Agroclimatic elaborations, including practical agricultural recommendations, are based on recent climate standards (30-year periods): 1881-1930, 1931-60, 1951-80, and 1961-90. The period 1971-2000 has just recently been included in climate studies. During the final two decades of the 20^th century and in the beginning of the 21^st century we have observed a clear and well documented increase in air temperature. In this article the authors compare the extent of thermal regions in Poland, which have been designated on the basis of effective temperature sums ≥10ºC for the period 1971-2000. It should be noted that at present this is the effective climatological standard and it was used to obtain regression equation data for 2000 and 2007. The results of this study indicate that the area of the temperate-cool region with effective temperature sums ≥10ºC in the range of 2,000-2,400ºC has been decreasing in subsequent time periods – 37%, 12%, and 3%, respectively. Meanwhile, the warm region characterized by effective temperature sums in the range 2,800-3,200ºC has increased its area from 3% in 2000 to 26% in 2007. It should be emphasized that the warm region has not been observed when we analyzed the 1971-2000 data. The originality of this article is outlined by the fact that it documents and characterizes contemporary climate changes, which are manifested through changes in the extent of thermal regions. In addition, this article attempts to depict a number of consequences of these changes by illustrating the possibility of expansion of the surface area of thermophilic plants.