Climate change intensified the weather conditions that fuelled Canada’s most devastating wildfires, according to a new study.

World Weather Attribution, an international team of climate scientists led by Dr Fredi Otto from the Grantham Institute – Climate Change and the Environment at Imperial College London, found that climate change made the hot, dry and windy conditions that drove the wildfires in Quebec, Canada this year at least twice as likely and 20-50% more intense.

The 2023 wildfire season has been the most devastating ever recorded in Canada.

To date, more than 15 million hectares have already burned – an area larger than Greece or New York State – nearly doubling the previous 1989 record of 7.6 million hectares.

Almost 200,000 people have been evacuated from impacted areas so far – the highest number of wildfire evacuees since at least 1980.

“The word ‘unprecedented’ doesn’t do justice to the severity of the wildfires in Canada this year,” explains Dr Yan Boulanger, a Research Scientist at Natural Resources Canada and one of the authors of the study.

“From a scientific perspective, the doubling of the previous burned area record is shocking.”

Wildfire is a naturally occurring phenomenon in Canada, with many wildfires ignited from lightning, but Dr Boulanger says that hotter temperatures are drying vegetation, increasing the likelihood of wildfires both starting and spreading.

“Climate change is greatly increasing the flammability of the fuel available for wildfires – this means that a single spark, regardless of its source, can rapidly turn into a blazing inferno.”

Studying fire weather

World Weather Attribution studies commonly use one weather variable to study an extreme weather event. For example, temperature is used to study heatwaves and rainfall is used to study flooding.

However, because several weather variables influence the conditions that set the scene for wildfires to burn, the researchers decided to study the Fire Weather Index (FWI).

The FWI combines temperature, windspeed, humidity and precipitation to reflect the risk of wildfire taking hold and spreading if an ignition occurs.

Using the FWI, the researchers calculated the cumulative Daily Severity Rating – which reflects the accumulated intensity of weather conditions conducive to wildfire - from the start of the fire season  to the end of July, and found that climate change made the fire-prone weather conditions at least seven times as likely and 50% more intense.

The researchers also analysed the 7-day maximum of the FWI to assess the peak intensity of the fire weather, concluding that such extreme values were twice as likely to occur and around 20% more intense because of climate change.

Dr Clair Barnes, a Research Associate in the Grantham Institute at Imperial College London and the lead author of the study, says there is a small, but growing body of evidence linking climate change with increased fire weather.

“While the role of climate change in other extreme weather events has been well evidenced by attribution science, the unique characteristics of fire weather in different regions of the world means wildfires are more complicated to study.

“However, from the limited number of studies available, it's becoming evident that the dry and warm conditions conducive to wildfires are becoming more common and more intense around the world as a result of climate change.”

The warm and dry conditions are also leading to longer wildfire seasons.

Philippe Gachon, Professor at Université du Québec à Montréal and a contributing author, says that in many regions of Canada, snow plays a key role in determining both the start and length of the wildfire season.

“This year, high temperatures led to the rapid thawing and disappearance of snow during May, particularly in eastern Quebec, resulting in unusually early wildfires.

“The ongoing loss of snow in a warming climate means that wildfires will burn for many more days each year in Canada.”

Bad air

The impacts of the wildfires were far-reaching.

In early June, plumes of smoke from the Quebec fires drifted into the northeastern United States.

The dangerously poor air quality led to sharp increases in asthma-related emergency department visits and school closures.

On the evening of 6 June, with skies coloured a hazey orange, New York City had the worst air quality of any city in the world and by 7 June, more than 120 million Americans were affected by air quality alerts.

According to the study, the people most vulnerable to the toxic wildfire smoke were those with underlying health conditions, reduced access to health services and living in low quality housing.  

With weather conditions that fuel wildfires intensifying due to climate change, the researchers say it is critical to raise public awareness of the health risks posed by dangerous air quality from wildfire smoke.

“Increasing temperatures are creating tinderbox-like conditions in forests in Canada and around the world,” says Dr Fredi Otto, co-founder of World Weather Attribution.

“Until we stop burning fossil fuels, the number of wildfires will continue to increase, burning larger areas for longer periods of time.”