As detailed in the Drivers report, the key drivers of environmental change are population and economic growth. Antarctica, as the only continent without a native human population, has been subjected to less pressure from human activities than other continents. However, the southern continent, and its surrounding seas and islands have not escaped the effects of these activities. The establishment of permanent stations affects the local environment, and pollution elsewhere on our planet finds its way to Antarctica. For example, human-made chlorofluorocarbon gases have damaged the vital natural sunscreen provided by ozone in the Antarctic stratosphere, human-made CO2 has increased the acidity of the Southern Ocean, and traces of pollutants such as dichlorodiphenyltrichloroethane (DDT) had already found their way into the Antarctic ecosystem by the 1960s (Sladen et al. 1966). Several vertebrate populations were hunted to near extinction in the past, and current economic activities such as fishing and tourism have all had an impact. With an increasing number of stations built on the continent, and more ships and aircraft visiting Antarctica than ever before, pollution with hydrocarbons (e.g. fuel and oil) through leakage and spills is a real risk, particularly for benthic communities (Polmear et al. 2015).
Arguably, the clearest example of large-scale human influence in the Antarctic region is the springtime ozone hole that began forming over Antarctica during the late 1970s (see Box ANT3). The ozone hole has significantly influenced the climate of the Antarctic region, and has caused episodes of unprecedentedly high levels of ultraviolet radiation at Earth’s surface (WMO 2014). As a result of international controls pertaining to ozone-depleting substances, the ozone hole is expected to be largely repaired by the middle of the 21st century, and its effects on solar radiation will dissipate.
Meanwhile, a much more potent and longer-lasting agent of change in the Antarctic region is the continuing anthropogenic emissions of greenhouse gases—in particular, CO2. The Southern Ocean is absorbing vast quantities of CO2. This offsets part of the emissions; however, it is also leading to a change in the ocean’s chemistry, called ocean acidification. For the next 40 years, organisms that occupy high-latitude oceans and that evolved during thousands of years under comparatively stable conditions are expected to be vulnerable to these changed conditions. The physiology and energy requirements of organisms, such as pteropods and molluscs, may be negatively affected (Seibel et al. 2012). Long-term changes in the carbon chemistry of the oceans can reduce the growth rate of the larvae of some fish species, and affect their respiration and behaviour (Frommel et al. 2012). Fish in early life stages lack the ability to self-regulate their internal pH (level of acidity), and tissues can be damaged as the environmental CO2 concentration increases. However, other species may be resilient to these changes in terms of their physiology. Krill populations are already under pressure through increasing ocean temperatures and changes in sea ice cover; the combined effects of these pressures and an increase in ocean acidification could significantly compromise krill recruitment within a century (Kawaguchi et al. 2013).
Increased atmospheric CO2 is also contributing to climate change by warming the lower atmosphere (Myhre et al. 2013). In the Antarctic region, the most significant warming has occurred on the Antarctic Peninsula. From 1951 to 2011, surface temperatures increased by 0.54 °C per decade at Faraday–Vernadsky Station (Turner et al. 2014), whereas the global temperature increase averaged 0.12 °C per decade from 1951 to 2012 (Hartmann et al. 2013). This warming has caused the ice shelves to collapse in the peninsula region (Scambos et al. 2003) and glaciers to retreat in some areas of West Antarctica (Cook et al. 2005). The warming has also decreased the extent of sea ice in the Bellingshausen Sea (Thomson & Solomon 2002).
The average near-surface temperatures across the entire continent have been estimated to have increased by 0.11 ± 0.08 °C per decade from 1958 to 2012 (Nicolas & Bromwich 2014). Greater overall warming is observed in West Antarctica than in East Antarctica. Although the continent is showing an overall warming, some regions have exhibited cooling trends, particularly in autumn (Nicolas & Bromwich 2014, Turner et al. 2016). Increasing air and ocean temperatures cause changes in snowfall patterns (Bromwich et al. 2011), which in turn affect the quality, extent and durability of sea ice. For example, near Davis research station, a long-term monitoring study of sea ice detected a delay in the time when the maximum thickness is reached by the nearshore or ‘fast’ ice, and attributed this trend to the warmer winters in recent years (Heil 2006).
Assessing the overall impact that climate change will have on the physical systems of Antarctica is difficult. A lack of data exists for large parts of the continent, and timeseries tend to be too short or are available for only a small number of locations. The processes driving weather patterns and underlying climate change are complex, because they can operate on different temporal and spatial scales, and either increase or counteract each other. Some connections—for example, between atmospheric and oceanic phenomena—are still poorly understood.
Similarly, although we know that it is highly likely that climate change will alter ecosystems, the processes involved are complex and not fully understood (Constable et al. 2014, Larsen et al. 2014). Some biological models have explored the consequences of climate change for individual species, but ecosystem models are still in development (Murphy et al. 2012). Predicting how organisms will respond individually or collectively to climate change and other human-induced pressures is a major challenge for current research. We do not know which species may be able to adapt to the changing environment through genetic responses. Some organisms may even benefit from the effects of climate change, at least in the short term. For example, more ice-free areas offer potential habitat for plants and animals. However, the long-term consequences are hard to predict and will depend on the degree to which the atmosphere warms.
The restoration of ozone levels during the next several decades will also have a significant effect on the region. This will generally return ultraviolet exposure to near or even below pre–ozone hole levels (WMO 2014), to the advantage of many species, particularly in the Antarctic Peninsula region. However, during the repair phase, weakening of the temperature gradients produced in the Antarctic stratosphere by the ozone hole will allow the effects of greenhouse gas increases to more strongly influence the Antarctic climate—further increasing Antarctic temperatures—particularly in East Antarctica during summer.