The heat wave is coming: temperatures of up to 40 degrees are expected in the next few days. But does this really have anything to do with climate change? There used to be hot summers. From research comes a clear answer.
It has already reached large parts of Europe – now the historic heat wave is also coming to Germany. Especially in the west and south-west of the republic it will be scorching hot, in North Rhine-Westphalia, for example, temperatures of up to 40 degrees are expected on Tuesday. The metropolises of Cologne and Frankfurt can adjust to 39 degrees, the German Weather Service (DWD) predicted on Monday.
A look at other European countries shows what can blossom for us. In British hospitals, operations had to be postponed because the temperatures in the operating theaters were up to 41 degrees. Flights could no longer take off from the largest British air force base, Brize Norton – parts of the runway had melted. And in Spain, at least two people have died in forest fires. “Climate change kills,” said Prime Minister Pedro Sanchez on Monday.
But is this really climate change? Or are heat waves with temperatures of up to 40 degrees not quite normal in summer? There are many voices from the usual spectrum on social media who accuse the media and politicians of senseless scaremongering. “They used to call it summer, now they color the weather map red and call it the climate crisis,” says a picture that is currently making the rounds on Facebook. Have we just gotten hysterical?
And indeed: hot temperatures were measured in Germany decades ago. In Bremen, for example, temperatures of 36 degrees are guaranteed for August 1943. In Cologne it was 37.9 degrees in June 1947, Potsdam even reported 38.4 degrees in July 1959.
But if you look at the long-term developments, you will quickly discover a trend. The German Weather Service (DWD) counts the so-called “heat days” for all German regions every year, i.e. days when it got hotter than 30 degrees. And in almost all regions, apart from areas like the Zugspitze, the number of hot days has increased significantly over the past 60 years.
The statistical outliers are therefore becoming significantly more frequent. Such a rapid increase within a few decades also refutes the claim that this is a completely natural temperature change on earth. Such changes do exist, but on this scale they occur much more slowly, more often over the course of centuries.
This is also consistent with the fact that average temperatures have increased rapidly. According to the DWD, the average annual air temperature in Germany rose by 1.6 degrees between 1881 and 2021. In the ranking of the hottest summers in Germany since measurements began, six summers from this millennium are represented. The four warmest years since 1881 are 2018, 2020, 2014 and 2019.
The fact that it has gotten warmer in Germany, sometimes significantly warmer, cannot be denied. But is this really due to climate change? Yes, researchers say. Heat waves are considered to be the form of extreme weather where the influence of climate change is particularly easy to prove. In storms or devastating floods like last year in the Ahr Valley, it is often more difficult to provide evidence.
The explanation is simple: If the average temperature rises due to man-made climate change, then the temperatures that are possible on a summer’s day in Germany also rise. Cooler days are becoming less likely, scorching heat more likely. A heat wave that would have occurred about once every 50 years before the industrial age now occurs almost five times in 50 years and is on average 1.2 degrees warmer, according to the IPCC’s so-called “sixth assessment report” from this spring. The publications of the Intergovernmental Panel on Climate Change represent the most comprehensive and internationally recognized state of the art in climate research. Hundreds of scientists from all over the world are involved in them.
The influence of climate change on individual extreme weather events can also be tracked. This is where attribution research comes into play. Simulations can be used to calculate whether and how, for example, a heat wave has become more frequent or more intense as a result of climate change.
Attribution research was first used during the great heat wave of 2003, when an estimated 70,000 people died in western Europe. To do this, researchers take current climate models and run them through the computer to simulate thousands of years of weather in the current climate. Then they carry out a second simulation in which they subtract out the man-made emissions of greenhouse gases and aerosols, i.e. they virtually ignore climate change. This is relatively easy to do because the amount of these emissions is known.
The result: A brutal heat wave like in 2003 is rather unlikely even under the current climatic conditions – but without man-made climate change it would be almost impossible. There were similar studies on the heat waves in Europe in 2019, in North America in 2021 or in Siberia in 2020, always with the same result: Without man-made climate change, these violent temperatures would have been almost impossible. “It is extremely unlikely that some past extreme events would have occurred if human influence on the climate system did not exist,” says the Intergovernmental Panel on Climate Change.
Whether humans favor the development of heat waves or not is an important question. Because compared to floods or storms, extreme heat events are a silent killer – and that’s exactly why they are underestimated. In the summers from 2018 to 2020 alone, more than 19,000 people died from the heat in Germany, according to an evaluation by the Federal Environment Agency, the Robert Koch Institute and the German Weather Service in the “Deutsches Ärzteblatt”.
For decades, studies have shown time and again that heat waves put a strain on the respiratory and circulatory systems, that they worsen existing pre-existing conditions and can lead to complications during childbirth in pregnant women. The evaluation concludes that Germany must therefore learn to deal with the heat. And do everything to minimize the number of future heat waves.