Behind the News

Those Complicated California Wildfires

Journalists, scientists analyze carbon emissions

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It’s almost inevitable these days: from hurricanes, to drought, to wildfires, people want to know (and journalists can’t help asking) if these natural disasters are the product of man-made global warming.

It’s hard to fault all those guilty consciences out there. Humans have grown hyper-aware of our individual and collective impacts on the environment as the result of daily news coverage chronicling environmental degradation. So when the southern California wildfires riveted the nation two weeks ago, it did not take long for reporters to wonder, Is this the fault of our greenhouse gas emissions?

Fortunately, many journalists have learned the quick answer to this question by repeating the now common refrain: it is impossible to ascribe any single meteorological or geological event (read catastrophe) to global warming. But that doesn’t mean there is no connection, or that there are not other ways for the press to explore the relation between natural disasters and the earth’s climate.

Two scientific studies released this week, one in the journal Nature and the other in the online journal Carbon Balance and Management, analyze carbon dioxide (a leading greenhouse gas) emissions generated by wildfires (trees absorb carbon dioxide as they grow and release it in death as they burn or decompose).

Neither of the two studies has generated much media coverage, and not a single journalist appears to have covered both in the same article. The study in Carbon Balance and Management, authored by researchers at National Center for Atmospheric Research and the University of Colorado at Boulder, concludes that the fires in southern California will “belch,” as Greenwire put it, 8.7 million tons of carbon dioxide into the atmosphere. Some reports, such as one from the Associated Press, have it that this is equal to the total vehicle and power plant emissions the Golden State produces in a week. Others have it that the fires are emitting more carbon than some states’ automobiles do in an entire year.

Either way, it’s a lot, and problematic, too, especially if one considers the Nature study. This report, authored by a research team at the University of Madison, Wisconsin, concludes that a million-square-kilometer swath of boreal forest in northern Canada has changed from a weak carbon sink (net absorption) to weak carbon source (net release). The reason for this, according the scientists, is the growing number and size of wildfires in the region. And the reason for the fires, they add, is global warming.

Yesterday, an article in The San Diego-Union Tribune did not, paradoxically, mention either of the studies directly, but seemed to encapsulate and synthesize the conclusions of each:

There are growing concerns among scientists that fires - not just here but around the world - are part of a spiraling and destructive feedback loop: Hot, dry weather caused by climate change increases the frequency and ferocity of wildfires. These fires release into the atmosphere ever-larger amounts of particulates, pollutants and greenhouse gases that, in turn, result in even hotter, drier weather and more fires.

On average, wildfires produce about 4 to 6 percent of the total fossil fuel emissions in the United States each year. But it is difficult to measure the exact emissions of some fires, or to know the long-term environmental impact of those emissions. Computer models used to estimate these fiery effusions have a high degree of uncertainty. “Everyone acknowledges the measurement of CO2 and other greenhouse gases from wildfires is an inexact science - to put it mildly,” in Greenwire’s words.

The Carbon Balance and Management study that calculated emissions from the southern California fires clearly notes its results have a 50 percent margin of error due to uncertainties about the blazes’ extent, fuel load, other factors. This important detail should have made it into the Associated Press article, but did not. Author Seth Borenstein does note, however, that the California Air Resources Board put the wildfires’ emissions at only 6 million tons of carbon dioxide, rather than the 8.7 estimated in the journal study.

The Nature study of Canada’s boreal forest turning from carbon sink to carbon source is less uncertain than the numbers on the California fires. But there are unanswered questions about where the effects of more fires in that region fit into the worldwide picture. The research team concludes that the shift is an indirect consequence of global warming, but the CanWest News Service quotes the lead author saying that he is “reluctant” to extrapolate the results to other parts of the boreal forest, outside the area studied.

Assessing the aggregate environmental impact of wildfires around the globe is incredibly complicated. Clouds of particulate matter, such as those produced by large burns, were once thought to have a net cooling effect, and only recently have scientific reports tipped toward warming. Yesterday’s San Diego Union-Tribune article - which, again, strangely does not mention either of the journal studies - does a good job of laying out the many variables in wildfire research. “As a source of pollutants linked to global air pollution and climate change,” the article concludes, “human activity is far more problematic than nature.”

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