Here’s a NASA image of what the state looked like on June 14, before the bulk of the fire activity began. Notice that some areas show what NASA calls “burn scars” from fires of prior years (they look brownish red):
Now look at what the state looked like as of Sept. 1, after numerous large fires raged in the Alaskan interior:
NASA’s Earth Observatory doesn’t just present these pictures — it also quoted an expert from the University of California Irvine, Sander Veraverbeke, to estimate the consequences of such a burn when it comes to contributing carbon to the atmosphere.
Trees and vegetation remove carbon from the atmosphere through the process of photosynthesis — but burning them releases that stored carbon again. And in Alaskan fires, you aren’t just burning trees, but also a thick layer of mosses and other plant life at the forest floor. That’s what contains the large majority of the carbon, according to Michelle Mack, a forest ecologist at Northern Arizona University.
So what’s the result? NASA quotes Veraverbeke as follows: “a quick back-of-the-envelope calculation is that we are probably looking at emissions somewhere between 37 and 55 teragrams” of carbon. I independently checked with Guido van der Werf, a professor at VU University Amsterdam who studies global fires and their emissions to the atmosphere, and he agreed that “that’s the ballpark number. It’s a pretty big fire year.”
But what does a number like that mean? A teragram is equivalent to a million metric tons. Moreover, because most of that carbon actually gets emitted as carbon dioxide (which has a different mass than carbon), Veraverbeke estimated by e-mail that probably about 118 to 176 million metric tons of carbon dioxide went into the atmosphere this year as a result of Alaska’s fires. Moreover, he explains, there was an additional amount of hard-hitting methane emitted that, if converted to carbon dioxide “equivalents,” ups the total emissions to 128 to 191 million metric tons.
How significant is that? Well, to give one potential point of comparison, the EPA lists annual carbon dioxide equivalent emissions from a large number of U.S. sources, most recently as of 2013. The total in 2013 was 6,673 million (or 6.67 billion) metric tons of carbon dioxide equivalent.
That’s much bigger than any contribution from Alaska’s wildfires, but at the same time, emissions from those fires are larger than, say, emissions from industrial sectors like cement production (36.1 million metric tons) or natural gas systems (36.8 million metric tons).
In fairness, there’s a key difference between wildfire emissions of carbon dioxide and emissions from human industrial sources. “Carbon emissions from a disturbance like wildfire are not entirely comparable to those from the fossil fuel sector,” explains Brendan Rogers, a postdoc at the Woods Hole Research Center who recently co-authored a study with Veraverbeke on Alaska’s wildfires, by e-mail. “This is because over the coming years and decades, the forests will regrow after a fire and begin to re-sequester carbon from the atmosphere.”
However, researchers like Rogers and van der Werf are concerned that a trend toward more or more intense fires could upset this dynamic and lead to more carbon winding up in the atmosphere — a net increase. Van der Werf says that this is a concern “especially in the boreal region” — i.e., Alaska, Canada, Siberia — because temperatures there are increasing so quickly, potentially ramping up fire activity.
“If on average fires are bigger, more frequent, and/or more intense (like they have been in Alaska during the last 15 years), the landscape will store less carbon on average and this indeed impacts atmospheric CO2,” adds Woods Hole’s Rogers by e-mail.
And there’s another factor, which I’ve emphasized before — burning in northern regions allows more carbon emissions from permafrost, the biggest problem of all. As Northern Arizona University’s Michelle Mack explains by e-mail:
Beyond the direct carbon emissions from fire, loss of the insulating organic layer is likely to destabilize permafrost, leading to thaw, decomposition and release of soil carbon that may be hundreds to thousands of years old. These permafrost carbon stocks are irreplaceable in the current climate.
And there are still more consequences. As James Randerson, a professor of Earth sciences at the University of California Irvine, explains by e-mail, “black carbon aerosol injected into the atmosphere by boreal forest fires makes its way into the Arctic, where it darkens snow, sea ice, and the Greenland ice sheet.” That, in turn, leads to more ice melting — and a warmer Arctic.
Finally, bear in mind that Alaska only represents a small fraction of the total burning from northern fires this year. White House science adviser John Holdren recently estimated the total at 31 million acres when including fires in Canada and Russia, according to reporting in the New York Times.
Globally, wildfires in all regions contribute about 2 petagrams, or 2 billion metric tons, of carbon to the atmosphere each year, van der Werf’s research suggests (although, again, most of this is pulled back into the landscape eventually, unless fire trends change).
So in sum — Alaska’s wildfires didn’t just damage tourism or cause smoke hazards for people in cities like Fairbanks. They also emitted a pretty dramatic amount of carbon dioxide, and what’s worrisome is that this could be part of a trend.