Reconstruction of the Past Climate in Southern Portugal from Geothermal Data

The study of the past climate in the territory of mainland Portugal using geothermal data started in 1996. From an initial set of about 90 temperature logs obtained Portugal, eight were chosen as good for estimating ground surface temperature (GST) in the past. The main results from the analysis of the collected geothermal data show, on average, that there has been an increase of the atmosphere mean surface temperature of about 1 K since the middle of the nineteenth century. This conclusion agrees with the results obtained from the analysis of air temperature records that were obtained in the Lisbon weather station since 1856. With the objective of improving the reconstruction of GST history in Portugal one of the eight wells (the TGQC-1 well) was cased and is being used for repeated temperature logging since 1997. The results of the temperature measurements repetition indicate that the warming trend continues to the present day, accelerating in the last 10 to 15 years. Since 2005 a geothermal climate change observatory was installed in the TGQC-1 well to study the air-ground coupling.