SEPARATION OF ANTHROPOGENIC CLIMATE FORCING FROM NATURAL CLIMATE VARIABILITY

Achieving coherence among the different methods and data used to determine climate trends is critical to meeting the challenge of separately identifying and quantifying anthropogenic forcing and natural climate variability. We have approached the problem using a synthesis of meteorological data, solar radiation information and data, and borehole temperature data representing time scales of decades to centuries. Our basic hypothesis is that changes in ground energy storage correlate with changes in the radiative forcing signal. If variation in ground energy storage, meteorological data, and radiation data can be correlated over decades, it should be possible to use the longer time-scale of borehole data to infer longer time scale changes in climate forcing. We have tested this hypothesis by synthesis of daily meteorological data from an array of 89 automated meteorological stations with the TOA composite solar irradiance and repeat measurements of T-z profiles in boreholes initially logged ten to twenty-six years ago. We calculated ground energy storage during the time between temperature measurements and found good correlations with both the TOA solar irradiance and the SAT and soil temperatures at the meteorological stations. The significant findings to date are: 1) through use of a thermal diffusion filter, we detected a close correspondence between the SAT, soil temperatures and TOA irradiance during the past two solar cycles; 2) Repeat temperature vs. depth measurements at a number of borehole sites over a 22 year period indicate that changes in borehole temperatures closely agree with changes in surface air temperatures and soil temperatures on multi-decade timescales. We are extending the study to century scale with an array of 40 boreholes sites and 161 meteorological sites covering Kansas, Nebraska, South Dakota, North Dakota, Alberta, Saskatchewan, Manitoba and Ontario.