This California forest fire season so far has been exceptional, producing thousands of fires – including one that, at nearly a million acres, is the largest single fire in the state’s history – and emitting so much smoke that air quality has been compromised thousands of miles one way.
Forest fires can also have a global impact on the climate, as burning vegetation releases carbon dioxide, which warms the planet. And from June to August, California fires emitted twice as much CO2 as in the same period last year and far more than any other summer in nearly two decades.
This is the conclusion reached by the Copernicus Atmospheric Monitoring Service, an agency financed by the European Union, which estimates emissions on the basis of satellite measurements available since 2003. In the three months, the California fires were said to have released more than 75 million tons of carbon dioxide.
That is a small amount compared to the annual global CO2 emissions from burning fossil fuels, which are expected to be around 33 billion tons this year. And most of the CO2 emitted by forest fires can be offset over time as the vegetation that repopulates burned areas uses CO2 to grow. However, any additional amount of CO2 in the atmosphere is contributing to warming.
According to estimates by the agency, fires in the western United States released 130 million tons of CO2 this summer. That included about 17 million tons in Oregon, more than ten times the amount released last year. The bootleg fire, which burned more than 400,000 acres in July and August, was one of the largest in Oregon history. The Dixie Fire in Northern California is the largest in the state.
Hot summer temperatures in much of the west, coupled with severe drought, made the fires grow rapidly and sometimes consumed tens of thousands of acres in a matter of hours.
“The soil is drier and the vegetation is drier,” said Mark Parrington, senior scientist and forest fire expert with the Copernicus Atmosphere Monitoring Service. “Adding drought on top of that accelerates the extent of the fire.”
So far, California wildfires have burned approximately 2.3 million acres, which is lower than last year’s total at this point. Dr. However, Parrington said emissions were higher from June to August this year, as severe fires generally broke out earlier than last year due to the drought.
The forest fire season has been severe and emissions have set records in other parts of the northern hemisphere as well, the agency said.
There were major fires in western Canada and the Mediterranean, including one in Greece that grew from a few hectares to more than 120,000 hectares in less than three weeks.
In the Sakha Republic in northeast Siberia, where large summer fires are not uncommon, this summer was particularly bad as severe fires started as early as June.
The burned area in Sacha is much larger than that in California, and as a result the emissions are much higher. The authority estimated the CO2 emissions in the three months at more than 750 million tons, twice as much as in the previous year.
Most of the fires in Siberia were below the Arctic Circle, unlike last year when much of the area burned was in the Arctic. This year, forest fires in the Arctic released around 65 million tons of CO2 in the summer, the agency said.
Copernicus uses data from sensors on several NASA satellites that measure surface brightness temperatures in near real time. It then looks for deviations from normal temperatures that are indicative of a fire and estimates how much energy the fire is radiating. From this, it uses information about types of vegetation to estimate how much carbon dioxide and other gases are emitted.
Other groups estimate fire emissions after the end of the season using aerial or satellite images of fire scars and other data. Dr. Parrington said his agency’s past estimates compare “pretty well” with others.