Comparisons of borehole temperature-depth profiles and surface air temperatures in the northern plains of the USA

Temperature-depth profiles measured in boreholes contain a record of temperature changes at the Earth's surface. The degree to which these profiles and surface air temperature records track each other is quantitatively assessed for the northern plains of the USA. Surface air temperature records are used as a forcing function to generate synthetic transient temperature profiles which are compared with transient temperatures derived from borehole temperature-depth data. These comparisons indicate that surface air and ground temperatures are correlated. Furthermore, these comparisons yield a long-term mean temperature tied to the meteorological record which provides a context for interpreting contemporary warming trends. Our results indicate that warming recorded in surface air temperature time series represents a positive departure above baseline temperature estimates.