Satellite data collected since 1978 confirms that over the last three decades there has been significant decline in the extent of arctic sea ice. Winter ice cover has shrunk at a rate of 2.8% per decade, with the extent of summer sea ice shrinking at a rate of 11.1% per decade (Richter-Menge et al 2008).

The amount of summer sea ice in the northern hemisphere dropped to a record low in 2007. Summer sea ice levels recovered slightly in 2008 but the level was still well below the 1979-1983 average. The strong long-term trend over the past three decades is a decline in arctic sea ice (see Figure 3). In fact, the recent summer minimums of sea ice have happened about 30 years ahead of current climate model projections (Climate Adaptation Science and Policy Initiative 2007).

Figure 3: Daily ice extents 2005, 2007, and 2008, and averaged over the 5-yr periods 1980-84 through 2000-04. Values are derived from satellite passive microwave data from NASA's SMMR and the Department of Defence's SSM/I. (Adapted from Cosimo et al. 2008, in Richter- Menge at al 2008 see http://www.arctic.noaa.gov/reportcard/seaice.html 3.

The story in Antarctica is more complex. It is true that satellite images taken over the last thirty years show an upward trend in the extent of sea ice in Antarctica. However, by studying ice cores the Australian Antarctic Division was able to estimate ice cover as far back at the 1840s. This research concluded that there has in fact been a 20% decline in sea ice cover since the 1950s (Australian Antarctic Division 2004).

Recent observations show large sections of ice breaking apart in areas of Antarctica. This includes approximately 1,350 km2 of the Wilkins Ice Shelf breaking apart over the period May-July 2008 (European Space Agency 2008). While it is too early to make firm conclusions, these events do raise the prospect of that the long-term decline in Antarctica’s sea ice may be restarting after several decades of growth. This would be consistent with rapid warming observed in Antarctica, where temperatures have risen by more than 3oC over the past 50 years, which is up to six times the global average (Australian Antarctic Division 2008).

J. Richter-Menge, J. Comiso, W. Meier, S. Nghiem, and D. Perovich (2008), “Sea Ice Cover” in: J. Richter-Menge et al (2008), Arctic Report Card 2008: Tracking recent environmental changes, National Oceanic and Atmospheric Administration (NOAA), http://www.arctic.noaa.gov/reportcard/ArcticReportCard_full_report.pdf.

Climate Adaptation Science and Policy Initiative (2007), Evidence of Accelerated Climate Change, The Climate Institute, Sydney, www.climateinstitute.org.au.

Australian Antarctic Division (2004), “Ice core evidence for 20% decline in Antarctic sea ice extent since the 1950s”, Australian Antarctic Magazine, Issue 6, http://www.aad.gov.au/default.asp?casid=14700.

European Space Agency (2008), “Wilkins Ice Shelf under threat”, online material: http://www.esa.int/esaCP/SEMXK5AWYNF_Protecting_0.html

Australian Antarctic Division (2008), “Rapid disintegration of another ice shelf on the Antarctic Peninsula”, Australian Antarctic Magazine, Issue 14, http://www.aad.gov.au/default.asp?casid=34677.