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 surf ace temperature (GST) history, reflecting past climate conditions, can be evaluated by analysing the excursions left on the present-day temp erature-depth distribution measured by precise temperature leggings in the boreholes. Temperature logs from fifteen selected holes were inve rted into GST histories to assess the corresponding climatic changes. These temperature records generally represent typical conditions exist ing on the territory of the Czech Republic. In combination with the GS T reconstructions from our previous works, these data were used to ass ess the regional pattern of the last 250-year climatic change. The GST s were obtained by applying the generalized least-squares inversion me thod [Jackson, D.D., 1972. Interpretation of inaccurate, insufficient and inconsistent data. Geophys. J. R. Astron. Sec. 28, 97-109], whereb y 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 l ast 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 recen t warming rate may indicate an impact of human activities. The verific ation of the GST assessment was accomplished by the independent past c limate reconstructions gained by the use of historical sources and ins trumental records. (C) 1998 Elsevier Science B.V. All rights reserved.