Climate change made record-breaking Eastern Canada heat wave ‘much more likely’

TORONTO — The heat wave that enveloped Eastern Canada last month was made between two to 10 times more likely due to climate change, federal officials said Tuesday, offering a sobering and rapid analysis of the effect of planet-warming emissions on the record-breaking temperatures.

Environment and Climate Change Canada says the results of its rapid analysis into the mid-June heat wave over parts of Ontario, Quebec and Atlantic Canada shows it was “much more likely” due to planet-warming emissions.

The results mark the public debut of Canada’s new rapid extreme weather event attribution pilot program, which officials say can determine whether and to what extent climate change made a specific heat event more likely.

The analysis helps drive home how the gradual human-caused changes to the climate, primarily driven by the burning of fossil fuels, have already upended weather extremes in Canada.

“Climate change is not just something in the vague future, it’s something that we’re experiencing now,” said Greg Flato, director of climate research at ECCC.

While other government offices carry out rapid attribution analyses, Environment and Climate Change Canada is thought to be one of the first in the world to publicly roll out a tool and automatically apply it across the country, with results shared within several days.

The heat wave last month toppled dozens of daily temperature records across Eastern Canada. All-time maximum temperature records were also broken in Bathurst and Saint John, N.B.

The same rapid attribution system behind Tuesday’s results will also be applied to the heat wave over Western Canada, once it relents.

The plan is to also apply the program to cold weather extremes this winter, and precipitation, such as flood-inducing rainfall, by next year. There is also work ongoing to have it rapidly analyze the influence of climate change on wildfire activity.

‘By demonstrating and calculating the increased likelihood that we’re already experiencing for events like this, I hope it provides more compelling information for Canadians to understand what the role of climate change means, how it affects our lives, our environment, and how it will continue to affect us as the climate changes,” Flato said.

Hundreds of attribution studies have been published over the past two decades, largely keeping with the same general premise.

Researchers run climate models under two scenarios, one based on a simulation of a pre-industrial climate and another based on a simulation of the climate we have now. They then compare the results to an observed heat wave to figure out how much it was influenced by human-caused global warming.

The federal pilot program behind Tuesday’s analysis has three escalating colour-coded levels to communicate the influence of climate change on a heat wave, from somewhat more likely (between one to two times) to far more likely (at least 10 times more likely). Last month’s heat wave landed in the middle, “much more likely”, at a factor of two to ten times more likely.

Each level has a range given the degree of uncertainty in the climate model simulations, Flato said.

“If we were to give a single number — it has been made 3.7 times more likely — that number would be misleading because it doesn’t provide you … with any kind of sense that it is uncertain and it will remain uncertain,” he said.

Rapid studies, popularized over the past decade by international research groups, look to inject climate science into the discussion when it’s most relevant.

World Weather Attribution, which is made up of a team of international researchers, has been at the vanguard of that work, collaborating with local scientists, including those with Environment Canada, on dozens of studies over the past decade that have helped standardize research practices.

Shortly after a heat wave relented over Mexico last month, the group released a report suggesting it was made 35 times more likely and about 1.4 degrees hotter due to climate change.

Attribution studies can figure out what might be natural climate variation, rather than just human-caused climate change. A World Weather Attribution study of drought across southern Africa earlier this year found El Niño, a natural climate cycle, was the key driver, not climate change.

The Environment Canada pilot program, for its part, will also indicate when there is no evidence to suggest climate change had an influence on an extreme weather event, or whether it was actually made less likely — such as might be the case with a cold extreme.

The analysis comes on the heels of new results showing June marked the 13th straight month of record-breaking global temperatures. It also marked the 12th straight month where temperatures were 1.5 C warmer than pre-industrial times, according to the results released this month by the European climate agency Copernicus.

The 1.5 C mark is also the warming limit countries agreed to as part of the 2015 Paris climate agreement, though scientists note it won’t be considered crossed until there’s longer-term duration above that threshold, as much as 20 or 30 years.

This report by The Canadian Press was first published July 9, 2024.

Jordan Omstead, The Canadian Press