Photo: John Fowler/Flickr
This is pretty nitty gritty and really interesting: Researchers at the Los Alamos National Laboratory have found that, due misunderstanding of the composition of the pollution cause by wildfires, current climate models are likely underestimating their contribution to global warming.
This new analysis, published in Nature Communications, shows that the carbon particles emitted by wildfires are very different than is assumed in climate models, with so-called tar balls (obviously different than the tar balls associated with oil spills ...) being 10 times more abundant than ordinary soot.
The current assumption with wildfires is that though the black carbon soot they spew into the atmosphere helps warm the climate—as does black carbon soot from open-air cooking stoves, from older diesel engines, and so forth—this warming is pretty much cancelled out by other aerosol emissions from the fire that results in cooling.
It turns out though, the scientists discovered after examining what happened in the 2011 Las Conchas fire that threatened their own laboratory, that tar balls really are the dominant emission in wildfires.
Manvendra Dubey, a senior scientist at Los Alamos, explains:
Tar balls can absorb sunlight at shorter blue and ultraviolet wavelengths and can cause substantial warming. Furthermore, organic coatings on soot act like lenses that focus sunlight, amplifying the absorption and warming by soot by a factor of 2 or more. This has a huge impact on how they should be treated in computer models.
Field-emission scanning electron microscope images of four different categories of soot particles: (a) embedded, (b) partly coated, (c) bare and (d) with inclusions. Approximately 50% of the ambient soot particles are embedded, 34% are partly coated and 12% have inclusions. Only 4% of the particles are bare soot (not coated or very thinly coated). Scale bars, 500 nm. Right, spherical tar balls dominate in the emissions. Image and caption: Los Alamos National Laboratory
Though there are many factors in how large wildfires can get—with policy on how we have dealt with fires playing a significant part—climate change itself is predicted to increase them. A 2011 report from the National Research Council showed that for every 1.8°C rise in temperature the total area burned by wildfires would increase 380 percent. Older research, now dating back a decade but widely cited, shows that the seasonal severity rating for fires across most of North America is likely to increase 10 to 50 percent by 2050, also indicating the likelihood for increased forest fire activity.
As for how much fires are increasing, head of the US Forest Service Tom Tidwell told Congress in early June, "On average, wildfires burn twice as many acres each year as compared to 40 years ago. Last year, the fires were massive in size, coinciding with increased temperatures and early snow melt in the West."
Again, not all of that increase can be attributed to climate change, but whatever the exact mix of causes behind past and future increase in wildfires, it only amplifies what the Los Alamos research shows—wildfires are bigger deal for predicting climate change than we currently assume.