The physical and chemical components of the Antarctic environment are changing. The Antarctic surface and lower atmosphere are warming, with the strongest temperature increases in the Antarctic Peninsula region and West Antarctica. Part of the warming is because of global temperature increases that are accompanying the rise in atmospheric greenhouse gas concentrations. Antarctic temperature changes are also being influenced by shifts in atmospheric circulation as a result of stratosphere cooling through ozone depletion and increasing levels of carbon dioxide, and variability in the heat content of the oceans. Most notably, there is strong evidence that stratospheric ozone depletion associated with the Antarctic ozone hole has mitigated the warming of much of Antarctica during the summers of the past 2–3 decades. There is increasing evidence that the ozone layer is starting to recover as a direct consequence of international controls on the use of human-made ozone-depleting substances.

The complex Antarctic food web is based on vast numbers of marine microorganisms, including bacteria, phytoplankton and zooplankton. Changes to the marine environment, including ocean acidification, will have a significant impact on these organisms. Since these organisms are at the base of the food web, such changes will have profound effects throughout the Antarctic ecosystems.

Few data are available about the status of Antarctic vertebrates, which encompass a variety of flying seabirds and penguins, several seals and whales, and numerous fish. The distribution and abundance of humpback whales are probably the best known of any whale species. Recent surveys indicate that some stocks are increasing to a point that their delisting as a threatened species under Australian legislation has been proposed. There is some evidence that the breeding distribution of Adélie penguins has expanded during the past decade; however, the size of emperor penguin colonies may have declined. Similarly, although several fur seal populations appear to be increasing, the numbers of southern elephant seals at Macquarie Island are declining. Climate change and warming conditions are also supporting the movement of non-native species into the region, where they may outcompete native species. Introduced plants, such as annual meadow grass (Poa annua), are thriving on Australia’s subantarctic islands.

Many subantarctic islands also carry the legacy of introduced vertebrates, such as rabbits or pigs that were released during the sealing years onto the islands as food sources. A notable step has been taken in the past few years to redress the damage cause by introduced species in the subantarctic through the successful eradication of rabbits, rats and mice on Macquarie Island.