The present paper has provided some information on the long-term evolution of the temperature field in permafrost of Siberia. During the Late Pleistocene the southern permafrost border reached 48-49° N. During the Holocene the permafrost area has decreased and this process continues today. The permafrost decay may be intensified due to global climate warming in the 21st century. Regime temperature measurements at meteorological stations confirm an increase in the air temperature of Siberia during the last 40-50 years (average rate 0.04 °C/year). If modern trends are preserved then the surface temperature may increase by 1.2-2 °C by 2050. The southern border of continuous permafrost may be moved to the north by hundreds of kilometres. Numerical modeling of the permafrost temperature field has shown that an increase in Ts (ground surface temperature) will result in the formation of significant temperature anomalies in the upper rock layer, as can easily be seen with temperature monitoring techniques. In the far north regions values of Ts will remain negative up to the end of the 21st century and the permafrost will not start to decay. Here the only process will be an increase in the temperature of the frozen rocks (within the depth interval 0-260 m) due to conductive heat transfer, but no phase transition processes. In contrast in non-stationary permafrost blocks the upper permafrost layer (upper 12-17 m) will undergo thawing by 2100. Further analysis is required to better quantify estimations of the discussed thermal processes in permafrost. But one important process clearly shown in this paper is that fast thawing in the upper layer of frozen ground will occur in the case of climate warming. This process is rather serious as it may cause destructive influence on all engineering constructions: pipelines, roads, petroleum and gas stations and other buildings. Also permafrost decay will promote the release of natural or human-sequestered gases (CO2, CH4) preserved in frozen rocks.

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