., Comiso, J.C., Parkinson, C.L., Cavalieri, D.J. and Gloersen, P. 2002. Variability of Antarctic sea ice 1979-1998. Journal of Geophysical Research 107: 10.1029/2000JC000733.

Reviewed 20 June 2012