Permafrost: changes and impacts

Abstract

Industrial activities and those of stakeholders in northern regions occur in close relationship with permafrost and periglacial processes. The significant role of permafrost relates to the dependence of its mechanical and physical properties on the temperature (especially if the temperature is close to 0 °C). These properties change dramatically if permafrost becomes unstable and starts to melt. All kinds of engineering constructions in Arctic regions are effected by cold climate and permafrost. The permafrost conditions determine the principles of design, construction and use of the engineering works. Permafrost also has direct impacts on the subsistence activities of local residents and their food sources.

Permafrost within Alaska varies from cold continues permafrost (-6 to -10 °C) on the North Slope to discontinuous and sporadic permafrost in Fairbanks area and further south to Glennallen and Anchorage with temperatures at the permafrost surface of 0 to -2 °C. Recent studies show that active layer thicknesses and permafrost temperatures here exhibit significant interannual and decadal time scale variations, which can create engineering problems even within the continuous permafrost zone. Moreover, permafrost in many regions of the earth is currently warming. Lachenbruch and Marshall [20] used temperature measurements in permafrost to show there has been a general warming of the permafrost in the Alaskan Arctic of 2 to 4 K over the last century.

Our temperature measurements made over the last two decades show that permafrost has warmed at all sites along a north-south transect that spans the continuous and most of the discontinuous permafrost zones of Alaska from Prudhoe Bay to Glennallen. Modeling indicates that in the continuos permafrost zone, mean annual permafrost surface temperatures vary interannually within the range of more than 5 K. In the discontinuous permafrost, the observed warming is part of a warming trend that began in the late 1960s. Total magnitude of the warming at the permafrost surface since then is about 2 K. The last “wave” of the recent warming according to observed data began on the Arctic Coastal Plain, in the Foothills and at Gulkana in the mid-1980s (typically 1986 or 1987) and in areas of discontinuous permafrost about 1990 (typically 1989 to 1991). The magnitude of the observed warming at the permafrost surface is about 3 to 4 K at West Dock and Deadhorse, Prudhoe Bay region, about 2 K over the rest of the Arctic Coastal Plain and south into the Brooks Range and typically 0.5 to 1.5 K in discontinuous permafrost. At some sites in discontinuous permafrost south of the Yukon River, permafrost is now thawing from both the top and bottom. Thawing of ice-rich permafrost is presently creating thermokarst terrain which has significant effect on Sub-Arctic ecosystems and infrastructure. Consequently, for any future warming, the greatest impacts of thawing permafrost will occur in areas of warm ice-rich discontinuous permafrost.