Extreme temperatures and climate change The dangerous impact of heatwaves

Bonn · Human-induced climate change is increasingly producing extreme temperatures. The new weather normality in summer poses challenges, especially for cities. The French have long since reacted to their summer heat trauma of 2003.

This traffic-regulating arrow was already deformed by the last heat wave because the asphalt began to sweat at more than 60 degrees.

This traffic-regulating arrow was already deformed by the last heat wave because the asphalt began to sweat at more than 60 degrees.

Foto: picture alliance / Frank Rumpenhorst/dpa/Frank Rumpenhorst

When looking for headlines, newspapers often find what they are looking for in the weather. For good reason: virtually everyone wants to know "What will it be like tomorrow?" When a heat wave or a heavy storm is approaching, it would be irresponsible not to warn people in advance.

The polar jet stream over Europe has now once again opened the door to Sahara air. On the Iberian Peninsula, devastating forest fires are raging at 45 degrees. It has been clear for a few days that the Rhineland will now also get a whiff of Andalusia or North Africa. 36 degrees? 41 degrees? In any case, these will be dangerous days for vulnerable residents of Bonn. A temperature of 38 degrees is around 15 degrees above the city's long-term maximum temperature in July.

One year after the flood disaster on the Erft and Ahr rivers, documentaries on all TV channels are now reminding us that more than 180 people lost their lives because there was no warning issued. And heat waves are actually even more deadly. By way of comparison: during the week-long heat wave of 2003, around 7,000 people in Germany died because of heat-induced heart, circulatory and respiratory diseases or dehydration (not drinking enough). Elderly people were particularly affected. But to this day, "heat" is not a standardised diagnosis of death, yet researchers estimate about 80 to 90 percent of all extreme weather-related deaths are caused by heat

A wholesale market became a morgue

In 2003, large areas of Europe were engulfed by high "Michaela" and around 70,000 people died. France suffered particularly, with around 20 000 fatalities. Every evening, the heat death toll was announced - like the Covid 19 death toll years later. A wholesale market in Paris became a morgue. In Switzerland, temperatures of over 40 degrees were recorded for the first time in 2003, and the glaciers groaned. Huge amounts of meltwater poured down into the valley. And on the Swiss landmark, the Matterhorn, the permafrost evaporated, causing rockfalls the size of several houses. At times, the zero degree limit in the Alps was higher than Mont Blanc (4807 m), Europe's highest mountain.

In the 21st century, extreme weather events are becoming more frequent worldwide. But any meteorological phenomenon that causes a lot of deaths or extensive damage is often referred to as the "heat of the century" or the "flood of the century" - without any claim to statistical accuracy. The terms are meant to suggest "very rare"; in fact, the heatwave of 2003 was an event that 19 years ago was supposed to occur statistically only once in 10,000 years. Since 2010, however, hardly a summer has gone by without a heat wave in some corner of Europe.

The new weather normal with increased heat or torrential rain has long been a fact, despite many people still classifying it as an exception to the rule. It is not only ordinary people who have difficulty classifying human-induced climate change as a problem of the here and now and not one their grandchildren and great-grandchildren will face. Politicians and civil servants, too, have not yet accepted the new reality. Hardly anyone wants to look the facts in the eye, not even after catastrophes, which is infuriating the insurance industry.

"With the exception of 34 houses, all houses on the Erft and Ahr rivers may be rebuilt on the same site," recently criticised Jörg Asmussen, Chief Executive of the German Insurance Association (GDV). This means: 8966 out of 9000 destroyed buildings may be rebuilt on the old site. Some partially destroyed houses are protected as existing buildings, others are subject to conditions, such as not being allowed to have a living area on the ground floor. Geographer Thomas Roggenkamp of the University of Bonn says this amounts to "flood dementia". No trace of prevention, no awareness of the need for society to adapt to climate change. This corresponds with the latest ZDF political barometer: 30 percent of the respondents to a survey still believe that extreme heat waves are natural weather whims.

