- How heat changes our lives and endangers them
Climate change isn't just bringing us record-breaking temperatures, it's also introducing new weather terminology. A heat bubble isn't a pressure point under your toe, but rather it's bringing Germany the hottest days of the year so far. "The term heat bubble describes an area with very hot air masses that break away from the African continent and move towards Europe," explains Frank Böttcher, chairman of the German Meteorological Society and expert on extreme weather.
These heat bubbles are particularly intense when they move over Spain and France towards Germany. The air masses cool down slowly as they move further north.
The current heatwave is part of a series of extremes: For 13 months, from June 2023 to June 2024, Copernicus, the EU's climate change service, reported new global temperature records. The 6th of July 2023 was the world's hottest day on average, with 17.23 degrees. In total, there were five such historical record days in July last year. In regions already affected by severe heat, temperatures reached unbearable levels for weeks.
Climate change is particularly affecting Europe. In Southern Europe, there are increasingly frequent severe wildfires due to the heat. In Germany, the temperature in 2023 was 1.2 degrees above the average of the comparison period 1991 to 2000. The result: "It's not only getting warmer on average, heat extremes are also increasing," says climate scientist Andreas Walter from the German Weather Service (DWD) in Offenbach.
More and more heat days with 30 degrees - or more
The number of heat days, i.e., days with air temperatures of at least 30 degrees, has increased nationwide from about three days a year in the 1950s to an average of ten days a year today, according to the National Climate Report of the DWD. "This particularly affects regions that are already very warm," says Walter - for example, the Upper Rhine Valley, the Rhine-Main region, and the area around Freiburg.
Residents are also increasingly suffering from the unusual temperatures elsewhere. The weather station in Munich (city) recorded 25 heat days with values above 30 degrees in 2023 - five times as many as in the period 1961 and 1990, before climate change really took off. The number of summer days (with more than 25 degrees) has more than doubled in the same period, from 36 to 79.
There has also been a doubling in Munich's metropolitan area in the number of tropical nights, from one to two. While this may seem like a small increase, if the trend continues as predicted by climate models, there could be many more such nights in the future.
The further development depends largely on how we behave. If greenhouse gas emissions remain as high as they are now, the number of hot days in the mentioned regions could increase by ten days by the middle of the century. By the end of the century, there could even be 30 extra days with temperatures above 30 degrees. "That's a whole month more of heat," warns Walter.
Even if greenhouse gas emissions were significantly reduced, the average number of heat days would still increase by around seven days per year by the middle of the century.
Each one of these is a torture for the human body. The reason why heat affects us so much is that our organism only functions within a narrow temperature range: ideally for humans, it's around 37 degrees internally, but just a few degrees above that can alter the structure of many proteins that make up a large part of the body, damaging tissues and metabolic processes. Severe overheating can be life-threatening: the Robert Koch Institute estimated around 3,200 heat-related deaths in Germany for the summer of 2023, with 2,700 being aged 75 or older.
In response, the body literally does everything in its power to keep its temperature in the safe zone. Our thermoregulation center, our 'thermostat,' is located in a small structure in the brain: the hypothalamus. Under its control, sweat glands release fluid that evaporates on the skin, producing coolness. The hypothalamus also regulates our thirst to quickly replace lost water. Additionally, more blood is redirected from the body's interior to the small vessels directly under the skin to dissipate heat through the cooled periphery. That's why we get a beet-red face in the heat.
All these efforts put our organism under pure stress: the heart has to pump faster to maintain blood pressure because much blood is diverted to the vessels under the skin. Sweating causes water and salts to be lost from the circulation, making it hard to sleep on hot nights.
Even for healthy individuals, heat can become a risk. Babies, due to their weight-to-surface ratio, have less skin area for sweating than adults and are thus more prone to overheating. Older people feel less thirsty and sweat less than younger ones, while pregnant women do so more quickly. For all of them, heatwaves are more dangerous.
The situation is even more dramatic for those who are ill. Especially at risk are people with chronic heart or kidney diseases, says Elke Hertig, Professor of Regional Climate Change and Health at the University of Augsburg. "The body tries to cool down and pump more blood into the vessels under the skin, which puts additional strain on the heart. For kidney patients, the fluid loss from sweating is a problem. If not enough is drunk, the kidney becomes stressed as well."
Nighttime heat increases stroke risk
A particular problem is nighttime heat, which robs us of sleep. A German stroke study published in May by some colleagues of Elke Hertig at the Helmholtz Center Munich shows that the sweatiest nights can potentially be life-threatening: the team compared over 11,000 strokes from 2006 to 2020 in the Augsburg region with nighttime climate data. In the hottest 2.5 percent of nights, the risk of strokes increased by seven percent. The link was particularly clear for strokes caused by blood clots, in the elderly, and in women, which could be related to hormonal factors.
