| Summary: | Many new ground temperature measurement boreholes have been established, and data were collected at more than 100 monitoring sites. To examine change in the recent past, we are collecting records and assembling databases concerning permafrost sites which had been examined by industrial and government partners during the past two decades. An indication of recent permafrost change was the loss of permafrost at half of the sites that we examined in August 2007 and 2008 along the Alaska Highway east of Whitehorse compared to conditions recorded by one of Canada's first permafrost scientists in 1964. Another finding is that permafrost in the mountains of the Yukon is warmer than we expected based on projections from standard climate stations, all of which are located in the valleys. In the cold, continuous permafrost at Herschel Island in northern Yukon, the ground has warmed by over 3°C in the 20th century, in close response to the warming of climate since 1899-1905. In the Mackenzie delta area, the mean annual ground temperature has increased by about 1.5°C since 1970 at sites in tundra regions, and less in the delta itself. In the delta, the influence of numerous water bodies reduces the impact of climate warming in winter on ground temperatures, as these lakes and channels do not all freeze through. In the uplands near Inuvik, ground temperatures are now sufficiently warm that changes to surface conditions may lead to permafrost degradation.
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