Introduction Jacek Majorowicz 1,2, Walter Skinner 3, William Gosnold 2 and Jan Safanda 4 1 Northern Geothermal, 105 Carlson Close, Edmonton, Alberta, T6R 2J8, Canada, Phone/Fax: University of North Dakota, Grand Forks, North Dakota, USA 3 Climate Research Division, Environment Canada, Toronto, Ontario, Canada 4 Institute of Geophysics, Bocni II, Prague, Czech Republic Heat energy gain over the past two decades in the Canadian Prairies from repeated borehole temperature logs Temperature depth profiles ( > 150m) in the Canadian Prairie and U.S.A northern Great Plains region have been interpreted to infer a very strong ground surface temperature (GST) warming over the past 100 years of 1 - 4ºC. In the grassland areas of this region, the GST increases are comparable to surface air temperature (SAT) change from meteorological records. Temperature-logs in boreholes, initially made one to two decades ago, in the Canadian Prairies and U.S.A northern Great Plains were recently repeated. Jacek Majorowicz Jan Safanda, Measured versus Simulated Transients of Temperature Logs - a Test of Borehole Climatology. Journal of Geophysics and Engineering 2(4): , Jacek Majorowicz, Walter Skinner, Jan Safanda Will Gosnold, Differences between repeated borehole temperature logs in the southern Canadian Prairies-validating borehole climatology. Clim. Past Discuss. 2: 1–30, Heinle Shannon Will Gosnold, New Measurements from Old Boreholes: A Look at Interaction Between Surface Air Temperature and Ground Surface Temperature. Eos Trans. AGU, 88(52), Fall Meet. Suppl., Abstract PP11A-0216, 2007 There has been a distinct increase in western Canadian surface air temperature (SAT) over the past 100 years. The above time series represents the average curve of several annual SAT anomaly records in the Prairie Climate Region of western Canada. Temperature logs from deep boreholes, such as the example shown here in southern Alberta, can be used to estimate ground warming over time periods spanning decades to centuries. Repeated logs of temperature with depth (time) show anomalous curvature in the upper 100 m and progressive warming of the subsurface with time as shown in upper two panels in the next figure. The T-z transients forced by SAT match the observed T-z transient from repeated log data (see below example of well TSa13). Repeated borehole logging allows for the extraction of temperature differences over time such as those shown for the wells located at the Alberta-Montana border (see location map). Modeling of the effects of SAT change on the subsurface temperature regime shows that SAT variability is the primary forcing mechanism for the observed underground anomalous temperature with depth profile and observed change in temperature over time. The magnitude of heat storage is calculated for the last 100 years, and the last 1-2 decades, based on 40 individual well sites (some with multiple boreholes) having 51 temperature–depth logs in the Canadian Prairies and for 5 repeated logs (last 1-2 decades). Temperature transients vs. depth are shown below. The heat needed to warm the vertical column with a cross-section of 1 m 2 in the depth interval 20 – 150 m for the Canadian Prairies is 1.9E08 J. The change in heat energy flux in Watts/m 3 vs. depth is shown below. The change calculated from repeated logs is compatible (TSa13), mainly higher than change calculated from all 51 single temperature logs in Alberta and Saskatchewan, Canada The synthetic T-z transients forced by SAT – POM (surface air temperature – pre observational mean level) match the observed T-z transient data from repeated logs, while solar forcing based T-z transients explain only a small portion of observed underground heat gain. This demonstrates that the large heat gain by the ground cannot be fully explained by changes in solar forcing. Other factors, such as greenhouse gas forcing are likely responsible. SAT forcing is primarily responsible for the underground temperature changes diffusing with depth. Solar forcing - climatic surface forcing at assumed sensitivities can only account for the fraction of the last 100 years warming registered underground by 51 Prairie logs from 40 wells. The discrepancy between solar based T-z transients calculated in this paper and those observed from well logs begin at about 100m which we relate to the last 5 decades +/- 10 years. This is equivalent to the timing of increased warming due to other factors. The most likely factor is the dramatic increase in greenhouse gases. Summary Data, Method and Results Financial support 2007 – 2008 in part by: Surface warming of this magnitude causes the Earth to store large amount of heat. Observed anomalies of temperature with depth show that large amounts of heat have been stored underground. SAT variability, and the pre-observational SAT minimum related to the Little Ice Age (LIA) from the 17th to 19th centuries, are largely responsible for the large ground surface temperature (GST) warming trends and closely parallel SAT trends recorded at nearby meteorological stations but significantly diverge from the trends in top of atmosphere (TOA) solar irradiance.