The authorities' continue-as-is approach to granting permits is in stark contrast to a recent warning by Ralph Tiesler, Germany's top population protection official. The president of the Federal Office of Civil Protection and Disaster Assistance in Bonn said, "As a population conservationist, I say that some areas should not be resettled due to climate change and the acute threat of severe weather and flood disasters. This question also arises in coastal areas." Tiesler even thinks climate refugees are possible within Germany. He timed his warning precisely before the federal cabinet discussed its "resilience strategy". How can Germany better protect its people and its community from the consequences of climate change? There is a huge gap. Not only must CO2 emissions be reduced, but also Germany's own vulnerability.

Tropical nights in cities

All measurements from the climate lab and findings from the research lab, however, send the same message: that things could get tough; and that temperatures are heading in the direction of tropical faster than humans can adapt to. Extreme weather is no longer a rare occurrence, like a rare meteorite. It will intensify and become more frequent.

Especially in cities, where urban heat islands are forming due to too much asphalt and concrete. Nights are particularly to be feared, when the sun no longer warms, but concrete and asphalt act like night storage heaters and "tropical nights" seep out of buildings and streets. Concrete, for example, has a thermal conductivity about ten times higher than bricks.

One trend will further exacerbate the situation: People are increasingly drawn to the cities, where it is still ten percent warmer at night than in the surrounding countryside. Three quarters of all German citizens are already city dwellers. According to simulations by the German Weather Service (DWD), the number of hot days above 30 degrees Celsius in Cologne/Bonn could more than double from the current 20 to 42 by 2050.

High summer temperatures have caused excess heat-related mortality in Germany for three consecutive years (2018 to 2020) for the first time since the study period began in 1992, researchers from the Robert Koch Institute, the Federal Environment Agency and the DWD wrote in the "Deutsches Ärzteblatt". In figures: 20 000 heat deaths between 2018 and 2020. The scientists are calling for Germany to significantly improve the way it deals with heat waves.

Researchers at the Leibniz Institute for Spatial Social Research (IRS) already know how to do this and propose three tried-and-tested models for action that could be easily integrated into municipal practice: a municipal climate council (tried and tested in Potsdam), a climate check in urban land use planning (Remscheid) and the establishment of a climate staff unit (Würzburg).

But so far, from the point of view of a city hall, this has no more than "nice-to-have" quality. Climate protection and climate adaptation are not (yet) mandatory municipal tasks. Because the situation is urgent, the municipalities hardly have time to develop and test their own solutions, according to the IRS. "They also lack the human and financial resources for this," says urban researcher Wolfgang Haupt.

France responded to heat wave

The French are already many steps ahead. For example, cities now keep a register of all citizens over the age of 60 who live alone, and every city hall has air conditioned rooms where vulnerable people can stay during the day. If a heat warning is declared for at least three days, the emergency plan "Canicule" (heat wave) kicks in. Social workers then call senior citizens, city halls can impose driving bans to prevent exhaust fumes from heating up the city even more. Studies have shown that if ten percent of sealed surfaces are replaced by plants, the city thermometer drops by three degrees.

Many research studies can be found that describe the next decades. What happens if the two-degree target is missed and too little continues to happen in climate protection? The models have earned a high degree of trust because they have accurately predicted the present in the past. By measuring the earth’s temperature and comparing it with climate change in the past, it becomes clear that the pace of climate change now will overwhelm humankind’s ability to adapt. The temperature is rising 40 times faster than it did after the last cold period, which ended about 11,000 years ago. It took an eternity for it to rise one degree more.

In a study published in the journal PNAS, an international team of researchers reports that for millennia, human populations have mostly lived in a "narrow climate envelope between 11 and 15 degrees mean annual temperature", which also applies to their crops and livestock. "All species have an ecological niche, and despite technological advances, humans are unlikely to be an exception," the researchers write.

If the jet stream begins to lurch, extreme weather threatens.

If the jet stream begins to lurch, extreme weather threatens.

Foto: Nasa

This human temperature niche, they say, will shift more in the next 50 years than at any time since 6000 B.C. "One-third of the world's population is then expected to experience a mean annual temperature of more than 29 degrees Celsius, currently found on only 0.8 per cent of the Earth's land surface and mainly concentrated in the Sahara." But by 2070, he said, 29 per cent of the land surface would be affected.

(Original text: Wolfgang Wiedlich;Translation Jean Lennox)
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