The rise of “extreme weather attribution”

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Homes crumbled at odd angles into the murky water, surrounded by debris and pipes that hadn’t been underground for a long time. Crumpled cars got stuck on roads that turned into rivers.

These were the scenes in parts of Germany and Belgium last July, after torrential rains caused devastating floods. It left large areas submerged, caused extensive damage and claimed more than 150 lives.

Just days later, images from across the world emerged from waterlogged subway stations in the Chinese city of Zhengzhou, which was hit by record-breaking rainfall.

They were part of a series of extreme weather events in rapid succession in the middle of 2021 and drew attention to growing threats from climate change. Yet politicians, newscasters and scientists have struggled to explain precisely how warming has contributed to disasters.

“The sum of all the events we are witnessing in Germany and the forces with which they are occurring all suggest . . . that this has something to do with climate change,” Angela Merkel, then German Chancellor, said in the aftermath of the floods.

Floods and landslides in western Austria last year caused extensive damage © JFK/EXPA/AFP/Getty

The media explained that a warmer atmosphere could hold more moisture, which would make heavy rainfall more likely, but they did not blame the floods in Europe and China on climate change.

However, a scientist took umbrage with a common phrase used by the BBC, that “linking a single event to global warming is complicated”. The science had “evolved”, said Ed Hawkins, professor of climate science at the University of Reading. “How about ‘experts say that climate change is already increasing the frequency of extreme weather events, and many isolated events have been shown to have been made worse by global warming?” he suggested.

The thirst for knowledge about how climate change influences natural disasters has encouraged the growth of a burgeoning field of study: extreme weather attribution.

That climate change is altering the weather we experience is undisputed: last year, the world’s top climate scientists said in a major United Nations report that ‘unprecedented’ weather events would become more frequent due to global warming .

The challenge is to understand how rising temperatures influence fires, floods or storms. Scientists say this means examining how much of an extreme event was caused by climate change and how much more severe it is.

“The fundamental question at the heart of attribution science is: in the absence of climate change, how would this situation be different?” says Rupert Stuart-Smith, research associate in climate science and law at the University of Oxford.

Map animation showing how the Dixie Wildfire spread.  The fire started in Feather River Canyon near Cresta Dam on July 13 and moved northeast.  By the time it was brought under control, the Dixie Fire had burned nearly 3,900 square miles, making it the second largest blaze in California history.

Identifying cause and effect requires a lot of brains – human and computerized. Researchers run computer simulations of the Earth’s climate system to see how often an event would occur under different scenarios. They could include the world 500 years ago, the world today, and the world in, say, 100 years.

Some models are very “zoomed” and cover relatively small areas. This is useful for understanding forest fires, for example, which are heavily influenced by very local weather patterns. Other models are much more “zoomed”, such as those used to analyze heat waves that affect much larger areas.

Scientists analyze the numbers by looking at how often the extreme event occurred in each modeled scenario and decide whether climate change made it more likely or more severe.

A general view of the northeast flank of the Sugar Fire
California has experienced severe wildfires in recent years; a UN report has warned that extreme weather events will become more frequent due to global warming © Neal Waters/Anadolu Agency/Getty

However, no weather event is caused by climate change alone. Extremes, and the extent of the damage they cause, will be the result of many factors, including local weather conditions, such as recent levels of rainfall, as well as an area’s environment and design. Does a riverside town have flood defences, for example?

Understanding how all of these things come together is crucial for planning. Although heavy rains and the bursting of river banks are unavoidable, communities may have plans in place to help minimize damage.

It is essential that we learn practical lessons from these extremes, says Tim Palmer, Royal Society Research Professor of Climate Physics at Oxford University. “Ultimately, this is going to have to lead to big decisions about how to revamp our infrastructure so that it’s more resilient,” he says.

Last year, NATO Secretary General Jens Stoltenberg also said that climate change had clear implications for international security, and that “many military infrastructures will be directly affected by global warming”. [and] sea ​​level rise”.

As the science of attribution improves, researchers believe it could be used in court cases, to tie polluters more directly to climate change and its effects. “The legal community is increasingly recognizing that evidence like this is highly relevant to prosecutions,” says Stuart-Smith.

Saúl Luciano Lliuya, a Peruvian farmer, is suing German energy company RWE over its alleged role in climate change, and the impact warming is likely to have on the region. Luciano Lliuya wants RWE to help pay for flood defenses to protect his town of Huaraz, threatened by nearby glacial Palcacocha Lake. The current case could have big ramifications. If successful, copycat cases are likely to arise, says Stuart-Smith, so we could see many more.

Teacher Questions

  1. Explain what severe weather attribution is.

  2. How do scientists diagnose whether or not an event is due to climate change?

  3. Examine how climate change is expected to have a significant impact on infrastructure and international security.

  4. Referring to the map, explain why this is an effective method of presenting data to show the spread of a fire.

Alasdair Monteith, Gordonstoun

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