Last 250 years climate reconstruction inferred from geothermal measurements in the Czech Republic

The subsurface of the Earth has a certain capability to remember what has happened on its surface tens to hundreds of years ago. Ground surface temperature (GST) history, reflecting past climate conditions, can be evaluated by analysing the excursions left on the present-day temperature-depth distribution measured by precise temperature leggings in the boreholes. Temperature logs from fifteen selected holes were inverted into GST histories to assess the corresponding climatic changes. These temperature records generally represent typical conditions existing on the territory of the Czech Republic. In combination with the GST reconstructions from our previous works, these data were used to assess the regional pattern of the last 250-year climatic change. The GSTs were obtained by applying the generalized least-squares inversion method [Jackson, D.D., 1972. Interpretation of inaccurate, insufficient and inconsistent data. Geophys. J. R. Astron. Sec. 28, 97-109], whereby the additional information on interdependence of both measured data and climate changes can be incorporated into the model in the form of covariance matrices. Three main episodes can be distinguished in the last 250 years: a warm period between 1790 and 1830, a slightly colder period in 1940-1960, and a general warming with the average rates of 0.01-0.03 K/year since then. The geographical distribution of the recent warming rate may indicate an impact of human activities. The verification of the GST assessment was accomplished by the independent past climate reconstructions gained by the use of historical sources and instrumental records. (C) 1998 Elsevier Science B.V. All rights reserved.