Effect of Climate Change on Permafrost in Alaska and Siberia:
Short-Term (Decadal) Variability and Long-Term (Millennial) Changes.
Permafrost, in general, is a product of cold climates, which are typical for high latitudes or high elevations. Hence, the air temperature is one of the most important parameters, which determine the existence of permafrost and its stability. However, because of the effects of intervening snow cover, vegetation, and active layer and because of the effects of possible changes in other climatic variables, particularly precipitation, somewhat different changes are generated at the surface of permafrost. Our recent study shows that permafrost temperatures reflect changes in air temperatures over a long time scale (decadal and longer) very well and much better than interannual air temperature fluctuations. The recent climate warming brought soil temperatures at the North Slope of Alaska sites to a surprisingly high level, about 3°C warmer than long-term averages. In Interior Alaska recent permafrost temperatures are 1°C to 1.5°C warmer than they were in the 1970s. At the same time, comparison between borehole temperature measurements in Barrow from the 1950s and recently measured temperatures at the same boreholes shows a significant similarity in the temperature profiles within the upper 20 meters of permafrost. Application of our calibrated numerical model shows that measured 1°C difference at 15 meters in permafrost temperatures between 1950 and 2001 is the result of very recent warming during the late 1990s. Much colder permafrost temperatures (up to 2 to 3°C colder) were typical for Barrow during 1970s. That investigation was based on application of our high-resolution numerical model using the Barrow National Weather Service climate data and employing a “permafrost temperature reanalysis”. Very similar permafrost temperature history was reconstructed for East Siberia.
In the long-term perspective, the recent climate is somewhat cooler than it was during the Holocene Optimum (six to eight thousands years ago in Alaska). However, there is much evidence based on proxy climatic data, that the climate in 1980s and 1990s was the warmest during the last millennium. Moreover, several researchers reported thawing of permafrost from the surface at several undisturbed locations in Alaska. It is important from the ecological and engineering point of view to understand what is the age of this recently thawing permafrost.