The IPCC states that: “Antarctic sea ice continues to show interannual variability and localized changes but no statistically significant average trends, consistent with the lack of warming reflected in atmospheric temperatures averaged across the region”. (AR4 WG1 SPM p.9)
This false claim is repeated in Chapter 4 of WG1, on p 376 ("The antarctic sea ice extent exhibits no significant trend") and on p 351 ("the antarctic results show a small positive trend of 5.6 ± 9.2 × 103 km2 yr–1 (0.47 ± 0.8% per decade), which is not statistically significant.")
In fact, Antarctic sea ice has gradually increased since 1978, as shown by data from The National Snow and Ice Data Center:
See also the graph at Cryosphere Today.
Several published papers confirm this increase in Antarctic sea ice, and that the trend is statistically significant, showing that the IPCC claim is false.
Cavalieri et al, Geophys. Res. Lett. 30, 1970 (2003): Antarctic sea ice has gradually increased since 1977 (following a drop in the early 1970s).
Hanna and Bamber, Derivation and optimization of a new Antarctic sea-ice record, Int J Remote Sensing 22, 113-139 (2003), using satellite data, obtain an increase in Antarctic sea ice extent of 3% over the period 1987-1997.
Vyas et al, On the secular trends in sea ice extent over the antarctic region based on OCEANSAT-1 MSMR observations, Int. J. Remote Sensing 24, 2277-2287 (2003), found a positive trend in Antarctic sea ice and found that this trend is increasing.
Zwally et al, Variability of Antarctic sea ice 1979-1998 J. Geophys. Res. 107, C000733 (2002), found a net increase of both the extent and area of Antarctic sea ice, at a rate of around 1% per decade, and found that this increase was statistically significant.
Remarkably, none of these four papers are cited by AR4 chapter 4, even though that chapter has a section (4.4) on changes in sea ice. The AR4 authors chose to ignore all these peer-reviewed journal articles and instead refer to a book chapter by Comiso which finds a much smaller rate of increase (about 0.5% per decade). By a strange coincidence, the cited author Comiso happens to one of the authors of AR4 chapter 4, while the uncited authors listed above are not.
The very latest research (not available to the IPCC at the time AR4 was written) confirms these results and confirms that the IPCC statements are wrong:
Cavalieri and Parkinson, Antarctic sea ice variability and trends, 1979–2006, J. Geophys. Res. 113, C07004 (2008), find a sea ice extent trend of 1% per decade, and also a slight increase in this trend.
Comiso and Nishio, Trends in the sea ice cover using enhanced and compatible AMSR-E, SSM/I, and SMMR data, J. Geophys. Res. 113, CO2S07 (2008) find a significant positive trend in sea ice area and extent.
Turner et al, Non-annular atmospheric circulation change induced by stratospheric ozone depletion and its role in the recent increase of Antarctic sea ice extent, Geophys. Res. Lett., in press (2009) "demonstrate that the annual mean extent of Antarctic sea ice has increased at a statistically significant rate of 0.97% dec-1 since the late 1970s".
Also, the latest data from NCDC confirms the increase, with a higher trend for southern hemisphere sea ice extent of 2.5% per decade.
Update March 2010: Chip Knappenberger has written an interesting and detailed report on this issue. Chip finds a different selection of peer-reviewed papers that the IPCC ignored. Most interestingly, he has delved into the First Order Draft of the IPCC report and found that in that version, the IPCC said that the rate of increase of Antarctic sea ice was 0.7% +- 0.2% and said this was not significant. When this error was pointed out by reviewers (0.7+- 0.2% is in fact a significant increase), the response of the IPCC was to further massage the data (partly by using annual rather than monthly data) to reduce the trend to 0.5% and to make the trend insignificant.
See also the World Climate Report version of this story. They point out that the TAR indicated a significant increase in antarctic sea ice, making a nonsense of the statement "continues to show interannual
variability and localized changes but no statistically significant
average trends" in AR4. They also find another paper (Watkins and Simmonds, 2000) that found a significant increase in Antarctic sea ice in the 1990s that was ignored by the IPCC.