The Antarctic record

In terms of demonstrating a long-term pattern reflective of global warming, the Antarctic sea ice record is not nearly as convincing as the Arctic record. This was not the case in 1981, when Kukla and Gavin (1981) published a paper showing a striking decrease in Antarctic sea ice coverage that occurred in the 1970s. At the time, this Antarctic sea ice decrease was heralded as perhaps the first really strong geophysical evidence of global warming. The ice decrease of the 1970s, however, has not continued.

As with the Arctic record, the satellite record of Antarctic sea ice shows considerable interannual (see Figure 4.5) and regional (see Figure 4.6) variability. The overall trend since 1979, however, shows increasing rather than decreasing sea ice coverage (see Figure 4.5). The trend magnitude is not nearly as large as for the Arctic sea ice decrease, but, at 14,000 ± 5200 km2/yr (1.24 ± 0.46 per cent per decade), it is still substantial and is statistically significant at the 99 per cent confidence level. The increasing Antarctic sea ice coverage since the late 1970s has been reported by Stammerjohn and Smith (1997), Watkins and Simmonds (2000), and Zwally et al (2002), for the periods 1979-1994, November 1978-December 1996, and November 1978-December 1998, respectively.

Regional studies of Antarctic sea ice frequently divide the Southern Ocean into five regions. Of these, the Ross Sea, immediately north of the Ross Ice Shelf, shows the strongest trend towards increasing sea ice coverage over the 1979-2004 period (Figure 4.6(b)), while the region of the Bellingshausen and Amundsen Seas, between the Ross Sea on the west and the Antarctic Peninsula on the east, is the only region with a decreasing 1979-2004 sea ice cover (see Figure 4.6(a)).

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