Extreme Wetterlagen häufen sich: Bedeutender Klimawert fast überschritten

Von: Lisa Klein, Merkur 

Extreme Wetterlagen gibt es aufgrund der Erderwärmung immer häufiger – auch in Deutschland. Der Klimawandel scheint schneller voranzuschreiten als angenommen.

Der Klimawandel ist weltweit, aber auch in Deutschland immer deutlicher spürbar. Das Wetter verändert sich, die extremen Wetterlagen nehmen zu: Hitzewellen, Dürre, Starkregen, Überschwemmungen, schwere Stürme und enorme Schneemassen sind alles Folgen des Klimawandels. Experten warnen in Deutschland aktuell vor extremer Trockenheit, wie echo24.de bereits berichtete. Während vor einigen Jahren Extremwetter oftmals nicht in direkten Zusammenhang mit dem Klimawandel gebracht wurde, sieht es heute ganz anders aus. 

Wissenschaftler sind inzwischen überzeugt: Extreme Wetterlagen und der Klimawandel hängen zusammen. Die menschengemachte Erderwärmung verändert das Klima unserer Erde – und sie scheint schneller voranzuschreiten als angenommen. Die globale Durchschnittstemperatur eines Jahres könnte laut Weltwetterorganisation (WMO) bis 2026 erstmals mehr als 1,5 Grad über dem vorindustriellen Niveau liegen.

Extrem-Wetter in Deutschland nehmen zu: Erderwärmung schreitet voran

„Wenn die Durchschnittstemperatur steigt, nehmen auch die Extremwetter-Ereignisse zu, und es gibt mehr Hitzewellen. Wir wissen auch: Eine wärmere Atmosphäre enthält mehr Wasserdampf, weshalb stärkere Regenfälle zu erwarten sind“, erklärte Wissenschaftskommunikatorin Susan Joy Hassol bereits 2017 in einem Interview mit klimafakten.de. Beobachtungen von extremen Wetterlagen häufen sich. Die Wetter-Bilanz für 2021 ist schockierend.

Europe lashed by extreme weather as climate crisis grows

PARIS, France – Europe endured record extreme weather in 2021, from the hottest day and the warmest summer to deadly wildfires and flooding, the European Union’s climate monitoring service reported Friday.

While Earth’s surface was nearly 1.2 degrees Celsius warmer than pre-industrial levels last year, Europe saw an average increase of more than two degrees, a threshold beyond which dangerous extreme weather events become more likely and intense, the Copernicus Climate Change Service (C3S) said.

The warmest summer on record featured a heatwave along the Mediterranean rim lasting weeks and the hottest day ever registered in Europe, a blistering 48.8C (120 degrees Fahrenheit) in Italy’s Sicily.

In Greece, high temperatures fuelled deadly wildfires described by the prime minister as the country’s “greatest ecological disaster in decades”.

Forests and homes across more than 8,000 square kilometres (3,000 square miles) were burned to the ground.

A slow-moving, low-pressure system over Germany, meanwhile, broke the record in mid-July for the most rain dumped in a single day.

The downpour was nourished by another unprecedented weather extreme, surface water temperatures over part of the Baltic Sea more than 5C above average.

Flooding in Germany and Belgium caused by the heavy rain — made far more likely by climate change, according to peer-reviewed studies — killed scores and caused billions of euros in damage.

As the climate continues to warm, flooding on this scale will become more frequent, the EU climate monitor has warned.

“2021 was a year of extremes including the hottest summer in Europe, heatwaves in the Mediterranean, flooding and wind droughts in western Europe,” C3S director Carlo Buontempo said in a statement.

“This shows that the understanding of weather and climate extremes is becoming increasingly relevant for key sectors of society.”

– ‘Running out of time’ –

The annual report, in its fifth edition, also detailed weather extremes in the Arctic, which has warmed 3C above the 19th-century benchmark — nearly three times the global average.

Carbon emissions from Arctic wildfires, mostly in eastern Siberia, topped 16 million tonnes of CO2, roughly equivalent to the total annual carbon pollution of Bolivia.

Greenland’s ice sheet — which along with the West Antarctic ice sheet has become the main driver of sea level rise — shed some 400 billion tonnes in mass in 2021.

The pace at which the world’s ice sheets are disintegrating has accelerated more than three-fold in the last 30 years.

“Scientific experts like the IPCC have warned us we are running out of time to limit global warming to 1.5C,” said Mauro Facchini, head of Earth observation at the European Commission’s Directorate-General for Defence Industry and Space, referring to the UN’s science advisory panel.

