The wildfires that ravaged Canada’s boreal forests in 2023 produced more planet-warming carbon emissions than the burning of fossil fuels in all but three countries, research published on Wednesday has found.

Only China, the United States and India produced more emissions from fossil fuels than the Canadian fires, according to the study, which was published in the journal Nature.

The wildfires last year call into question how much carbon the forests will absorb in the future, scientists said. That, in turn, may make it necessary to reconsider calculations of how much more greenhouse gas humans can add to the atmosphere without pushing temperatures beyond current global targets.

The most ambitious limit set in the 2015 Paris Agreement was 1.5 degrees Celsius, or 2.7 Fahrenheit, above preindustrial times. Beyond that threshold, scientist say, it will be increasingly difficult for humans to adapt to a hotter planet.

The boreal forests have historically helped to slow climate change by storing carbon as trees grow rather than adding carbon dioxide to the atmosphere. While the hot and dry weather that fueled the fires in Canada last year was extraordinary when compared with historical records, climate projections suggest it will become common in the 2050s if the world continues on the current trajectory of global warming.

“This brings up a lot of concerns about whether these fires will happen more frequently,” said Brendan Byrne, a carbon cycle scientist at NASA’s Jet Propulsion Laboratory in Pasadena, Calif., and one of the authors of the study. “That could potentially have a big impact on the ability of these forests to store carbon.”