Figure 7.3 shows the history of the annual average temperature since climate records began on January 1, 1893, up to the end of 2013. In addition to some natural fluctuations, it can also be discerned that the annual mean temperature rises significantly over the course of the measured last 120 years. Whereas in the early measurement years the annual mean temperature was around 8 °C , in recent years average values between 9.5 and 10.5 °C were usually reached. This temperature rise is also illustrated by the trend line.
With an average temperature of 8.85 °C over the entire period, the Potsdam station exhibits the lowest temperature of all stations compared. Besides the peripheral location, which was not subject to significant changes due to construction in its surroundings, a reason for this lies in the long measurement series of 120 years, which also includes temperature values that have not yet been influenced by anthropogenic climate change.
Figure 7.4 shows the histories of the threshold days summer day, hot day and tropical night. The individual trend lines for summer days and hot days illustrate the increase in threshold days in the measurement period. Whereas the number of summer days was 34 per year in 1893, in the trend it increased by 16 to 50 days per year in 2013.
In the development of the hot days, the increase in the case numbers is naturally slowed down and amounts to 3 days in the trend over the entire measurement period. However, here, too, significant fluctuations are observed in the course of the 120 measurement years. With 26 days, the year 1947 recorded the most hot days. With respect to the tropical nights, a clustering in the current decade can be observed.