The year 2021 is already a challenge even for climate researchers who are working on climate-related weather escapades. While a heat bell over the USA drove temperatures close to 50 degrees Celsius and a roller of fire rolled over entire villages, the low pressure area of ​​Bernd in Germany and Belgium caused a flood disaster. Only a short time later, the thermometers around the Mediterranean also showed values ​​above 40 degrees, in many places large areas were on fire. “None of this was entirely surprising,” says Friederike Otto. She is co-founder of the research initiative World Weather Attribution, which compares current data on weather events with their computer models and tries to determine with these simulationshow the event in question would theoretically have happened in a world without climate change. In the case of heat, for example, a clear trend can be seen; Scientists are increasingly registering events that lie outside of what would have been expected without climate change. In the Canadian community of Lytton, the existing record was exceeded by almost five degrees Celsius.

39-year-old Otto has had an exciting year.

All over the world it has stormed, burned or rained.

And to an extent that was startling.

And above all there is the question: Was that us?

“Heat waves like in North America and last year in Siberia would have been almost impossible without climate change,” she says.

The occurrence of the events in British Columbia, for example, was more than 150 times more likely due to global warming, as the researchers calculated.

Rainfalls are now also part of climate change indicators.

The extreme precipitation in the Ahr valley and in neighboring regions with up to 150 liters per square meter within one day has become up to nine times more likely.

Extreme weather events are increasing

According to the World Weather Organization WMO in Geneva, there were an average of 711 weather disasters per year in the 1970s;

in the decade from 2000 to 2009 that number rose to 3,536 - that's almost ten such events per day.

More than two million people have died in extreme weather phenomena in the past 50 years, according to this report.

Two weeks ago, experts from science, society and politics discussed for three days at the Extreme Weather Congress in Hamburg (28.09. - 30.09.2021) which risks exist - for human health, for transport systems and for our energy supply.

Despite all the uncertainties in the details, the climate researchers' models have long been considered reliable. But whether attribution, the ascription of an extreme event to climate change, is even possible and what the quality of the results is, is largely determined by the available observation data. The lack of observational data available to science is still a problem right now. Heat waves and heavy rain can now be classified very reliably. The quality of the information increases the larger the region in which the event takes place.

Even in Europe there are regions for which the data situation is insufficient.

Eastern Europe or Turkey, for example, are pretty much unexplored.

The situation is even poorer for the countries of the global south - the very countries that are expected to be much more affected by extreme weather events.

There are definitely still uncertainties in the models.

The researchers assume that non-linearities in the climate system mean that parts of the system can change abruptly or by leaps and bounds.