IPCC Fourth Assessment Report: Climate Change 2007
Climate Change 2007: Working Group II: Impacts, Adaptation and Vulnerability

15.6.3 Case study: Antarctic Peninsula – rapid warming in a pristine environment

The Antarctic Peninsula is a rugged mountain chain generally more than 2,000 m high, differing from most of Antarctica by having a summer melting season. Summer melt produces many isolated snow-free areas, which are habitats for simple biological communities of primitive plants, microbes and invertebrates, and breeding grounds for marine mammals and birds. The Antarctic Peninsula has experienced dramatic warming at rates several times the global mean (Vaughan et al., 2003; Trenberth et al., 2007). Since the TAR, substantial progress has been made in understanding the causes and profound impacts of this warming.

Since records began, 50 years ago, mean annual temperatures on the Antarctic Peninsula have risen rapidly; >2.5°C at Vernadsky (formerly Faraday) Station (Turner et al., 2005). On the west coast, warming has been much slower in summer and spring than in winter or autumn, but has been sufficient to raise the number of positive-degree-days by 74% (Vaughan et al., 2003), and the resulting increase in melt has caused dramatic impacts on the Antarctic Peninsula environment, and its ecology.

Around 14,000 km2 of ice have been lost from ten floating ice shelves (King, 2003), 87% of glacier termini have retreated (Cook et al., 2005), and seasonal snow cover has decreased (Fox and Cooper, 1998). The loss of seasonal snow and floating ice do not have a direct impact on global sea level, but acceleration of inland glaciers due to the loss of ice shelves (De Angelis and Skvarca, 2003; Scambos et al., 2004; Rignot et al., 2005) and increased run-off of melt water (Vaughan, 2006) will cause an increase in this contribution. If summer warming continues, these effects will grow.

Marine sediment cores show that ice shelves probably have not reached a similar minimum for at least 10,000 years (Domack et al., 2005), and certainly not for 1,000 years (Pudsey and Evans, 2001; Domack et al., 2003). This suggests that the retreat is not simply due to cyclic variations in local climate, and that recent warming is unique in the past 10,000 years (Turner et al., 2007). The processes leading to warming are unclear, but appear to be correlated with atmospheric circulation (van den Broeke and van Lipzig, 2003) and particularly with changes in the Southern Annular Mode caused by anthropogenic influence (Marshall et al., 2004; Marshall et al., 2006). The winter warming on the west coast also appears to be related to persistent retreat of sea ice (see Figure 15.2; Parkinson, 2002) and warming in the Bellingshausen Sea (Meredith and King, 2005). The spring depletion of ozone over Antarctica (the Antarctic Ozone Hole) has also been implicated in driving circulation change (Thompson and Solomon, 2002), but this has been disputed (Marshall et al., 2004). Current general circulation models (GCMs) do not, however, simulate this observed warming over the past 50 years (King, 2003) and we cannot predict with confidence whether rapid warming will continue in future.

If warming does continue (especially in the summer) there will be significant impacts; retreat of coastal ice and loss of snow cover would result in newly exposed rock and permafrost – providing new habitats for colonisation by expanding and invading flora and fauna. However, the direct impacts of climate change on the flora and fauna are difficult to predict, since these ecosystems are subject to multiple stressors. For example, increased damage by ultraviolet exposure, because of reduced ozone levels and summer desiccation, may oppose the direct responses to warming (Convey et al., 2002). In addition, there is a growing threat of alien species invasion, as climatic barriers to their establishment are eroded by climate amelioration, and increasing human activity increases the opportunity for introduction. Such invasions have already occurred on many sub-Antarctic islands, with detrimental consequences for native species (Frenot et al., 2005). Furthermore, slow reproduction rates during rapid climate change may limit the possible relocation of native species.

There have been trends in all trophic levels in the marine ecosystems west of the Antarctic Peninsula. These have been driven by reduced sea-ice extent and duration. Changes in primary production may also have been affected by increases in the supply of glacial melt (Smith et al., 2003). Similarly, reduced sea-ice cover was the likely cause of the dramatic change in the balance between krill and salps, the main grazers of phytoplankton (Atkinson et al., 2004). The loss of krill will probably have impacts on higher predators (albatrosses, seals, whales and penguins: populations of the latter are already changing; Smith et al., 2003), but could have more far-reaching impacts, perhaps even affecting CO2 sequestration in parts of the Southern Ocean (Walsh et al., 2001).

The global significance of the Antarctic Peninsula warming is difficult to encapsulate, but the main concern is for the loss of a unique landscape and biota. The rate of warming on the Antarctic Peninsula is among the highest seen anywhere on Earth in recent times, and is a dramatic reminder of how subtle climate-dynamic processes can drive regional climate change, and the complexity of its impacts in an environment where human influence is at a minimum.