“This is exactly what we’ve been projecting to happen, both in short-term fire forecasts for this year and the longer-term patterns that can be linked to global climate change,” says Ronald Neilson, a professor at Oregon State University who also works for the US Department of Agriculture Forest Service. “You can’t look at one event such as this and say with certainty that it was caused by a changing climate, but things just like this are consistent with what the latest modelling shows.”
According to Neilson, the latest models suggest that parts of the US are experiencing longer-term precipitation patterns, with less year-to-year variability but several wet years in a row followed by several years that are drier than normal. Wet years can increase the amount of vegetation, providing a greater “fuel load” for fires in dry years.
Christine Wiedinmyer, of the US National Center for Atmospheric Research, estimates that the southern California fires released 7.9 million metric tonnes of carbon dioxide between 19th–26th October. That’s equivalent to about one quarter of the average monthly emissions from fossil fuel burning throughout California. Wiedinmyer and colleague Jason Neff at the University of Colorado use satellite observations of fires and a computer model to estimate the amount of carbon dioxide emitted based on the mass of vegetation burned. They reckon that their calculations have a margin of error of about 50% from difficulties in measuring the extent of the fire precisely and because different types of blaze emit different amounts of carbon dioxide.
On a national scale, the pair calculate that fires in the US release about 290 million metric tonnes of carbon dioxide each year – about 4–6% of the amount that the country emits by fossil fuel burning.
“A striking implication of very large wildfires is that a severe fire season lasting only one or two months can release as much carbon as the annual emissions from the entire transportation or energy sector of an individual state," they write in a paper in Carbon Balance and Management.
Of course, forests will re-grow after fires, re-absorbing the carbon dioxide released but that process may take decades. Recent research into boreal forests in Canada found that fires can transform the forest from a weak carbon sink to a weak carbon source by altering the balance of vegetation present. And fires cause other environmental concerns such as the release of large amounts of ash, destruction of topsoil and damage to wildlife and habitat – not to mention loss of human life and damage to people’s homes. Foam released by firefighters may also get into rivers, causing damage to ecosystems at a later date.
But it looks like that’s something the world is going to have to learn to deal with. The last word goes to Neilson: “In the future, catastrophic fires such as those going on now in California may simply be a normal part of the landscape.”