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Antarctic Sea Ice Extent and Area: 1979-2006
Reference
Cavalieri, D.J. and Parkinson, C.L. 2008. Antarctic sea ice variability and trends, 1979-2006. Journal of Geophysical Research 113: 10.1029/2007JC004564.

What was done
In a study that "extends the analyses of the sea ice time series reported by Zwally et al. (2002) from 20 years (1979-1998) to 28 years (1979-2006)," the authors derived new linear trends of Antarctic sea ice extent and area, based on satellite-borne passive microwave radiometer data.

What was learned
Cavalieri and Parkinson report that "the total Antarctic sea ice extent trend increased slightly, from 0.96 0.61% per decade to 1.0 0.4% per decade, from the 20- to 28-year period," noting that the latter trend is significant at the 95% confidence level. Corresponding numbers for the Antarctic sea ice area trend were 1.2 0.7% per decade and 1.2 0.5% per decade. Both sets of results also indicate a "tightening up" of the two relationships.

What it means
Over the last eight years of the study period, both the extent and area of Antarctic sea ice have continued to increase, with the former parameter increasing at a more rapid rate than it did over the 1979-1998 period. As for why this is the case, the two researchers cite the modeling work of Zhang (2007), which points to "reduced convective over-turning in the ocean beneath the ice and hence reduced ocean heat flux available to melt ice, resulting in an overall increase in ice extent and volume." When concluding their paper, however, Cavalieri and Parkinson say that "what is driving the observed changes remains unanswered, and the physical mechanisms explaining these changes remain to be determined."

References
Zhang, J. 2007. Increasing Antarctic sea ice under warming atmospheric and oceanic conditions. Journal of Climate 20: 2515-2529.

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 August 2008