Now a new study reveals how these blazes can create a vicious cycle, contributing to climate change even as climate-fueled conditions make for worse wildfire seasons.  Emissions from 2023’s Canadian wildfires reached 647 million metric tons of carbon, according to the study published today in Nature. If the fires were a country, they’d rank as the fourth-highest emitter, following only China, the US, and India. The sky-high emissions from the fires reveals how human activities are pushing natural ecosystems to a place that’s making things tougher for our climate efforts.

“The fact that this was happening over large parts of Canada and went on all summer was really a crazy thing to see,” says Brendan Byrne, a scientist at the NASA Jet Propulsion Laboratory and the lead author of the study.

Digging back into the climate record makes it clear how last year’s conditions contributed to an unusually brutal fire season, Byrne says; 2023 was especially warm and especially dry, both of which allow fires to spread more quickly and burn more intensely.

A few regions were especially notable in the blazes, like parts of Quebec, a typically wet area in the east of Canada that saw half the normal precipitation. These fires were the ones generating smoke that floated down the east coast of the US. But overall, what was so significant about the 2023 fire season was just how widespread the fire-promoting conditions were, Byrne says.

While climate change doesn’t directly spark any one fire, researchers have traced hot, dry conditions that worsen fires to the effects of human-caused climate change. The extreme fire conditions in eastern Canada were over twice as likely because of climate change, according to a 2023 analysis by World Weather Attribution.

And in turn, the fires are releasing massive amounts of greenhouse gases into the atmosphere. By combining satellite images of the burned areas with measurements of some of the gases emitted, Byrne and his team were able to tally up the total carbon released into the atmosphere with more accuracy than estimates that rely on the images alone, he says.