The study discusses changes in the average annual air temperature over Europe in the years 1931–2020. The results of the research show that in 1987–1989, there was a sudden change in the thermal regime over Europe and a discontinuity appeared in the course of this climatic element. In the years 1931–1988, despite the high inter-annual variability, the temperature trend was zero. A positive, statistically significant, temperature trend appeared after 1988. The entire warming in Europe, which can be estimated at ~2.3 deg, occurred after 1988. The discontinuity in the course was caused by an abrupt change in macro-circulation conditions in the Atlantic-Eurasian circulation sector, which manifests itself as a fundamental change in the frequency of the macrotypes of the mid-tropospheric circulation (500 hPa) according to the Wangengejm-Girs classification, causing an equally fundamental change in the weather structure. The change in macro-circulation conditions was forced by a change in the thermal state of the North Atlantic – a sharp increase in the intensity of oceanic heat transport to the north. The analysis showed that the annual variability of temperature over Europe was mainly influenced by natural processes, the variability of which explains ~65% of its variance. Radiative forcing, which is a function of anthropogenic increase in CO2 concentration in the atmosphere, explains only 7–8% of the variability of the average annual temperature over Europe, being a secondary or tertiary factor in shaping its changes.

Hot or warm extremes are days with exceptionally high air temperatures in a given place and/or season. They may have significant impacts on human health and life, the natural environment, and the economy. The global rise in near-surface air temperatures translates into increases in the frequency, intensity, and duration of such events, which contributes to the intensive development of research on them. This review aims to summarize the state of knowledge of hot and warm extremes in Europe, with a special focus on their definitions, physical drivers and impacts, long-term variability and trends. The study demonstrates that research on temperature extremes is making remarkable progress, but there are still issues to be explored to understand these complex events.

The growing season length indices derived from air temperature are frequently used in climate monitoring applications as well as to predict the response of forest ecosystems to climate change. The indicator most widely used in the studies of forest ecosystems is the length of the thermal growing season (temp ≥5°C), less commonly the parameters of the forest growing season (temp ≥10°C). However, only a few studies used long-term series of temperature measurements in the forest. In this article, we determined the temporal changes in the parameters of the thermal (TGS) and forest (FGS) growing season in the Experimental Forests of the Warsaw University of Life Sciences in Rogów (51o40’N, 19o55’E, h = 194 m MSL) in the years 1951–2020. The analysis is based on the dataset (daily mean air temperature) obtained from a meteorological station located near the forest complex and from a forest under-canopy station located in a more than 120-year-old fresh mixed forest. The results show a significant extension of the growing season in 1951–2020, the TGS lasted on average 2.8 days/10 years, and the FGS 2.4 days/10 years. The extension of the TGS and FGS was a consequence of both its earlier start and later end. The start of the TGS was characterized by a statistically significant negative trend (1.3 days/10 years), and most changes were characteristic for the last three decades (4.4 days/10 years). The last 30 years were also characterized by a statistically significant trend towards the later end of the TGS. The TGS in 1991–2020 was longer than in 1951–1980 and 1971–2000 by 9 days, while in 1981–2010 by 5 days. Changes in the length of the TGS resulted primarily from its earlier beginning: in the multi-year period 1991–2020, the TGS started 7 days earlier than in 1951–1980. In the case of the FGS, these changes were weaker, although there was a statistically significant negative trend in the start dates and a positive trend in the FGS length. The FGS started almost a month later than the TGS (average on April 28) and ended 4 weeks earlier (average on October 5) and lasted 160 days. TGS in the forest was shorter than outside the forest by 3 days, and FGS by 1 day. The acceleration of the beginning of TGS during the last three decades was faster than the beginning of the frost-free period, indicating a possible increase in vegetation exposure to spring frost. This may pose a threat to the development of plants in the first phase of vegetation.

Based on climatological data from 1901–2020 from the Research Station of the Department of Climatology of the Institute of Geography and Spatial Management of the Jagiellonian University in Krakow, the multi-year course of selected elements of Krakow climate was characterised and the role of local spatial development plans was indicated in terms of minimising the effects of the urban heat island and global warming.

The aim of the study is to present changes in air humidity in central Poland in the years 1966–2000 in Łódź as an example. The values of air temperature, relative humidity and atmospheric pressure from four observation terms, 00, 06, 12 and 18 UTC, were used. On this basis, the saturated vapour pressure, the current vapour pressure, and the saturation deficit were calculated. Then, the variability of these three indicators and relative humidity was examined. The variability of monthly and seasonal average values of humidity indices in four observation periods was presented, the trends in seasonal variability of humidity indices were calculated and the distribution functions of their distributions were compared in the midday period in three 15-year periods: 1966–1980, 1986–2000 and 2006–2020. It has been shown that the pressure of saturated water vapour is the highest in summer, the lowest in winter, and slightly higher in spring than in autumn at all times, except for the night. It increased significantly in the studied period as a result of the increase in air temperature. A comparison of the distributions in three 15-year periods shows a significant increase in the probability of occurrence of high values of saturation vapour pressure, even above 30hPa. The water vapour pressure in the air is highest in summer and lowest in winter, but in spring it is lower than in autumn. All trend coefficients are positive, but only less than half are statistically significant. A comparison of the distributions over three 15-year periods show a slight increase in the probability of higher values of the actual vapour pressure. The saturation deficit, as the difference between the previous two indicators, increases significantly. Its value in spring is significantly higher than in autumn. The trend is positive, especially in spring and summer, and the comparison of distributions shows that in the last 15 years the probability of high values of saturation deficit increased significantly. The course of relative humidity is the opposite of saturation deficit. In autumn, the relative humidity is definitely higher than in spring. The trend is down. To sum up, warming brings an increase in the capacity of the atmosphere for water vapour, a slight increase in the amount of water vapour in the air, but also a significant increase in saturation deficit and a decrease in relative humidity, which is particularly strong in spring in the first half of the growing season.