North American Ground Surface Temperature Histories: A Contribution to the PAGES2k North American Project

Abstract:

Within the framework of the PAGES NorthAmerica2k project, three hundred and seventy three (373) North American temperature-depth profiles from boreholes deeper than 300 meters were analyzed for recent climate. To facilitate comparisons and examine the same time period, the profiles were truncated at 300 m. The ground surface temperature (GST) histories for the last 500 years were inverted from the subsurface temperature anomalies using singular value decomposition for a model of 10 temperature changes along time-intervals of increasing duration. The inversion retains four singular values and accounts for the data acquisition time difference. The reference surface temperature and geothermal gradient were estimated by linear regression to the deepest 100 meters with a 95% confidence interval. Additionally, a Monte-Carlo method was used to find the range of solutions within a maximum subsurface anomaly error determined by the root mean square between the model and the data. The GST history results for North America, given by the mean and 95% confidence interval, reveal in most cases, a warming up to 1°C - 2.5°C during the last 100-150 years.