Since 2011, the Antarctic environment has continued to respond to global pressures from human activity. As is the case in other regions of the globe, long-term trends in characteristics of the Antarctic physical environment are emerging against a backdrop of intrinsic variability that operates on various spatial and temporal scales. At any particular location, the intrinsic variability is dictated over hours to several days by meteorological processes, while various modes of the climate system—most notably the Southern Annular Mode, the El Niño–Southern Oscillation and the Pacific Decadal Oscillation—influence the Antarctic region across seasonal to decadal timescales. In general, in situ measurements of the physical environment in the Antarctic region continue to be relatively restricted in spatial and temporal extent compared with elsewhere.
Antarctica is generally warming, continuing the trend apparent during the latter half of the 20th century, although regional and temporal variations in long-term climate behaviour are apparent (Turner et al. 2014). Although some areas of the Antarctic Peninsula and West Antarctica rapidly warmed in the late 20th century, recent temperature trends on the Antarctic Peninsula are less marked and show greater consistency with the natural variability of the climate system (Turner et al. 2016). Coastal East Antarctica is generally warming, although the trend is weaker than in West Antarctica, and in some regions and seasons shows evidence of cooling (Turner et al. 2014).
Further indications of improvement in stratospheric ozone levels above Antarctica in spring and summer are emerging, although meteorological factors continue to significantly influence the year-to-year severity of the ozone hole (Solomon et al. 2016). For example, estimated effective levels of ozone depleting substances in the Antarctic stratosphere decreased from approximately 93 per cent to 89 per cent of their peak value in 2000 in the past 5 years (an improvement of 4 per cent). Although continued ozone improvement is expected because of the Montreal Protocol on Substances that Deplete the Ozone Layer, the Antarctic ozone hole will continue to have an important influence on Southern Hemisphere summer climate in the coming 2–3 decades, primarily by helping to maintain the changes in the westerly winds that developed over the Southern Ocean towards the end of the 20th century (Eyring et al. 2013).
The Southern Ocean is changing in ways that are likely to affect regional and global climate, and marine productivity (Rhein et al. 2013). Ocean temperatures around the Antarctic continent have increased more rapidly and to greater depth than the global average in recent decades (Roemmich et al. 2015). This warming has been linked to glacier retreat and ice-shelf disintegration in West Antarctica (Miles et al. 2013), and indications of increased basal melt of the Antarctic ice sheet (Schodlok et al. 2016). The extent of sea ice around Antarctica has shown a small overall annual increase in recent decades, particularly in the Ross and Weddell seas, which is linked to climate variability in the Pacific Ocean (Meehl et al. 2016). There have been, however, significant regional decreases in the Amundsen and the Bellingshausen seas (Hobbs et al. 2016a).
Changes to the marine environment, including ocean acidification, are having a significant impact on keystone organisms such as krill. Krill embryos are likely to be negatively affected by increasing ocean acidification, which may significantly reduce hatching success (Kawaguchi et al. 2013). Since krill is near the base of the food web, these changes may have profound effects throughout Antarctic ecosystems, particularly on dependent predators such as seabirds, seals and whales.
Overall, the quality of the East Antarctic environment has not significantly changed since 2011, and Australia has continued to demonstrate a strong commitment to Antarctic research and policy development for global benefit. However, various pressures from global climate change continue to influence Antarctica. Arguably, the most significant ongoing risks to society from these changes are posed by Antarctica’s increasing contribution to sea level rise from ice-sheet melting, and the potential for reduced productivity and diversity of the Southern Ocean ecosystem because of increasing ocean acidification.