Inferring Climate Change from Underground Temperatures: Apparent Climatic Stability and Apparent Climatic Warming

Abstract

Data are used to demonstrate two effects apparent in ground surface temperature histories coming from inversions of borehole temperatures: apparent climatic warming and apparent climatic stability. Unrecognized local terrain effects, such as spatial or temporal change in land cover, cause warming locally. Where there is seasonally frozen ground, the ground temperature is not coupled to freezing air temperatures due to both latent heat of moisture in the ground and snow cover. Consequently, average ground temperatures can be much warmer than average air temperatures, and changes in average air temperatures result in much smaller changes in average ground temperatures. This produces apparent climatic stability when past air temperatures are inferred from borehole temperatures. However, increases in summer air temperatures, such as those due to deforestation, are well coupled to the ground temperature, causing the average ground surface temperature to increase, even in colder climates.