Fire Can Be Good For Global Warming

Scientists have calculated that it actually makes sense to start intentional fires to keep down debris and undergrowth. Even though these prescribed fires do put carbon into the atmosphere, the scientists calculate it's less than what would go up in big wildfires.

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This is WEEKEND EDITION from NPR News. I'm Liane Hansen.

People who manage forests long have debated how much to intentionally burn them. Intentional fires can remove some of the forest debris that fuels bigger, uncontrolled wildfires. Now there's a new wrinkle in the debate because forests soak up climate-warming carbon dioxide, scientists are trying to figure out whether small fires make forests better carbon collectors.

NPR's Christopher Joyce has more.

CHRISTOPHER JOYCE: The kind of fire we're talking about here is one that people intentionally set. I watched a so-called prescribed burn in a forest in Brazil, along with fire ecologist Jennifer Balch.

Dr. JENNIFER BALCH (Fire Ecologist): The plan is to measure the fire and see where it's at. We're going to map the fire lines.

JOYCE: It sounds hot and it is hot. And as soon as they start the fire, even though the wind's blowing the other direction, you can feel the heat. The important thing is to keep moving with the fire and watch out for snakes.

Balch is an ecologist with the National Center for Ecological Analysis and Synthesis, who studies how forest fires burn. She says for decades forest managers in the U.S. have focused on suppressing fires. As a result, a lot of forests that used to burn naturally every now and then are choked with downed wood and undergrowth.

Dr. BALCH: It's kind of like a jack-in-a-box phenomenon where if you keep storing carbon in forests that historically have burned, eventually you're going to get a surprise if you don't burn at at least semi-frequent intervals.

JOYCE: The surprise being a really whopping big wildfire. In addition to what it destroys on the ground, a wildfire emits thousands of tons of carbon that eventually warm the atmosphere. Balch says the government spends four times as much money every year fighting fires than it does on preventive measures, such as controlled burns.

So, many ecologists have been pushing for more prescribed fires. To keep them small, crews surround the burn area with fire brakes - essentially paths that are scraped clean of anything flammable. Crews also make sure the fire isn't started on a dry windy day.

Christine Wiedinmyer is a scientist at the National Center for Atmospheric Research.

Dr. CHRISTINE WIEDINMYER (Scientist, National Center for Atmospheric Research): Prescribed burning, if it's done correctly, you only burn the understory and you leave a lot of trees living, and therefore, they can continue to sequester carbon, as opposed to a large wildfire that wipes everything out.

JOYCE: But one nagging question has been which puts more carbon up into the atmosphere, a series of small, prescribed burns or the occasional big wildfire? So, Wiedinmyer developed a computer model to calculate that, using the record of both kinds of fires in the western U.S. from 2001 to 2008. She published the results in the journal Environmental Science and Technology. Although the numbers are rough, the outcome is clear: prescribed fires do emit carbon but much less than the wildfires they prevent.

Dr. WIEDINMYER: We could reduce the emissions from wildfires by as much as 25 percent. And fires emit a significant amount of CO2 to the atmosphere.

JOYCE: Wiedinmyer points out that big wildfires also create more smog, ozone and particulate pollution that are not only annoying but cause health problems for people living nearby. Wiedinmyer notes, however, that these same people aren't always eager to see prescribed fires in their neighborhood either.

Dr. WIEDINMYER: I live near an area that has regular prescribed burning and people, if they're unaware of what's going on, they get a little worried.

JOYCE: Fire ecologists say the nation needs a plan for prescribed burns because forests are becoming valuable carbon banks. Industries and even individuals can now offset their own carbon emissions by paying someone else to preserve or grow forests. But that could turn many forests into overgrown tinderboxes and even discourage prescribed burns, since those fires would in effect be like burning part of someone's bank account.

Christopher Joyce, NPR News.

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