Extreme June heatwave 'much more likely' caused by human-made climate change, says Environment Canada

Last month’s record-breaking heat wave across Ontario, Quebec, and Atlantic Canada was “much more likely” caused by human-made climate change, according to new ground-breaking analysis from Environment and Climate Change Canada.

The June 17-20 heat wave was marked by abnormally high daytime temperatures and warmer-than-normal nighttime lows, according to the agency.

In New Brunswick, all-time maximum temperature records were set in Saint John (34.5 C on June 20) and Bathurst (37.6 C on June 19). Humidex levels across the Maritimes surpassed the 40 C range.

Environment and Climate Change Canada said climate change made the heat wave “two to 10 times more likely to have occurred.”

The June heatwave is the first test of the agency’s “rapid application tool,” comparing pre-industrial climate data with present-day information, then determining human-made climate change effects on a seven-step ranking.

“The system makes use of global climate models and computer simulations of the global climate systems,” said Greg Flato, a senior research scientist with Environment and Climate Change Canada, on Tuesday. “We use those computer simulations of the climate of the 1800s, the period before human activities had caused major changes in the climate, and compare that to simulated data of the current day, when climate has been influenced by changing greenhouse gases, land use, and other activities.

“By comparing those two sets of simulations we can ask the question for a specific event, like the one we’re talking about today, how much has the risk, the probability, the likelihood of such an event been changed by human made climate change.”

Environment and Climate Change Canada said the current heat wave in Western Canada would be analyzed next by the new system, with information expected in a matter of weeks.