CLIMATE-CHANGE INFERRED FROM BOREHOLE TEMPERATURES

Temperature changes at the Earth's surface propagate downward into the subsurface and impart a thermal signature to the rocks that can be an alyzed to yield a surface temperature history over the past few centur ies. Thus subsurface temperatures have the potential to extend the 20t h century meteorologic temperature record back well into the pre-indus trial era and therefore to provide information relevant to an assessme nt of the role of greenhouse gases in atmospheric warming. Short perio d variations in surface temperature are attenuated at shallow depths, whereas longer period excursions propagate deeper. The ability to reso lve details of the surface temperature history diminishes with time. C are must be taken to identify and evaluate local anthropogenic tempera ture perturbations such as urbanization, deforestation and wetland des truction and microclimatic effects associated with topography and vege tation patterns, in order to isolate true regional climate change. Inv estigations in North America indicate significant regional variability in the surface temperature history inferred from borehole profiles, s imilar to that observed in the meteorologic record of the 20th century .