Climate change in India inferred from geothermal observations

Abstract

Temporal variations in surface ground temperature impart a signal to the subsurface thermal regime that is captured in borehole temperature‐depth profiles. Seventy temperature‐depth profiles in India, located between 12° and 28°N, are analyzed to infer past changes in ground temperature. These profiles exhibit predominantly positive anomalous temperatures relative to the background thermal regime beginning at depths of 75–150 m and increasing toward the surface. This pattern is consistent with warming over the past century. An interpretation in terms of linear surface temperature change indicates warming of about 0.9° ± 0.1°C over the past 150 years. Relatively complete surface air temperature (SAT) records from meteorological stations near the boreholes indicate similar rates of warming over the last century. A combined analysis of borehole temperatures and SAT records yields a long‐term, preobservational mean temperature, 0.8° ± 0.1°C lower than the 1961–1990 mean SAT. When the most recent decade is included directly in the analysis, the average total warming in India from the early 1800s to the late 1990s is ∼1.2°C.