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In January 2003, physicist  watched as floodwaters from the Thames river threatened to seep into his home in Oxford, UK. He  why meteorologists at the time were refusing to blame climate change for the event.

Later that year, Peter Stott, a climate scientist at the UK’s Met Office, arrived in Italy for a summer holiday. But instead of a week of ice cream and beach reads, Stott found himself trapped in . “For me, that was a really striking experience, because I’d never experienced 40°C heat before,” he says.

Both Allen and Stott wanted to pin down the role of climate change in driving the extreme weather they had experienced. Stott realised existing climate models could be used to run an experiment simulating two model worlds in which the European heatwave occurred: one mirroring the 2003 climate and one without human-caused warming.

Together, Stott and Allen ran the model simulations for both worlds thousands of times and concluded, in , that human activities had at least doubled the risk of the 2003 heatwave striking.

It was the start of a whole new field of climate science, for the first time identifying our influence on a specific extreme weather event. Soon, attribution analysis was being performed on all kinds of extreme events, from heatwaves to severe droughts and rainstorms.

But there was still a hitch. It took months, sometimes years, after an extreme weather event for researchers to produce the analysis to declare the influence of climate change.

A group of researchers, including Friederike Otto at Imperial College London, decided to change that with the launch of World Weather Attribution in 2014. The team performs rapid analysis of extreme weather events to quantify the possible influence of climate change, often getting the results out to the public and media within days of the extreme weather hitting.

The result was a huge shift in how such events around the world are communicated, with contemporary news reports now able to directly blame climate change for deadly weather, driving home the real-world impact of rising emissions.

“When we started doing this 10 years ago, every scientist and every journalist was saying, ‘you can’t attribute an individual weather event to climate change’, and that has dramatically changed,” says Otto.

It has even paved the way for climate lawsuits, with attribution studies acting as evidence in dozens of cases against polluters around the world. It has also opened the door to climate change reparation payments, with a new international loss and damage fund established by the United Nations in 2022.

Writing in 2003, Allen asked: “Will it ever be possible to sue anyone for damaging the climate?” The answer, thanks to the advancement of attribution science, is now a resounding “yes”.