Good day My name is Peter Hoffmann and I have been working at PIK in the Hydroclimatic Risks working group since 2012. My focus is on regional climate change and changes in meteorological phenomena. Europe is the continent that is warming the fastest. There are diverse factors for this (contrasts, aerosols, dynamics). This also has direct impacts on the intensification of heatwaves.
This brings me to the actual topic, the phenomenon of heatwaves. Here you see the synoptic weather situation that led to record temperatures in Western Europe at the end of June. It has an Omega shape that blocks the Atlantic inflow. This clears the way for the inflow of extremely hot air masses from the south. The weather was accordingly hot and dry in many parts of the country. It makes clear that local weather phenomena usually have a large-scale context.
The effects were also noticeable locally. The figure here shows the temperature variability over the last two years relative to a climatic context of the 1961–1990 period. The resulting temperature anomalies can be presented relative to the mean annual cycle. The dominance of positive anomalies is clearly recognizable. On average, this results in an anomaly of nearly 2°C. The highest anomaly of almost 10 degrees falls on the date of the prominent heatwave at the end of June 2026.
To compare temperature conditions, climate research uses probability distributions. They take the shape of a Gaussian distribution. In a warmer climate, the distribution is shifted toward higher values. Looking at the right tail of the distribution, this means a higher probability for extreme values. Not only that. The climatic shift of the distribution also changes weather variability. Indirect effects play an important role here, triggered significantly by dynamic factors. Weather variability increases because the moderate weather influence from the North Atlantic is blocked more frequently than before.
Using the Potsdam climate measurement series since 1893 as an example, the development of annual maximum temperatures can be well illustrated. While values before 1960 were well below 38°C, we see a cluster of values above that in recent decades. A matter of time until 40 degrees is exceeded. In 2026, the time had come. The old record was clearly shattered.
There was sufficient time to prepare for such a weather event. Almost a week prior, the development of the heat period was already foreseeable. Immediately beforehand, forecasts became even more precise. It could have been even more intense.
Looking at long-term correlations of climatological indicators, it becomes clear that with every degree of mean temperature rise, extreme days also increase. Learning from the past means that in the case of Potsdam, 5 hot days are added when the mean annual temperature rises by 1 degree. Considering only recent decades, it could be even more. Added to this is the growing dispersion of values.
Similar relationships are recognizable when considering indicators that also account for heat perception. This includes the Humidex, which also considers humidity conditions. Because the muggier it feels, the harder it is for the body to regulate its heat balance. One thing becomes clear: regardless of the indicator, heat stress on humans increases with rising mean temperature.
<small> ### **Statistical & Absolute Metrics** * Absolutely measured peak temperature values (41.8°C – 27 June 2026 – Saxony-Anhalt) * Defined thresholds (Germany average approx. 22 hot days) * Location-specific rarity values ($T_{max}$ and $T_{min}$ were in the 99th percentile range at the end of June) * Temporal deviation from normal state (Daily mean anomaly was +10 K) ### **Temporal & Spatial Dynamics** * Temporal duration and persistence ($T_{min}$=29.4°C in Saxony) * Geographic extent * Natural variability and trends * Statistical return period (Extreme values of > 41°C in Germany have return intervals of >> 100 years) ### **Impact & Climate Relation** * Actual impact of heat on the human body * Amplification magnitude due to anthropogenic factors </small>
Heatwaves belong to large-scale phenomena. Unlike heavy rain, they are usually supra-regional and can last for days to weeks. Unlike heavy rain or storms, the stress threshold remains elevated longer. Drought development can even extend over years when below-average rain and high evaporation rates coincide.
Characteristic temperature patterns are linked to the corresponding weather pattern, reinforced by the transport of air masses. In the case of an Omega pattern, hot air masses flow far north from the Mediterranean region in summer on the rear side. The higher the mean temperatures, the more intense heatwaves can become. Slight shifts in position can affect neighboring regions.