“This report stresses the urgent necessity to act as climate-related extreme events are already occurring.”

Study Links Heat Waves in Asia to Climate Change

The report, published in the Bulletin of the American Meteorological Society, investigates the causes of a wide variety of extreme weather and climate events from around the world in 2013. Titled "Explaining Extreme Events of 2013 from a Climate Perspective" the 84-page document examines the causes of 16 individual extreme events - including heat waves, rain, flood, droughts and storms - that occurred on four continents in 2013. 

Thirteen independent studies mentioned in the report - compiled by 92 scientists from around the globe – determined there was a link between extreme weather and the burning of fossil fuels. But while the authors found that human influence had substantially increased both the likelihood and severity of heat waves in places like Asia and Australia, it was more difficult to measure the influence of human activity on other events like droughts, heavy rain and storms.

Thomas Peterson, principal scientist at NOAA's National Climactic Data Center and one of the report's lead editors, says in an interview with  Deutsche Welle TV Berlin, that while scientists could not identify a linkage between human-caused global warming and some extreme weather events, the data gathered provides evidence that human activity has increased the intensity and likelihood of heat waves in Asian countries such as China, Japan and Korea.

Peterson: 'Human activity has influenced the strength of extreme weather or increased its likelihood'

Which extreme weather events did you focus on in Asia and why?

Thomas Peterson: Each of the four topics evaluated in Asia was selected by the author team for subjective reasons. Often because the event was of interest to them on a personal level, as it impacted them, their families and their friends. For instance, the report focuses on Japan, Korea and China which all experienced extremely hot summers in 2013.

The fourth topic focused on heavy rain in India. With an early arrival of monsoon-like atmospheric circulation in June, the heavy precipitation that occurred in northern India was a once-in-a-century event.

What were the key findings of the report?

The report found that long duration heat waves during the summer and prevailing warmth for annual conditions are becoming increasingly likely due to a warming planet, as much as 10 times more likely due to the current cumulative effects of human-induced climate change, as found for the Korean heat wave of summer 2013.

Extreme precipitation events of last year were found to have been much less influenced by human-induced climate change than extreme temperature events. Furthermore, prolonged cold waves have become much less likely, such that the severely cold 2013 winter over the United Kingdom was perhaps the most remarkable event of all those studied in 2013 - its probability of occurrence may have fallen 30-fold due to global warming alone.

However, there was no clear evidence of human influence on any of the three very intense storms examined, which included a surprising winter-like storm during autumn in the Pyrenees, an extreme blizzard across the US High Plains, and Cyclone 'Christian' that delivered damaging winds across northern Germany and southern Denmark.

To which extent did climate role play a role in extreme weather events in Asia last year?

All four events evaluated in Asia were found to indicate that human activity had influenced the strength of extreme weather or increased its likelihood. For instance, analyses of observed and simulated June precipitation provided evidence that human-caused climate change has increased the likelihood of much stronger precipitation in northern India, and made heat waves more likely to occur in Japan, Korea and Easter China.

How come human factors were found to have influenced some weather events, but not others? 

Natural variability was a prime cause of all events, just the randomness of the weather. For some of these events, in addition to the natural causes, human influence helped make the events stronger or more likely. But for some events in other regions, the analyses that scientists conducted could not identify a linkage. For a few events, greenhouse gases actually made the extreme event less likely.

Three independent studies which examined Pacific Sea surface temperatures and atmospheric anomalies, found some, but not conclusive, evidence for the impact of human-caused climate change on the ongoing rainfall deficit in the US state of California. For example, one paper found evidence that atmospheric pressure patterns related to the drought increased due to human causes, but their exact influence on the California drought remains uncertain.

So, in your view, which weather events are more likely to be influenced by human factors than others?

Three papers with different methodologies looking at the Chinese, Korean and Japanese heat waves reached the same conclusion. This is a very powerful message. If increases in greenhouse gases are making an event more likely, then it implies that we should expect events like that more often in the future.

The study examined the causes of 16 individual extreme weather events around the world in 2013.

If some extreme weather events could be linked directly to climate change, what does this tell us about the urgency to tackle the issue?

It tells us that climate change is not just in the future but, for example, for the people in eastern China, Korea and Japan, climate change is in their own backyards.

Thomas C. Peterson is President of World Meteorological Organization's Commission for Climatology and the Principal Scientist at the National Climatic Data Center of the National Oceanic and Atmospheric Administration (NOAA) in the United States.

(C) 2014 Deutsche Welle TV Berlin/Germany