A new study by two Colorado researchers shows that U.S. wildfires pump a significant amount of the greenhouse gas into the air each year, more than the state of Pennsylvania does. It raises questions about how useful it is to plant trees to offset rising carbon dioxide emissions and soothe environmental consciences.
Because the California wildfires occurred just as the study was about to be published, the researchers calculated how much carbon dioxide was likely to come from the devastating blazes Oct. 19-26. It's a lot: 8.7 million tons.
That's more than the state of Vermont produces in a year. And it's also more than the 6 million tons estimated by California's air control agency, which used a different calculation method.
On average, wildfires in the United States each year pump 322 million tons of carbon dioxide. That's about 5 percent of what the country emits by burning fossil fuels, such as gasoline and coal, according to the new research published online Thursday in the peer-reviewed journal Carbon Balance and Management.
"It is quite a big chunk," said study co-author Jason Neff of the University of Colorado at Boulder. But he adds: "It's nothing compared to our fossil fuels burning."
Mostly when scientists look at carbon dioxide emissions, they spend their time on the stuff that man adds to power industrial life. But Neff and Christine Wiedinmyer at the National Center for Atmospheric Research in Boulder, Colo., looked at forests, which act as a sponge and absorb some of the carbon dioxide, but which also burn and produce it.
"The problem is that what goes in, comes out," Neff said.
In recent years, some people who want to compensate for their personal contributions to global warming (from driving gas-guzzling cars or heating huge houses) have paid groups to plant trees to soak up that extra carbon in the air. It's called a carbon offset.
Over several decades or centuries, replanted trees will capture some of the gas, but the first few decades it will be at a reduced rate, Wiedinmyer said.
"There's a real danger here that in the offsetting program you feel you've done your bit," said University of Victoria climate scientist Andrew Weaver, who wasn't part of the study. "You've got to be a little bit more creative than to think that you're going to solve global warming by planting trees."
In previous studies, scientists have shown that a general increase in American wildfires - but no one event - is linked to global warming. That raises the possibility of a self-feeding cycle, Wiedinmyer said.
The scientists used satellite imagery, computer models and combustion rates to determine how much carbon dioxide is released during a fire, Wiedinmyer said.
Last week, the California Air Resources Board estimated that just under 6 million tons of carbon dioxide were released by the recent fires. The board estimates that for every acre burned, the carbon dioxide emissions are equivalent to two cars driven for a year, said board spokesman Stanley Young. More than half a million acres have burned in Southern California.
Young and Wiedinmyer said estimates do vary widely on scientific method.
The paper finds remarkable differences state by state and month by month. August is the worst month for carbon dioxide emissions from fires.
The Western continental United States is responsible for more than one-third of the country's carbon dioxide from fires. But Alaska is king. Alaskan fires produce twice as much of the greenhouse gas than burning fossil fuels in that state. Alaskan fires make up 27 percent of the nation's yearly fire-related carbon dioxide emissions.
In the Lower 48, California, Oregon, Idaho, Washington, Louisiana, Montana, Georgia, Alabama, Florida, and Texas are top 10 emitters of carbon dioxide through forest fires.