The Australian Antarctic Territory: Climate, atmosphere and the ice

Independent report to the Australian Government Minister for the Environment and Heritage
Beeton RJS (Bob), Buckley Kristal I, Jones Gary J, Morgan Denise, Reichelt Russell E, Trewin Dennis
(2006 Australian State of the Environment Committee), 2006

10.1 Climate, atmosphere and the ice

Two salient features of Antarctica are its remoteness from human settlements and the dominance of ice. These characteristics give Antarctica, as well as many other isolated areas, a valuable role in monitoring global climate change.

Ultraviolet radiation values at Australian stations are elevated, relative to expectations for sites at comparable northerly latitudes, and this is directly attributable to stratospheric ozone depletion  (the 'ozone hole'). However, ozone loss over Antarctica appears to have stabilised during the 1990s (see ‘Atmosphere’).

In the Territory, temperatures  have neither increased nor decreased, which is consistent with records from across most of Antarctica. The area of sea ice  has varied from year to year (Parkinson 2004), with the only significant increase since the 1970s being in the Ross Sea area. The total volume of continental ice has actually increased, but not consistently. The ice volume in east Antarctica has increased while large parts of west Antarctica have experienced decreases. In contrast, the Antarctic Peninsula (which is not part of the Australian Antarctic Territory) appears to have become warmer, and accordingly has a smaller area of sea ice and a lower volume of ice overall (Zwally et al 2002).

A recent study of proxies for sea ice extent derived from analysis of coastal ice cores indicate, however, that there may have been consistent decline in sea ice extent around East Antarctica in the last 50 years despite large annual variations (Curran et al. 2003, Figure 37). Similar changes in sea ice extent have been inferred also from analyses of historical whaling records (de la Mare 1997) and penguin populations (Wilson et al 2001, Barbraud and Weimerskirch 2001).

Figure 37: Change in the extent of sea ice, 1850–2000

 Change in the extent of sea ice, 1850-2000

Note: Methanesulphonic Acid (MSA) records from an ice core from Law Dome in East Antarctica and inferred northern most latitude extent of winter sea ice (SIE) off East Antarctica between 80°E and 140°E.  The MSA record covers the period 1841 to 1995.  The light blue line is the 3-year running mean MSA measurement and the purple line is the 20-year running average.  The red line is the maximum winter sea ice extent measured by passive microwave between 1973 and 1994 (J. Jacka  unpublished data).   
Source: Curran et al (2003)

Sub-Antarctic glaciers  tell a more consistent story. Heard Island’s glaciers have retreated in extent since 1947, and the total land area covered by glaciers has decreased from 288 square kilometres in 1947 to 253 square kilometres in 2000 (Ruddell 2006). Thirty-five square kilometres of new terrain, including several large lagoons, have been exposed by ice retreat. This represents nearly 10 per cent of the total area of the island. Areas of vegetation  are increasing as a consequence.

Some signals are starting to emerge from the study of Australia’s Antarctic Territory. Recent surveys of the Southern Ocean off East Antarctica have revealed that the deep ocean water  is markedly fresher and less dense than expected and has become progressively so over the last 30 years. The exact causes of these changes are not yet resolved, but the results indicate that the Southern Ocean is changing much more rapidly than previously considered likely (Rintoul in press).

These changes are significant. Variations in the winter extent of sea ice have a key role in global oceanic circulation. They are thought to have effects on the productivity of algal growth under the ice and the reproduction of Antarctic Krill (Euphausia superba), a small, highly abundant crustacean which is a major component of the Antarctic food chain.