The temperature distribution in the upper layers of the crust is determined by the density of the heat flow from the Earth interior and temperature distribution at its surface. On the geothermograms in the 0 to 500 depth range, we can see temperature variations for the period of 1000 years or more. Based on the solution of an inverse problem of thermal conductivity, we have estimated regional and local temperature fluctuations at the Earth's surface from geothermal data and make conclusion about the climate changes in Ukraine in the second millennium. The results of the solution of the inverse problem are compared with the meteorological observation data.