This article was written by Bob Weber and was published in the Toronto Star on July 23, 2023.

As firefighters and other first responders battle an unprecedented summer of fires, floods, tornadoes and heat waves around the country, a group of Canadian scientists are asking why they’re happening in the first place.

“May and June were record hot months in Canada and we’ve got the record wildfire season as well,” said Nathan Gillett of Environment and Climate Change Canada. “Yes, it has been busy.”

Gillett heads the Rapid Extreme Event Attribution Project, a new federal program that uses the growing field of attribution science to promptly establish to what extent — if any — a specific flood in British Columbia or wildfire in Quebec is due to climate change.

“The idea is to be able to make rapid extreme event attribution days or weeks after the extreme events occur,” he said.

Twenty years ago, if you’d asked a scientist if climate change was linked to days of rain or months of desiccating drought, you’d probably get an answer along the lines of “We can’t say for sure but this event is consistent with the modelling.”

But in 2003, a paper was published suggesting science could do better. Myles Allen of Oxford University borrowed a concept from epidemiology. “You can say that smoking increases your risk of lung cancer by a certain amount,” Gillett said. “In the same way, you can say human-induced climate change increased the risk of a certain event by a certain amount.”

Since then, hundreds of attribution papers have been peer-reviewed and published. As well as Canada, governments including the United Kingdom, Australia, the Netherlands, South Korea, Japan and the United States are using attribution science.

Attribution science works by comparing climate models. One set of models will use data drawn from actual records while another, otherwise identical, set will be constructed with the influence of greenhouse gases removed.

Simulations will be run using those two sets and the difference in the results reveals the impact of climate change. It allows scientists to say to what extent the presence of greenhouse gases increased the likelihood of the event in question. “It’s probabilistic,” Gillett said. The process is now established enough, with peer-reviewed protocols and standards, that the calculations can be done quickly.

“Once you’ve got the method in place and it’s validated, you really just have to get the observations from that event and you can provide a result,” said Gillett.

Some events are easier to study than others. Gillett said his group hopes to be able to come to conclusions on heat waves in about a week, but wildfires, which involve more variables, will take longer.

Speed matters, said Clair Barnes, a researcher with the World Weather Attribution group in the U.K., which has studied the role of climate change since 2015 in more than 50 events around the world — including the finding that the heat wave preceding the fire that levelled Lytton, B.C., was made 150 times more likely by climate change. “Our aim is to look at high-impact events that are in the news,” she said.

“There was an appetite in the public and the media for more information about what’s really happening now.”

Attribution science does have its limitations. It can only work where there’s enough historical weather data to build an accurate climate model. That leaves out much of the global south, where some of the worst human impacts are occurring. As well, extremely local events are often beyond its resolving power.

The idea is to be able to make rapid extreme event attribution days or weeks after the extreme events occur. NATHAN GILLETT ENVIRONMENTAND CLIMATE CHANGE CANADA