647 megatons of CO2 were released by Canada’s wildfires, more than that country’s total emissions.

The wildfires that swept through Canada’s forests last year released more greenhouse gases than any other major emitter, a study found Wednesday, calling into question a national budget that relies on forests as carbon stores.

At 647 megatonnes, carbon emissions from last year’s wildfires exceeded those of seven of the world’s 10 largest emitters by 2022, including Germany, Japan and Russia, according to a study published in the journal Nature.

Only China, India and the United States emitted more carbon dioxide during that time, which means that if Canada’s wildfires were counted among countries, it would be the fourth largest in the world.

Average emissions from forest fires in Canada over the past decade have ranged from 29 to 121 megatonnes. But climate change, driven by the burning of fossil fuels, is leading to drier and hotter conditions, causing more extreme wildfires. The 2023 fires burned 15 million hectares (37 million acres) across Canada, or about 4% of its forests.

The findings add to concerns about relying on the world’s forests to act as sinks for long-term carbon emissions from industries that could instead fuel the problem as they burn.

The concern is that the global carbon budget, or the estimated amount of greenhouse gases the world can continue to emit while warming reaches 1.5 degrees Celsius (2.7 degrees Fahrenheit) above pre-industrial levels, is based on inaccurate calculations.

“If our goal is to really limit the amount of carbon dioxide in the atmosphere, we need to adjust how much carbon we are allowed to emit through our economy, which corresponds to how much carbon is absorbed or not absorbed by forests,” said study author Brendan Byrne, an atmospheric scientist at NASA’s Jet Propulsion Laboratory.

Warmer temperatures in Canada by 2023 are expected to be typical of the 2050s, the study says. This could lead to severe fires across the 347 million hectares (857 million acres) of forests that Canada relies on to store carbon.

Wildfires that spread and the carbon they emit are not counted in Canada’s annual greenhouse gas emissions list.

Carbon is accounted for when it is emitted from human sources, such as industrial activities, and not natural disturbances in forests such as insect outbreaks or wildfires, according to the country’s 2021 National Limitation Contribution Strategy.

“The atmosphere sees this carbon increase, no matter how we set up our accounting system,” Byrne said.

—Gloria Dickie, Reuters