Earth’s polar regions are likely to be affected by changing climate conditions. These changes represent the highest risk to the region, since they are unlikely to be mitigated by any locally implemented management measures. The impacts of climate change on the Antarctic environment are detailed in the Introduction section of this report.

Population and economic growth are leading to other risks. Many fish stocks around the world are depleted or fully exploited and few are given the chance to recover. A growing human population has led to demands for new sources of protein, and thus the pressure on the industry to catch krill is likely to increase. In the past, the fishing nations that are active in the Southern Ocean had never reached the catch limits for krill set by CCAMLR. However, in the 2009–10 season, the fishery reached the trigger level in one of the subareas in the South Atlantic, and, for the first time, the fishery was closed before the end of the fishing season. Since then, consecutively in the 2012–13, 2013–14 and 2014–15 seasons, the trigger limit was reached in the same subarea, and earlier each year (June, May and May, respectively). Newly developed technology has allowed vessels to catch a maximum of about 800 tonnes per day, compared with about 400 tonnes landed by conventional vessels (Nicol et al. 2011). This advanced fishing technology has contributed to a rise in the krill catch to almost 300,000 tonnes in 2014, and high catch rates may force the krill fleet to expand into new areas to avoid exceeding the existing catch limits.

The consequences of krill fishing continuously operating at the catch levels set by CCAMLR are unknown, but have been evaluated to be sustainable and consistent with the maintenance of krill-dependent predators. The impact on the krill population of environmental changes, such as ocean acidification (Kawaguchi et al. 2009), will also have to be considered when recalculating precautionary catch limits for Southern Ocean fisheries.

Recently, the IUCN Red List categorised Antarctic krill as ‘least concern’. The assessment is based on krill biology—including its generation time, mortality and population size—and current management action. The ‘least concern’ categorisation was given primarily because there are no trends detected in the most recent 3-generation time period (15 years) and because of the very large population size. The cumulative impacts of climate change, including ocean acidification, were identified as the major threat. Regarding conservation actions recommended by the IUCN, conservation needs to include continued precautionary management of the fishery and more research on the impact of climate change on this species.

Acidification of the world’s oceans is occurring because of several concurrent processes, but there is still much uncertainty about how, for example, climate change affects these processes. It is well established that levels of anthropogenic CO₂ are increasing in the atmosphere, transferring 1 million tonnes of CO₂ to the world’s ocean per hour (Hester et al. 2008). For the Southern Ocean, the process of overturning circulation (where deep water upwells and releases CO₂ to the atmosphere) is particularly important. As the atmosphere warms, surface waters warm, which increases stratification and limits gas exchange of this upwelled water with the atmosphere. This, in turn, causes greater retention of CO₂, allowing more time for respiration of organic matter by marine bacteria. All these processes increase acidification (Hester et al. 2008). Several studies are highlighting diverse and sometimes unexpected consequences on marine ecosystems:

• The effects of ocean acidification on the availability of nutrients compromise the ability of organisms to deposit and maintain exoskeletons of calcium carbonate. With less calcium in their shells, they are lighter and less likely to sink into deeper waters. This reduces the flux of organic material to the deep ocean (a process known as the ‘biological pump’, which sequesters carbon from the atmosphere to the deep sea) and increases the amount of CO₂ in the upper water column (Hofman & Schellnhuber 2009). The overall effect of climate change on the biological pump is influenced by many competing pathways (e.g. photosynthesis, grazing, sinking, respiration). The outcome is currently uncertain, but is likely to have severe biological impacts within decades, and could dramatically affect the structure and function of marine ecosystems (Feely et al. 2004; Orr et al. 2005, 2009; Doney et al. 2009b; Hutchins et al. 2009; Shi et al. 2010). Such changes would have profound effects on ecosystem services, including the productivity of fisheries and the efficiency of the Southern Ocean sink for atmospheric CO₂. These changes are most pronounced in the polar regions, where the acidity of the waters is changing twice as fast as in the warmer tropical and subtropical regions.
• Growth and survival of fish populations could be impaired in an acidifying ocean. Tropical fish larvae that were exposed to increased levels of CO₂ changed their behaviour in a way that made them 5 to 9 times more prone to predation. Such an increase in mortality can reduce the long-term survival of fish populations (Munday et al. 2010).
• A decrease in the ocean’s pH may affect the absorption of sound in the ocean, making the oceans noisier (Hester et al. 2008, Ilyina et al. 2009). Whether this will affect marine mammals —for example, in their ability to communicate—is currently unclear.

Human activities are increasing on the Antarctic continent. The human footprint on Antarctica is small compared with the total size of the continent; however, the impacts are not evenly spread. Human activity and associated impacts are concentrated around stations, which tend to be built on ice-free land close to the sea. This land is also important habitat for the plants and animals of Antarctica. In East Antarctica, many ice-free areas have stations, and new stations are now being commissioned. Currently, more than 50 research stations across Antarctica accommodate up to 4000 people during summer and 1000 during winter (Tin et al. 2009).

Mining and mineral exploration activities are banned indefinitely in the Antarctic Treaty area through the Madrid Protocol. The Madrid Protocol and CCAMLR have so far been successful in managing human activities in the Antarctic region, and achieving their environmental protection and conservation objectives.