This article was written by Kate Allen and was published in the Toronto Star on August 29, 2024.
Last year, the top three emitters of heat-trapping carbon pollution were China, the United States and India.
Just missing the podium, in fourth place: that summer’s Canadian wildfires, which released more carbon into the atmosphere than every other country in the world, according to a new study published Wednesday. Wildfire emissions over five months, from May to September of 2023, were more than four times larger than Canada’s annual fossil fuel emissions from all other sources, the researchers calculated.
The study, published in the journal Nature, adds another shocking statistic to a wildfire season that has racked up many.
But it also adds to a growing and critically important area of research on the health of Canada’s forests, which currently siphon off a big chunk of the carbon emissions humans release and prevent the world from warming even faster.
“When we emit carbon, we get this big discount of carbon taken up by the forest. And in a lot of ways we kind of rely on that discount,” said Brendan Byrne, lead author of the new study.
“For that reason, it’s very important to understand how these forests and natural ecosystems are absorbing and releasing carbon.”
Byrne is a scientist at NASA’s Jet Propulsion Laboratory in California. But he was born in Alberta and raised in British Columbia, so when Canada’s forests started burning out of control last summer, he was paying attention.
“Being Canadian, I was watching the fires probably more than I would have otherwise. And that was really what got me interested in this study,” Byrne said.
Other estimates of the carbon emitted by last summer’s Canadian wildfires already exist. But Byrne and his colleagues wanted to try a different method they thought would be more direct and reduce some of the uncertainties. The other estimates follow a “bottom-up” approach: they use satellites to calculate how much ground is burning, and then estimate how much carbon had been stored in those areas.
Byrne and his colleagues flipped this, using a “top-down” approach. When forest fires burn, they send big plumes of smoke into the air that contain carbon monoxide. Byrne’s team used data from a different satellite that measures the big increases in carbon monoxide as it passes over the plumes. With that data they can back-calculate how much total carbon the fires released.
To ground-truth some of their calculations, they also relied on a structure about the size of a school portable sitting in a forest in northern Saskatchewan. For years, University of Toronto professor Debra Wunch has been recording concentrations of carbon monoxide and carbon dioxide using an instrument sitting inside that structure.
Like Byrne, Wunch was watching the fires closely, and the measurements that were rolling in from her instrument — the highest she had ever recorded.
“It was really intense, and really sustained,” said Wunch. So intense, in fact, that the instrument itself came close to disaster: fires came within a kilometre of the structure itself. “It was a bit touch-and-go there,” she said.
All of this data was used to create an estimate for 2023 Canadian wildfire carbon emissions that surprised even the scientists who had produced it: 647 megatonnes, greater than Japan’s, Germany’s or Russia’s annual emissions and comparable to India’s total of 740 megatonnes.
“It’s hard to get your head around, because it’s so much bigger than any other Canadian season we’ve seen,” said Byrne.
While forests everywhere sequester some of the greenhouse gases humans emit, Canada is particularly important because of how vast our forests are — Canada is home to 8.5 per cent of all globally forested area — and because the country is warming at twice the rate of the rest of the world, Byrne added.
Wednesday’s Nature study and another published in the journal last week both examined the drivers of the unprecedented 2023 fire season, and came up with similar results. Hot and dry weather — the most extreme since 1980 — was the principal driver of fire spread, Byrne and his colleagues found. Human-caused climate change enabled extreme fire weather conditions over a long period, the other recent study found.
Both studies found these conditions were becoming more frequent; Byrne and his colleagues looked at climate projections and found that the extreme temperatures of last summer would be typical during the 2050s.
But how exactly the Canadian wildfire season will evolve — and when we will get another season like last year’s — is hard to predict, said Piyush Jain, the lead author of last week’s Nature study and a scientist with the Canadian Forest Service.
Climate models can help predict future weather conditions, but other elements, like lightning — a common ignition source — are hard to model in fine detail, Jain said. It’s also hard to know how vegetation and tree species might shift with many more active fires.
“There’s still a lot not known. Fire is a complex phenomena,” Jain said.
But overall, studies show, “the probability that any given year in the future will be more extreme is increasing. And so we would tend to see these years more.”
Samantha Green, a family physician with Unity Health Toronto and a volunteer with the Canadian Association of Physicians for the Environment, says that while the carbon emissions numbers might be mind-boggling, action is both possible and necessary.
“It’s upsetting. It’s not surprising,” said Green. “We know that with increasing climate change, we will see these feedback loops happen, unfortunately, and I think it should act as more motivation to stop burning fossil fuels.”
Green notes that in addition to the direct health harms from smoke and fire, wildfires also cause trauma and displacement.
“Sometimes when we see these numbers, it’s just so abstract … and then people feel just so dejected, like there’s nothing that we can do about this — when in fact, what it means is that we need to do everything about this, that every action that we take matters.”
