Permafrost, defined as sub-surface earth materials that remain at or below 0°C continuously for two or more years, is widespread in Arctic, sub-Arctic and high-mountain regions, and in the small areas of Antarctica without permanent ice cover. The physical processes of climate-permafrost interactions and observations of permafrost change are discussed elsewhere (Lemke et al., 2007); here we focus on the observed and projected changes of permafrost, and impacts they may have on natural and human systems in the Arctic.
Observational data are limited, but precise measurements in boreholes indicate that permafrost temperatures in the Arctic rose markedly during the last 50 years (Romanovsky et al., 2002), with rapid warming in Alaska (Hinzman et al., 2005), Canada (Beilman et al., 2001), Europe (Harris et al., 2003) and Siberia (Pavlov and Moskalenko, 2002). Short-term and localised warming associated with the reduction of snow cover (Stieglitz et al., 2003) and feedbacks associated with increased vegetation productivity (Sturm et al., 2001; Anisimov and Belolutskaia, 2004; Chapin et al., 2005b) are, however, important considerations that must be taken into account.
In the context of the future climate change, there are two key concerns associated with the thawing of permafrost: the detrimental impact on the infrastructure built upon it, and the feedback to the global climate system through potential emission of greenhouse gases. These are discussed in Sections 15.7.1 and 220.127.116.11.