Heat-related risks also apply to people with certain rare diseases. In the case of scleroderma, a rheumatic inflammation and hardening of the skin, many sweat glands are often lost due to the disease, making it difficult to cool down. Cystic fibrosis patients sweat out a lot of salt and have a higher risk of slipping into an electrolyte deficiency.
In connection with high heat and strong sunlight, there are a number of typical emergency situations, says Dr. Lüder Warnken, a Hamburg emergency physician: "In a heat stroke, the body cannot release excess heat - for example, because one is not wearing appropriate clothing or the environment is simply too hot." Those who stay too long in direct sunlight without head and neck protection can get a sunstroke with racing headaches and severe nausea.
These are the causes of a heat collapse
"The cause is excessive exposure to heat radiation from sunlight, which irritates the brain membranes," says Warnken. Those who are excessively active at high temperatures and drink too little risk heat exhaustion. A heat collapse, on the other hand, is a circulatory malfunction in which the vessels dilate due to heat, parts of the blood "sink" and are no longer available to the heart, which can lead to a brief loss of consciousness. This can be promoted by alcohol consumption and long periods of standing in large crowds.
The correct reaction to most of these symptoms is the same, advises Warnken: "Into the shade, cool the legs with calf compresses, and if the person is conscious, drink plenty of fluids." If there are strong pains, speech disorders or loss of consciousness, the emergency services should definitely be informed on 112.
Hertig has been researching another problem of hot days for years: ground-level ozone. The aggressive gas forms under sunlight, for example, from nitrogen oxides. Therefore, high temperatures and high ozone values often occur together in summer - a double problem for heart and vascular patients: "Ozone irritates the upper airways, but with prolonged exposure affects the whole body and causes inflammatory reactions, for example in the blood vessels," explains Hertig. "In a study, we were able to prove an increased risk of heart attacks at high ozone values - but not at extremely high ones. On such extreme days, it was probably so hot that people stayed indoors and thus avoided the heat and high ozone concentrations."
On hot days, it is advisable to stay in the shade, reduce physical activity, drink enough, and adjust your diet to light meals with plenty of fruit and vegetables that put little strain on the organism. It is also important to ventilate the apartment, especially in the cool night and morning hours, and to shade it, preferably with external blinds that keep the heat out of the building.
However, not only patients should adapt to heat periods - doctors' practices also need to rethink: In the "AdaptNet" project, the team of Elke Hertig is currently training 20 family and specialist doctors in Nuremberg and has, among other things, created heat checklists. Doctors should already try to make their practice "heat-proof" before the summer, for example by buying fans or blinds in time, planning video consultations or early appointments, for example for heart patients, or storing heat-sensitive medications differently.
Many medications also pose risks in hot weather, with some requiring different dosages: The "Heidelberg Heat Chart", created by the university hospital there, lists, for example, blood pressure-lowering ACE inhibitors that dampen thirst. Many antipsychotics and antidepressants disrupt temperature regulation, the epilepsy drug carbamazepine impairs sweating, and insulin for diabetics works faster in the heat, increasing the risk of hypoglycemia.
Urban planners must also rethink due to the heat
In addition to doctors and nurses, especially in cities, architects, builders, and urban planners must also rethink to protect people from heat:
"Water fountains alone are not enough," says climate scientist Andreas Walter. Instead, cities must consider their own microclimate. Concrete buildings, paved streets, and paved plazas absorb heat during the day and release it into the night air, resulting in tropical nights with temperatures not dropping below 20 degrees. This particularly affects people who are already health-impaired. Only below this temperature threshold can the body recover from hot days.
How cities can prepare is clear in theory: more green spaces, less sealing, and especially corridors that allow cool night air to flow into the heated inner cities. However, more and more people are moving to urban areas, and the demand for housing is barely keeping pace with supply. Previously undeveloped areas are becoming highly sought-after building land.
New construction concepts are needed to counter this. Existing low-rise buildings, such as supermarkets, could be expanded to preserve open spaces. But there's the existing building code, which prescribes a parking space for each residential unit.
A national heat protection strategy presented by Housing Minister Klara Geywitz in 2022 alone is not enough. Metropolises must also protect against impending heavy rainfall events. They demand more financial support for the implementation of their adaptation concepts.
And the truth is: Even the best heat protection strategy is useless if humanity does not significantly reduce greenhouse gas emissions. "With a global warming of four degrees, heat bubbles from Africa could raise temperatures in German cities to 47 degrees," warns Böttcher. Then even German cities face heat collapse.
The term 'heat bubble' describes a phenomenon that has become more common due to climate change, bringing extremely hot air masses from the African continent towards Europe. These heat bubbles are causing record-breaking temperatures, especially in regions like Germany, Spain, and France.
In response to these rising temperatures, the number of heat days with temperatures above 30 degrees has significantly increased in Germany. For instance, Munich recorded 25 such days in 2023, which is five times more than in the period before climate change took off.
