I I I I

1979 1984 1989 1994 1999 2004

Figure 4.5 Annual averaged sea ice extent in the Southern Hemisphere, 1979-2004, as derived from data from the satellite-borne SMMR and SSMI instruments

Note: The dashed line is the linear least-squares fit through the data points.

Figure 4.6 Annual averaged sea ice extent for 1979-2004, as derived from data from the satellite-borne SMMR and SSMI instruments, for (a) the Bellingshausen and Amundsen Seas and (b) the Ross Sea

Note: The dashed lines are the linear least-squares fits through the respective data points.

The sea ice increase in the Ross Sea is statistically significant at the 99 per cent confidence level, and the sea ice decrease in the Bellingshausen and Amundsen Seas is statistically significant at the 95 per cent confidence level.

The regional sea ice contrasts in the Antarctic correspond well with the known Antarctic atmospheric temperature record. The one region of the Antarctic with a strong record of temperature increases is the Antarctic Peninsula (Hansen et al, 1999; Vaughan et al, 2003), which extends north toward South America and lies immediately to the east of the decreasing sea ice coverage in the Bellingshausen and Amundsen Seas (see Figure 4.6(a)). Furthermore, the greater spatial detail provided by maps of trends in the length of the sea ice season shows that the decreasing sea ice coverage occurs not just to the west of the Antarctic Peninsula, but also to the immediate east, in the far western Weddell Sea (Parkinson, 2002). In fact, the pattern of change in the length of the sea ice season throughout the Southern Ocean has been found to correlate well with the pattern of temperature changes, with warming conditions found in conjunction with shortening sea ice seasons and cooling conditions found in conjunction with lengthening sea ice seasons (Vaughan et al, 2003).

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