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The Fort McMurray fire’s stunning pulse of carbon to the atmosphere

An aerial photo of Highway 63 south of Fort McMurray, Alberta, shows smoke from vast wildfires on May 5, 2016. MCPL VanPutten/Canadian Armed Forces/Handout via Reuters

The Fort McMurray wildfire, which seems likely to be the costliest disaster in Canada’s history, continues to grow. According to the government of Alberta, as of Friday morning it had burned over 500,000 hectares of land, or more than 1.2 million acres.

These are preliminary numbers, to be sure, and shouldn’t be taken as precise. They’re also likely to change. “There will be wet areas, boggy areas that don’t burn. But it’s not out yet, either, so . . . even without any major runs, by the time it is contained, it will likely grow some more,” said Steve Taylor, a research scientist with the Canadian Forest Service.

Taylor said the fire already ranks in the top six or seven largest fires seen in Canada in the satellite era, starting in 1970, when observations became most reliable. Especially since this is occurring in May, early in the wildfire season, that’s pretty incredible.

And so is another detail about this fire — the amount of carbon that it is apparently pouring into the atmosphere.

Taylor’s colleague, Werner Kurz, is a senior research scientist at the Canadian Forest Service and heads its carbon accounting team.  He said he generally estimates that for every hectare of forest land consumed in a fire like this one, about 170 tons of carbon-dioxide-equivalent emissions — so dubbed because they actually include not only carbon dioxide but also methane and nitrous oxide, two other greenhouse gases — head into the atmosphere.

That would mean that this single fire has contributed — for a rough estimate — some 85 million tons of carbon-dioxide-equivalent emissions.

The fire has also, at least temporarily, worsened the entire nation of Canada’s emissions of carbon dioxide.

In 2014, the last year for which statistics are currently available, Canada emitted a net of 732 million tons of carbon dioxide equivalent into the atmosphere. This single wildfire thus may have given off enough carbon to account for over 10 percent of Canada’s total emissions.

“And this is not unusual,” said Kurz. “We had other fire years in Canada where the total emissions, over the entire fire season, certainly approached 20 percent or more of the total emissions. Forty percent, even.”

A little over a week ago, when the fire had consumed just over 200,000 hectares, Kurz estimated, in an interview with the Edmonton Journal, that it was already at 5 percent of Canada’s total emissions.

I asked Guido van der Werf, a fire emissions researcher at Vrije Universiteit Amsterdam who charted the incredible pulses of carbon to the atmosphere due to Indonesian peat fires last year, how much he thought the emissions might be from the Fort McMurray fire. Assuming a million acres burned — a smaller number than the one above — van der Werf came up with 35 million tons  of carbon dioxide equivalents, a similarly smaller figure but also one that’s roughly in the same ballpark.

“The difficulty in calculating emissions from these boreal forest fires is that a large fraction of the emissions are from burning the organic soil. And the deeper the organic layer, the more emissions,” van der Werf said by email.

Indeed, another expert, Mike Flannigan of the University of Alberta, thinks that the 85 million ton estimate might even be a little low — precisely because of the depth of the burn. “It was a deep-burning fire due to the prolonged drought,” Flannigan said by email. He also noted that the fire is continuing to grow. Indeed, it just crossed the border into Saskatchewan.

Granted, for emissions, the fire is nothing like the fires in Indonesia last year. Those contributed over a billion tons of carbon-dioxide-equivalent emissions to the atmosphere, according to van der Werf’s calculations, because they burned into deep stores of carbon-rich peat.

Anyway you look at it, though, in addition to all of the other devastating consequences of this fire, there’s a major carbon pulse into the air.

Granted, there’s some good news here, at least for this particular landscape: Trees grow back again, over time, and pull that carbon back in. “Within 10 to 20 years, that net balance is zero,” says Kurz. “And from that point on, the regrowing carbon removes more from the atmosphere than is decomposing, and you get a carbon sink again.”

However, the burning of northern forests can also leave behind a dark upper surface layer that absorbs sunlight, heats up and then thaws permafrost, or frozen soil, beneath the surface. Fort McMurray is located in a zone of Canada that’s still far enough south to see only “isolated patches” of permafrost beneath the ground — but if any of that thaws in the wake of this fire, it will emit carbon into the atmosphere. And that might not get put back in the ground again, at least not on any time frame relevant to the immediate future.

The threat of megafires to permafrost becomes more and more of an issue as you travel farther north in Canada, Alaska and Siberia, which is why northern wildfires can be such a major problem — especially if they are worsening, as appears to be the case.

It all serves to underscore why, in an age of megafires, we have to worry not only about the damage they can do to human lives and infrastructure, but also how they fit into the broader climate system.

Read more at Energy & Environment:

Why Trump’s idea of ‘renegotiating’ the Paris climate agreement is so bizarre

As tree killing disease ravages California, scientists urge the public and leaders not to give up

Even for the fast melting Arctic, 2016 is in ‘uncharted territory’

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