To assess the future of Antarctica and the Southern Ocean, a global perspective is required. Despite Antarctica’s remoteness from centres of human population, the pressures generated in the rest of the world affect Antarctic and Southern Ocean ecosystems through the linkages provided by atmospheric and oceanic circulations. Although the rate has slightly decelerated, the global human population is still increasing and is expected to reach 9.3 billion in 2050 (UN 2015). Increasing demands for protein sources can only increase the possibility that, at some stage, people will look to Antarctica and the Southern Ocean to source them, especially when existing sources reach their limits in other parts of the world.

Recent assessments of the impacts of climate change on Antarctica and the Southern Ocean highlight that changes have been observed in the Antarctic environment, and continued changes are expected in the climate and weather patterns of Antarctica, as well as in the physical and chemical properties of the Southern Ocean (SCAR 2009, Turner et al. 2014). Although many of the underlying processes driving the changes are still not well understood, the processes that are changing the Antarctic environment appear to be well under way and likely to continue for at least the next several decades.

Although several indicators vary markedly in their regional expression and intensity (particularly between West and East Antarctica), overall trends in the Antarctic system are similar throughout the region. The Fifth Assessment Report of the Intergovernmental Panel on Climate Change predicts that future Antarctic changes will include (Stocker et al. 2013):

• warming of the Southern Ocean and freshening of at least its upper water masses
• warming of the Antarctic surface
• strengthening of the Southern Annular Mode (SAM).

The strengthening of the SAM is currently countering part of the warming of the surface that is accompanying increasing greenhouse gas levels, particularly during summer. During the next half-century, it is likely that the rate of warming of the Antarctic surface will increase as the forcing of the SAM by ozone depletion diminishes (WMO 2014).

During the next decades, particularly if the production of anthropogenic CO₂ continues at its present rate, ocean acidification will become more pronounced in the cold Southern Ocean than in warmer regions. The amount of CO₂ that can be absorbed by the Southern Ocean is limited, and, if CO₂ production is not reduced, the Southern Ocean may no longer act as a CO₂ sink. A similar effect will be achieved as the ocean warms, because warmer waters have less capacity to act as a CO₂ sink than cold waters. For the past 2 centuries, the hydrogen ion concentration of surface water has increased by approximately 25 per cent in the world’s oceans, lowering the pH by 0.1 unit and making the water less alkaline. The current rate of change is about 100 times higher than that shown by the palaeorecord (Royal Society 2005). Given the amount of CO₂ already in the atmosphere, a reversal of ocean acidification is unlikely in our lifetime (Royal Society 2005).

In all likelihood, the distribution of species will change as those adapted to warmer climes expand their ranges south. Those organisms already existing in the high Antarctic either must adapt or will disappear. The most likely candidates to vanish in the long term are those that have adapted to live within very narrow environmental limits. This limitation, plus their generally long lives, mean that, with the increasing rate of change in their environment, fewer and fewer generations will be able to acclimatise and adapt to the new conditions. Range expansions have already been reported from the Antarctic Peninsula region. Some animal, plant and microorganism populations are expected to expand in areas where more liquid water will become available and temperatures will increase.

We cannot yet predict the extent to which biodiversity will be affected by the expected future changes. However, ocean acidification, in particular, is likely to have a profound effect on the Antarctic ecosystem because it affects organisms at the base of the food web. Whatever changes may occur in the biodiversity of Antarctica, the effects are expected to cascade through the entire ecosystem.