From KlimaNachrichten

By KlimaNachrichten Editor

We had already reported on the meteorological August and its previous months here and here. So now the entire summer on average according to the official DWD data, they always appear somewhat delayed.

The pure facts of the last 101 years:

The 18.3°C reached is already warm: There were only 9 years before that recorded higher values, of which only one (1947 with 18.5°C) before 1980. The increase after that is obvious. However, 2025 was a long way from the record (2003, still 1.4°C warmer). However, the past summer did not “feel” too warm. The reason is probably the 30-year smoothing (bold): There was only a slight up and down until about 1980, in the 30s to the mid-50s it was slightly warmer than in the 60s and 70s.

The probable reason for this: a natural fluctuation of the AMO, which influences the local summer temperatures, as has been known for some time. From 1975 to 1981 it was often clearly “too fresh” for this, the AMO switched to “negative”. “When will it be summer again?” wrote Rudi Carrell in 1975 and he was right at the time. Last year it was almost 2°C warmer on average, and yet the song experienced a “citation renaissance”.

Here, too, smoothing helps in the search for the reason: The “collective memory” changes with experience and hardly anyone remembers the weather longer than 30 years ago, even if they could. And 2025 was just below that! The fact that this smoothed average is now 2.4°C higher than at the time of the evergreen is beyond individual experience. The data doesn’t lie, and it ended up being warmer, but rather at the low end of the expectation range.

Precipitation can be kept shorter: in 75 previous years it was wetter, in 25 drier. The rain was “stinking normal” with around 219 mm. The harvest was quite good, contrary to fears in spring, sometimes quite dramatically formulated: “Germany is drying out“.

Some people probably called for subsidies for agriculture prematurely? One or the other also has to learn that water is in a cycle and is not “consumed”. What is evaporated sooner or later falls back to earth elsewhere as precipitation.

There is also no real long-term trend in precipitation, the 30-year smoothed course probably still points downhill at the end due to the really low values of 2018 (129 mm) and 2022 (143 mm).

Heat in Berlin or “Summer in the City”

The million-dollar hit of “Lovin’ Spoonfull” from 1966 has probably also made it into the “collective memory”. We had already looked at a value for “physiological heat” in the previous year (result at the time: not a hellish summer in 2024, it was still 2/10 °C warmer on average than this one) and for the last time at the beginning of July of the year.

Again, a brief explanation of this. How “hot” it is is not only determined by the maximum temperature of the day. We actively evaporate for cooling and this works much better with less humid air than with already more humid air. Eckart von Hirschhausen certainly learned this during his medical studies, “Human Physiology” is a compulsory subject. So why he suppresses the active cooling of humans (“alittle over 42°C outside denatures the brain“) probably remains only his secret.

A very efficient measure of humidity is the dew point. It is the temperature at which dew forms. If you cool a container with water (optionally also beer) with ice outdoors, you will eventually cause the vessel to fog up. If there is a lot of moisture in the air, this happens at a higher temperature than at a dry temperature.

The combination with the maximum temperatures is now done by simply adding the values day by day. This is added up and to distinguish real heat from only warm days, there is a limit: if the sum exceeds the value of 44°C, the difference between this threshold and the value reached is added up. So up to 44°C zero.

In a comparison of the years, this diagram is created:

It quickly becomes clear: In Berlin and the surrounding area (in the southwest of Germany it will look different, but the long-term observation for heat is only “local” and most people in a single city live in Berlin) the summer was only quite exactly in the average of the years 1981-2010 in terms of heat.

The only really serious heat wave lasted only from 12.8.-15.8. of the year. But then also crisp with up to 35°C maximum temperature and 18°C dew point on August 15th. Only all this did not last as long as e.g. in 2015 from August 2-15 and the “heat long-term effect” could hardly unfold. What did the inhabitants still experience in 2006 and 2019! In contrast, 2025 was literally “hypothermic”. And that’s exactly what was felt throughout July until the “mini heat wave” in mid-August. This raised the final value at least to the average 1981-2010.

Thus, by definition, the summer of 2025 is over. All in all: In the context of the last 30 years, it is by no means too warm or too dry. Will some media learn from this when “forecasts” with thick headlines (=clickbaits) are produced again, used for apocalyptic statements? The next winter is not far away and the countdown to crazy stuff about the weather is already on.