Extract from ABC News
Just six days in to the northern hemisphere summer of 2023, the skyline in New York City was stained in a sepia smoke haze.
It was streaming from across the border, where, what became Canada's most widespread fires in history, were raging.
And the fires did not let up for months.
According to the latest public records, the Canadian wildfires of 2023 have razed 18.5 million hectares of land to date — nearly triple the previous record.
But the months of smoke billowing through the vast boreal forests also did something else.
They released huge quantities of carbon stored in trees and soils into the atmosphere, which some researchers now estimate to be equivalent to 2.4 billion tonnes of carbon dioxide.
To put that into perspective, it's three and a half times the annual emissions for all of Canada's economy, says senior research scientist Werner Kurz who, up until his recent retirement, led the National Forest Carbon Accounting System for Canada.
"2023 was basically a year that was so far off the scale in terms of the [Canada fire] emissions, that we will have to completely revise the way we draw our graphs because the y-axis has to basically be doubled in scale," he says.
"People always talk about unprecedented events, well these were truly unprecedented events."
The estimates are still preliminary with an error of roughly "plus or minus 20 per cent", according to Dr Kurz. But similar figures, between 1.76 and 2.9 gigatonnes, have also been reported by the 2023 Global Carbon Budget and European Union observation agency Copernicus.
Researchers say the numbers are "remarkably high" not just on a local scale, but globally.
It's at least triple the estimated emissions from Australia's Black Summer Bushfires and equivalent to 6 per cent of the projected total carbon emissions for the world this year.
And they were far from the only significant fires. Severe wildfires also consumed swathes of forest and grasslands across Russia, Europe and the United States.
Experts have found climate change made the extreme fire weather experienced in eastern Canada twice as likely during this period.
But with that much CO2 pumped into the atmosphere, have these megafires contributed to climate change themselves?
Fires spark change in global carbon budget
The extreme nature of the northern hemisphere fire season of 2023 prompted an international group of leading scientists to make a change to their annual Global Carbon Budget for last year — considered to be the most comprehensive report of its kind.
For the first time, the carbon dioxide emissions from wildfires were presented in the budget breakdown.
According to estimates, approximately 7 to 8 billion tonnes of carbon dioxide was emitted, overall, from wildfires between January and October 2023.
Pep Canadell, CSIRO's chief research scientist and the executive director of the Global Carbon Project, says the higher-than-normal emissions came despite a less active fire season in the tropics and Africa.
"That was a big deal, and we know that we had to bring that number in," he says.
When it comes to the impact on the climate, Dr Canadell says these fire emissions — though significant — are barely a blip on the radar compared with the decades of accumulated emissions caused by the fossil fuel industry.
They do, however, form part of a broader change in the fire scale and prevalence that has climate scientists worried.
He says off the back of the megafires in Australia, California and Siberia over the last four years, there is legitimate concern that the world is at the precipice of a significant positive feedback cycle that will further add to the already sky-high CO2 emissions.
"This thing is just happening now," he says.
"We don't seem to have had a real impact in the observed global mean surface temperature change we report, yet.
"But if this continues into the future, which we expect it will continue and worsen, then there'll be a real contribution to the growth in atmospheric CO2."
Throwing out the balance
Historically, nature has been good at balancing the books on its fire emissions.
Dr Canadell says that over multi-decade timescales, the carbon absorbed in regrowth tends to balance out what was emitted during the fire.
He points to the regrowth of Australian forests following the Black Summer bushfires as a good example.
"So we ran a study to look at the biomass recovery of the whole forested east, all the way down to the south, and 80 per cent of the areas that burned had almost recovered to the level they had pre-fire in two years," he says.
"That's quite exceptional."
The regrowth isn't the only way nature has been shown to correct the record on fire emissions.
In 2020, researchers found the iron-rich bushfire ash that was transported around the globe during the bushfires triggered an algal bloom the size of Australia in the Southern Ocean.
These algal blooms were so extensive that they may have temporarily offset a substantial amount of the fires' CO2 emissions, according to co-author of the study Richard Matear, an oceans and climate scientist with the CSIRO.
But that carefully balanced cycle of fires to regrowth is starting to be thrown out of whack, according to Dr Canadell.
"Over the last five to seven years, in some regions of the world, we begin to see a new fire regime," he says.
"What was a natural fire, regrow, fire, regrow pattern, is now beginning to see much more fire and therefore less time for regrowing.
"And that's when potential excess CO2 can remain in the atmosphere … and that, of course, will ultimately lead to more climate change."
With increases in extreme fire weather one of the clear consequences of climate change around the globe, Dr Canadell says this is likely to continue.
In Australia, the frequency of megafire years — where more than 1 million hectares burn — has "markedly increased" since 2000, according to a paper published in Nature in 2021.
Burning the carbon sinks
Compounding the problem is not only how much is burning, but what is burning, says Dr Canadell.
While grasslands replace themselves almost immediately, and temperate forests relatively quickly, Dr Canadell says the peatland and boreal forests can take centuries to regrow — if at all.
"That's why the hotspots of Canada and Siberia are very important," Dr Canadell says.
"Because there's a huge imbalance between the old emissions going up very quickly, and an extremely slow regrowth, taking many, many decades to hundreds of years."
That is why Dr Kurz says the Canadian fires this year are particularly devastating.
"These forests can be 50 to 250 years old," he says.
"It gets even more serious when you consider the consumption of forest floor and soil carbon because those are often even older than the biomass carbon."
He says the direct emission estimates from this year may only scratch the surface.
"This wood that was just killed will start to decompose, and we'll add further emissions to the atmosphere," he says.
Shorter term impacts
Not all bushfire impacts on the climate are long-lasting, nor do they always produce warming.
"In subsequent years, there other factors that contribute to warming such as the soot and the black carbon that is spewed out by fires on snow surfaces in Greenland, Antarctica and the Arctic," Dr Kurz said.
"And then there also can be negative feedbacks from air pollutants that are added to the atmosphere that can contribute to cooling."
One research paper into Australia's 2019-20 bushfire found the copious amount of smoke had a temporary cooling effect across the southern hemisphere, by causing the clouds to become thicker and longer-lasting.
It found this may have also contributed to the onset of the rare triple-dip La Niña.
Studies like this are yet to be done on this year's Canada bushfire, however.
"But the bottom line is, having such huge emissions is another greenhouse gas that is eating away at our carbon budget," Dr Kurz said.
For Dr Kurz and Dr Canadell, it's just another reason for policymakers to heed the warnings about climate change and fossil fuel emissions before it gets to a point where they can't be turned around.
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