The key process threatening the resilience of both the physical and living environments of Antarctica is climate change.

The Antarctic and Southern Ocean physical environments are key components of the overall global climate system. The Southern Ocean plays a major role in buffering heat and CO₂ uptake, thereby slowing the rate of climate change and impacts, and providing some resilience on a planetary scale. However, this comes with the problem of ocean acidification, which is nonresilient in that CO₂ levels remain elevated long after the cessation of emissions (Archer & Brovkin 2008).

Changes in the physical environment may be gradual or abrupt, and are complicated by feedbacks. The primary issue is the potential for state changes as climate change thresholds are crossed. As discussed in earlier sections of this report, large changes are already seen (e.g. ice loss from parts of West Antarctica, changes in the deep ocean), and conditions are thought to exist that could see more extensive or rapid changes in future.

Large uncertainties exist around the response and resilience of the physical system. Reducing these uncertainties requires several lines of research:

• studying past behaviour using palaeoclimate data
• observing present behaviour with long-term monitoring
• modelling to explore current change and predict the future.

For the living environment, the question of the level of resilience inherent in Antarctic ecosystems has not received much attention because it is complex and many parameters that are required to assess resilience are still unknown. The Scientific Committee on Antarctic Research produced a comprehensive review of the impact of climate change on the Antarctic environment in 2009, which highlighted areas where knowledge is still lacking. Although marine and terrestrial ecosystems are now better understood than in the past, baseline data on biogeography and biodiversity are still scarce, as are fundamentally important long-term monitoring data (SCAR 2009). Researchers have only just started to investigate how organisms adapt to current climate change, and how resistant and resilient organisms and systems are.

For many, if not most, vertebrate species, important aspects of the dynamics of populations are either largely unknown or have been studied only at a few sites. Without comprehensive insights into variables—such as age of first reproduction, survival of different age classes, fecundity, and the extent of emigration out of and immigration into populations—and the drivers that influence these variables, we are unable to make long-term predictions about the viability of species in a changing environment. A thorough understanding of the ecological framework in which organisms live is also important when considering their resilience. For example, several Antarctic organisms live at South Georgia, where the summers are up to 3 °C warmer than on the Antarctic Peninsula. Thus, the vulnerability of species needs to be determined based on their ecological circumstances (SCAR 2009).

Natural disturbances are part of life in Antarctic and subantarctic ecosystems, and the populations of endemic species are generally capable of surviving shock events because they have evolved strategies that allow them to rebuild after mass mortalities. Among these strategies are longevity among seabirds, and the ability of moss spores to survive for a long time.

Shock events that test the level of resilience of a system occur in Antarctica just as they do in other parts of the world, ranging from intense storms affecting large areas to more localised incidents, such as scouring of the benthic environment by drifting icebergs. As long as these shock events are rare, populations and communities can recover. However, increases in the magnitude and frequency of such events, as well as the duration of serious disturbances, are likely to become major challenges to the resilience of benthic communities. The slowest-growing species may never recover if the interval between disturbance events is too short for them to develop and grow into mature organisms. However, populations of fast-growing species may benefit if the competition for space, for example, is reduced.

Historically, we know that populations of some species of whales, seals and penguins suffered human-induced mortality rates that pushed these species to the brink of extinction. Once hunting ceased, several species recovered—some, like king penguins, in a spectacular manner (Gales & Pemberton 1988, van den Hoff 2009).

However, these recoveries took place in a world where environmental conditions were not exposed to the rapid change that is currently under way. Today, several environmental components are changing (e.g. increasing sea temperatures, ocean acidification, higher intensities of ultraviolet radiation). The changes are complex and not always unidirectional, and there is currently little evidence on how the various factors will interact. There is no doubt that some organisms will benefit from these changes in the short term, but it is difficult to predict the effect of rapid climate variations on ecosystems. Many species may be vulnerable because their capacity to adapt operates at a much slower rate than the changes currently observed.