Jorgenson, M.T., Racine, C.H., Walters, J.C. and Osterkamp, T.E. 2001. Permafrost degradation and ecological changes associated with a warming climate in central Alaska. Climatic Change 48: 551-579.
What was done
The authors examined the extent, history and rates of permafrost degradation in the Tanana River valley lowlands of central Alaska over the past 300 years using a combination of methods, including repeat aerial photography (1949, 1978 and 1998), radiocarbon dating of organic material, and tree ring analyses.
What was learned
According to the authors, the "evidence indicates that nearly all the permafrost degradation has occurred since 1750 and that 83% of the degradation occurred before 1949." They also determined that 53% of the degradation occurred since 1850.
What it means
These results highlight another occasion where model projections do not match up with reality; for according to the climate alarmists, permafrost degradation in the planet's polar regions should be accelerating as a result of CO2-induced global warming. Yet, as the data show, half of the melting took place prior to 1850, and no scientist in their right mind would attribute this degradation to CO2-induced global warming, as atmospheric carbon dioxide concentrations varied little during this 100-year period (1750-1850).
A similar argument can be made with respect to the authors' finding that 83% of the permafrost degradation took place prior to 1949, for it is the second half of the 20th century that has seen the majority rise in anthropogenic CO2 emissions since pre-industrial times. Thus, little, if any, of the permafrost degradation that has occurred in this central Alaska region can be the result of CO2-induced global warming. Instead it must be a consequence of a combination of other important factors.