Global warming became the reality. The rate and duration of warming in the 20th century is probably the biggest within the last 1000 years (about 0.6 K from 1861). In the Northern hemisphere the 1991 – 2000 decade was the warmest of the last millennium. The year 1998 was globally the warmest and 2002 the second warmest since the beginning of climatologic observations. The temperature trend in Slovakia is analogous to the global one, since 1901 the warming has reached a level of about 1.1 K. Climate system variability has not changed significantly. This paper discusses the estimation of sufficiently exact thermal parameters for the heating season in Slovakia, mainly in conditions anticipated during the first decades of the 21st century. Data from 32 climatologic stations during the period of 1961 2003 have been used.