Did climate change cause Canada’s wildfires?

Isabella Kaminski digs into the science on the role climate change and other factors play in wildfires. A spate of serious wildfires across Canada have become a global story in recent weeks, accompanied by photos of murky orange-hued landscapes.

The fires have worsened air quality across the country and down into the neighbouring US, and required tens of thousands of people to be evacuated. With more than four million hectares (10 million acres) already burned it is now on track to be the country’s worst wildfire season ever.

Some Canadian politicians were quick to connect the disaster with global warming. On Twitter, prime minister Justin Trudeau wrote that “more and more of these fires” were being seen because of climate change. Canada’s environment and climate minister tweeted that they “remind us that carbon pollution carries a cost on our society, as it accelerates climate change”. However, Ontario premier Doug Ford, who has tried to roll back a number of climate policies, declined to make the link.

There is a clear connection between climate change and the number and severity of wildfires worldwide. Attributing a particular fire or spate of fires to climate change, however, is more difficult.

The latest report from scientists at the Intergovernmental Panel on Climate Change (IPCC) in 2021 found that fire weather – dry, hot, windy conditions that make it more likely for fires to take hold – is already a growing problem in many parts of the world and will become more common in some regions if climate change gets worse.

“We know that human-induced climate change is warming Canada at about twice the global average rate,” says Nathan Gillett, a research scientist at the Canadian government’s environment department. A 2018 study by Canadian scientists found a significant rise in the number of large fires and area burned across Canada since 1959, with the fire season starting approximately one week earlier and ending one week later.

But can we link a specific wildfire, or spate of wildfires, with climate change directly?

Historical datasets and complex statistical models have made it possible for researchers to show the impact of rising greenhouse gas emissions on heatwaves around the world, for example, by making them more likely or severe.

Wildfires, however, result from a complex interaction of factors, involving short-term weather and longer term climate patterns, the type of forests involved and what people are doing to them. And they all need something to spark them off.

Kira Hoffman, a researcher specialising in fire ecology at the University of British Columbia and the Bulkley Valley Research Centre, stresses that fire is a natural and common part of the ecosystem in western Canada, which is drier and more prone to lightning strikes.

On the other hand, British Columbia’s fire season was so bad in 2017 that it broke its own records for the area of land burned. A study later found that climate change had a “profound influence”, greatly increasing the chance of underlying extreme warm and dry conditions and increasing the area burned by a factor of seven to 11.

This year’s fire season is unique in not being isolated to a particular province, says Carly Phillips, a research scientist at the Union of Concerned Scientists in the US. What links the provinces is hotter than usual temperatures for this time of year and a prolonged period of drought, both of which raise wildfire risk and are getting worse in some places due to climate change.

“Canada has incredibly diverse ecosystems,” says Hoffman. “And what we’re seeing is drought in the prairies, in the mountainous ecosystems, in the Maritimes [provinces]. So places that maybe wouldn’t have as much fire activity on a normal year, like Nova Scotia and Halifax, are now seeing many more ignitions.”

Lynn Johnston, a forest fire research specialist with Natural Resources Canada, adds that the fire season started a lot earlier than usual this year in some places.

Researchers at World Weather Attribution, who explore the connections between extreme weather and climate change, will be analysing the current Canadian wildfires but say they need to update their methodology for fires first.

Although the genesis and spread of a wildfire is “complicated”, however, Johnston says she is less hesitant than she used to be about making the link to climate change. Hoffman is also concerned when media reports on wildfires do not make the link to climate-induced disasters. “The science is very much telling a different story.”

Nevertheless, they all acknowledge there are other important factors at play.

Human development into forested areas increases the risk of people or their infrastructure sparking fires, says Phillips.

Researchers have also long drawn attention to the way that Canadian forestry policies moved away from traditional and Indigenous practices of planned burning which safeguard valuable timber resources and people. Regular, controlled burning clears the forest understory and reduces the risk of larger fires spinning out of control, but this had been stopped in much of the country.

There has been a change of mindset in recent years, with forestry researchers and managers increasingly recognising that fire suppression is “not always necessary or desirable”. Fires are more frequently left to burn in places where they do not immediately affect peoples’ lives or property, and there has been a return to planned burning in some provinces.

However, the legacy of suppression, as well as the planting of more commercial but less fire-tolerant tree species, has made it easier for fires to spread. A recent IPCC summary report identifies “fire suppression in naturally fire-adapted ecosystems” as one of the ways in which people are adapting poorly to climate change.

Fire is coming, and it’s going to get worse. We need to be better prepared for it – Kira Hoffman

Another potential cause of some of the fires increasingly being raised on social media and in some press reports is arson. One conspiracy theory circulating online even claims some of the fires were sparked by “ecoterrorists” trying to dramatically draw public attention to climate change or to force through a restrictive climate agenda.

While some of these incidents are being investigated by police, researchers say there is no evidence that they are the main cause of the problem. Hoffman notes that roughly half the wildfires across Canada every year are ignited by lightning strikes, although the proportion is usually greater later in the summer. On 1 June, lightning sparked around 200 fires in Quebec overnight.

The other half of wildfires are sparked by human activity. But this is mainly accidental, from incidents such as motor vehicle accidents, off-road vehicle ignitions, fireworks or people not putting out campfires.

“Most of the fires we’re seeing now are caused by lightning and we know that because we have lightning strike density maps,” says Hoffman. “We can see the systems come in, we can see the positive cloud to ground lightning strikes and the ignitions right after. The misinformation [about arson] is really concerning because the science is very clear.”

Johnston adds that the number of lightning strikes appears to be rising, and that could also worsen with climate change.

Hoffman, a former firefighter, says conversations around fire management are already better than they were 20 years ago. But she thinks it vital to understand all the different factors at play in wildfires such as the Canadian ones this year, most of which are ultimately human, to be able to respond properly to them. “Fire is coming, and it’s going to get worse. We need to be better prepared for it.”

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