Ninth International Conference on Permafrost ... - IARC Research

Climatic Change and Permafrost Stability in the Eastern Canadian CordilleraStuart A. HarrisFaculty Professor, Department of Geography, University of Calgary, Calgary, T2N 1NIntroductionPermafrost is the result of cold climatic conditions, so thestability of the climate is crucial to permafrost stability. Ithas been predicted by modeling that Alaska and the YukonTerritory should exhibit the maximum degree of climaticwarming in the next century (Anisomov & Poliakov2003), but Harris (2007) and Sergeev (2007) found that theavailable climatic data from the most reliable governmentsources indicated no strong warming trends in large partsof these areas. This paper explores the matter further byextending the study south along the Canadian Cordillera andrelating the results to the evidence of associated permafroststability.Sources of DataWhen commencing the study of permafrost distributionin the Eastern Canadian Cordillera in 1974, weather stationsequipped with temperature recorders were used at key sitestogether with ground temperature cables. Observations arecontinuing at the key stations (Fig. 1), which provide a recordof the mean annual air temperature (MAAT), the seasonalthawing index (STI= the sum of the positive mean daily airtemperatures from January 1 to December 31, inclusive) andthe seasonal freezing index (SFI= the sum of the negativemean daily air temperatures from July 1 to June 30). Thedata represent the only available long-term climatic datafrom high altitudes south of the 60 th parallel. The networkwas expanded north into the Yukon Territory, where the datasupplement the data collected by the AES up to 1993 (AES1993) and the climatic data from the Class 1 weather stationsrun by the U.S. National Weather Service. These are the bestavailable data sources for northwest North America.Valley, and in northern British Columbia, there is evidencefor substantial warming. This manifests itself in thawing ofpermafrost north of the crest of the Brooks Range (Osterkamp& Romanovsky 1999) and east of the crest of MacMillanPass along the North Canol road (Kershaw 2003). The SFIhas been decreasing and the MAAT and STI, increasingsince 1980.The main block of the mountains across central andsouthern Alaska and the Yukon Territory, as well as southof 52°25′N in the Eastern Cordillera, shows only minorlong-term changes in MAAT. The SFI has been decreasingsince 1972 in the Watson Lake area, though both the STIand SFI have increased slightly since 1985 at Tuchitua.The permafrost landforms such as palsas and lithalsas shownegligible signs of degradation except where beavers haveraised the local water level resulting in degradation of theadjacent landform, for example, at Wolf Creek (Lewkowicz2003) and at Fox Lake, or where human activity has alteredthe water level (Marsh Lake, north shore, 2007) or throughroad construction, east of Tagish, Y.T. Where the waterlevel is lowered artificially, the ground temperatures in thelandforms cool, and the landforms grow in area (Fig. 3) as atTuchitua. Kershaw (2003) thought that the west side of theMacMillan Pass was also warming due to slow degradationof two floating palsas, but the ponds in which they are foundare becoming shallower and, therefore, warm up more insummer. The peat mounds nearby are not showing increasingground temperatures, and the nearby large palsa fields on thefloodplain of the MacMillan River are not showing evidenceof degradation. It is concluded, therefore, that there is aclimatic divide along the crest of the mountains separatingthe Northwest Territories from the Yukon Territory.ResultsFigure 2 shows the regional pattern of climatic changesince 1980, based on the published climatic data (Harris2007) and the present study. Along the Arctic coast ofAlaska, the east slope of the Cordillera and the MackenzieFigure 1. Location of the study sites.Figure 2. The regional pattern of temperature changes from 1970 to2006 (partly after Harris 2007).93