Large ground surface temperature changes of the last three centuries inferred from borehole temperatures in the Southern Canadian Prairies, Saskatchewan

New temperature logs in wells located in the grassland ecozone in the South ern Canadian Prairies in Saskatchewan, where surface disturbance is conside red minor, show a large curvature in the upper 100 m. The character of this curvature is consistent with ground surface temperature (GST) warming in t he 20th century. Repetition of precise temperature logs in southern Saskatc hewan (years 1986 and 1997) shows the conductive nature of warming of the S ubsurface sediments. The magnitude of surface temperature change during tha t time (11 years) is high (0.3-0.4 degrees C), To assess the conductive nat ure of temperature variations at the grassland surface interface, several p recise air and soil temperature time series in the southern Canadian Prairi es (1965-1995) were analyzed. The combined anomalies correlated at 0.85. Ap plication of the functional space inversion (FSI) technique with the boreho le temperature logs and site-specific lithology indicates a warming to date of approximately 2.5 degrees C since a minimum in the late 18th century to mid 19th century. This warming represents an approximate increase from 4 d egrees C around 1850 to 6.5 degrees C today. The significance of this recor d is that it suggests almost half of the warming occurred prior to 1900, be fore dramatic build up of atmospheric green house gases. This result correl ates well with the proxy record of climatic change further to the north, be yond the Arctic Circle [Overpeck, J., Hughen, K., Hardy, D., Bradley, R,, C ase, R., Douglas, M,, Finney, B., Gajewski, K., Jacoby, G., Jennings, A., L amourex, S., Lasca, A., MacDonald, G., Moore, J., Retelle, M., Smith, S., W olfe, A., Zielinski, G., 1997. Arctic environmental change of the last four centuries, Science 278, 1251-1256.]. (C) 1999 Elsevier Science B.V. All ri ghts reserved.