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Third Assessment report: Climate Change 2001. Working Group II Report “Impacts, Adaptation & Vulnerability

Introduction: For the purposes of this assessment, the Arctic is defined as the area within the Arctic Circle. It covers the Arctic Ocean and the islands and northern continental land areas (see Figure 16-1). Thus, it extends far enough south to include parts of the boreal forest and discontinuous permafrost zone. Note that the Arctic, thus defined, overlaps with other regions covered in this report—namely, North America, Asia, and Europe—and that important physical and biological processes that are typical of the Arctic also occur south of the Arctic Circle. The Antarctic is defined here as the Antarctic continent, together with the surrounding Southern Ocean south of the Antarctic Convergence (polar front), an oceanographic barrier that shifts with time and longitude but generally is close to 58°S. Also included in the polar regions are sub-Antarctic islands such as Campbell Island, Heard Island, and South Georgia, some of which are north of the Antarctic Convergence (see Figure 16-2).

The two polar regions are dominated by cold conditions and the presence of ice, snow, and water. They are different in that the Arctic is a frozen ocean surrounded by continental landmasses and open oceans, whereas Antarctica is a frozen continent surrounded solely by oceans. Antarctica tends to be thermally isolated from the rest of the planet by the surrounding Southern Ocean and the atmospheric polar vortex, whereas the Arctic is influenced strongly by seasonal atmospheric transport and river flows from surrounding continents. Both regions have major influences on the global ocean.

The Arctic and Antarctic influence climate over a significant part of the globe. Many unique climatic processes operate in these regions. Some involve complex interactions and feedback loops (Simmonds, 1998) that may lead ultimately to glacial-interglacial climate transitions (Petit et al., 1999). Processes in polar regions greatly influence sea level. The Arctic and Antarctic have food webs and natural ecosystems with remarkable productivity. The Arctic is on the periphery of human settlement, where people must adapt to harsh, cold regimes; the Antarctic is uninhabited apart from research bases.