Heatwaves triggered by high-pressure weather patterns are part of natural weather variability. In mid-latitudes, the westerly wind influence from the North Atlantic dominates. It prevents stable high-pressure systems from building up into dangerous heatwaves in summer. Cold air masses then remain in the north and warm air masses in the south.
Climate change creates warming contrasts that indirectly affect weather variability. The jet stream is known to be sensitive to this. Because when the gradient between the pole and the equator decreases, it slows down the dominant westerly wind influence. As a result, weather patterns can persist longer, especially in summer. Heatwaves can thereby build up dangerously and intensify.
Already today, we observe more frequently that the influence from the North Atlantic is blocked. In connection with this, air mass transport across latitudes and climate zones is initiated more often. This leads to cold air masses breaking out to the south and warm air masses pushing far to the north. This favors weather extremes.
What foreseeable consequences does this have for us? Let's compare the distribution of hot days in the past and present. 1. The mean value has doubled. 2. The distribution today is shifted, significantly broader, and open at the upper end. 3. Cannot be explained by the temperature effect alone. 4. The summer of 2026 marks the current maximum value of the distribution.
The heatwave at the end of June ranked 5th compared to historical heatwaves in Europe in terms of duration, intensity, and surface area. All heatwaves after 2001 are marked in orange. Before that, only 3 heatwaves out of a total of 25 met the criterion. Deviations of over 10 degrees compared to normal conditions lasted almost two weeks.
It is the interplay of various effects that shapes the extent of heatwaves. Climatological: higher mean values as a baseline Meteorological: critical weather patterns controlling the inflow from the south Early heatwaves often hit us in everyday life: at work, in school, and not on vacation.
Analog scenarios illustrate the changing conditions associated with specific weather patterns. Such as the heatwave of June 2026. The manifestations would have been far more moderate in the past. The rise in extremes can significantly exceed that of mean values. This is what makes heatwaves so dangerous.
The nature of heatwaves over Europe is foreseeably changing. This demands adaptation to protect human health. The adaptation matrix combines current knowledge levels: 1. How is the phenomenon changing? (Climate) 2. How relevant are the changes? (Health) 3. How great is the need for adaptation? The goal must be to increase resilience against the phenomenon.
Climate services represent an important basis for raising awareness among decision-makers regarding the relevance of changes. For more than 10 years, we have operated such a system for various regions and sectors. Results from ongoing projects within research departments are integrated into the portal.
The development of indicators across various sectors for potential development scenarios up to 2100 is presented. Using hot days as an example, conditions can be displayed and compared locally to regionally. The summer of 2026 lies at the upper bound of present-day conditions.
15 hot days in Lower Saxony are conditions expected further south. A few years ago, the Federal Environment Agency (UBA) conducted a twin city analysis. They looked at how cities in Germany have already shifted climatically when comparing them with earlier climate conditions in other regions. Berlin has already shifted significantly to the southwest. The shift continues with every tenth of a degree.
In a few years, Berlin's climate could correspond to the climatic conditions of Paris in the 1960s to 1990s. Not only on average, but also regarding extremes.
The combination of hot days and tropical nights would gain higher relevance when apartments and rooms heat up for days because there is no noticeable cooling at night. Conditions we previously knew mostly from holiday destinations. Not only vulnerable groups are affected; healthy individuals also experience reduced productivity.
I would like to point out one special feature. Even if the RCP8.5 scenario is currently considered less likely, it is still advisable to keep it as a stress-test scenario. Because current observations are sometimes stronger in magnitude than in simulation data.
Without man-made climate change, the 2026 heatwave probably would not have occurred. Adaptation to the consequences. Mitigation of further development. Higher resilience through structural heat protection measures. Greening, shading, ventilation, facades and roofs, air conditioning systems. Intelligent building management.
Beyond structural heat protection measures, social aspects can also mitigate heat stress. And that is the environment in which we move and the people who surround us.
Synoptic weather patterns shape our local weather conditions. From historical data, we can derive manifold relationships that provide important orientation when dealing with critical weather conditions.