Climate change inferred from borehole temperatures

Abstract

Temperature changes at the Earth's surface propagate downward into the subsurface and impart a thermal signature to the rocks that can be analyzed to yield a surface temperature history over the past few centuries. Thus subsurface temperatures have the potential to extend the 20th century meteorologic temperature record back well into the pre-industrial era and therefore to provide information relevant to an assessment of the role of greenhouse gases in atmospheric warming. Short period variations in surface temperature are attenuated at shallow depths, whereas longer period excursions propagate deeper. The ability to resolve details of the surface temperature history diminishes with time. Care must be taken to identify and evaluate local anthropogenic temperature perturbations such as urbanization, deforestation and wetland destruction and microclimatic effects associated with topography and vegetation patterns, in order to isolate true regional climate change. Investigations in North America indicate significant regional variability in the surface temperature history inferred from borehole profiles, similar to that observed in the meteorologic record of the 20th century.