It seems that nothing is simple. We all know the environmental damage caused by heating our homes directly or indirectly with fossil fuels. So what about cozying up to a wood stove? Nothing could be more renewable than wood, at least if it is sustainably grown. Surely that’s as green as it gets?
As we said, nothing is simple.
Wood is never completely burned in a home stove or fireplace. Some of the residue is left as ash, but the rest goes up the chimney, much of it as soot. If you’ve ever tried and tried to wash soot off fabric, you’ll understand its other name: black carbon.
Black carbon is not a greenhouse gas, but it is carbon’s accomplice in global warming.
In fact, it may be the second or third biggest culprit, after carbon dioxide (CO2) and (perhaps) methane.
Soot absorbs and scatters solar radiation, increasing the heat captured, and sometimes affecting local cloud formation and precipitation.
Soot particles travel long distances in brown clouds, mixing with other aerosolized particles, like sulfates, nitrates and fly ash.
When it lands on snow, it increases heat absorption, leading to accelerated melting.
On the other hand, soot prevents sunlight from reaching the earth, resulting in “global dimming”.
Soot also affects local air quality, potentially harming human health, and it can be a cause of great enmity between neighbours.
As it is difficult to quantify all the effects of soot, its net impact on climate is not yet clear, especially in areas without snow.
However, the the United Nations Framework Convention on Climate Change (UNFCCC) calls for an integrated approach, controlling both greenhouse gases and aerosols like soot.
This should fight both climate change and air pollution/ smog.
Developing nations are the major sources of soot, but the rich world has considerable room for improvement.
Approximately 20% of soot emissions are from biofuels (e.g., wood, dung, crop residue), 40% from fossil fuels (e.g., coal, diesel), and 40% from open biomass burning (e.g., forest fires, crop residue burning).
The good news about soot has two parts:
First, reducing soot would have relatively quick impact, because soot is washed out of the air in a few weeks, unlike conventional greenhouse gases that can cause warming for 100 years.
Second, there are many effective technologies for reducing soot. For example, diesel-powered vehicles can be retrofitted with soot filters. Great progress is being made in many poor countries, helping women switch to solar cookers or more efficient stoves. Some such programs are being paid for through carbon offset programs. In Canada, soot emissions are indirectly regulated and minimized through provincial air quality standards that limit emissions of small particulates, including PM10.
As for your wood-burning stove? A little care and attention will go a long way. You can reduce the amount of wood you need by keeping the room draft free and well insulated. Commercial firelogs produce less soot and other emissions than wood. More efficient stoves produce far more heat and less soot, smoke and odour – if yours is not EPA-certified, consider replacing it.
Finally, use best practices – burn small pieces of clean, dry wood, preferably a mix of sustainably grown hardwoods and softwoods; don’t overload the stove; burn the fire hot; keep the flue clean; remove ashes frequently.
And stay cozy.
By Jackie Campbell and Dianne Saxe
{ 3 comments… read them below or add one }
I am doing some research into soot and global warming and the extent to which this new knowledge affects the global warming impact of residential wood heating as practiced in North America. The article I'm working on should be published at The Woodpile next week. See:
http://woodheat.org/woodpile/
One thing I have learned is that the soot emission researchers make a distinction between biofuels, by which they mean bio diesel and ethanol, and biomass burning, by which they mean burning wood or dung for cooking, and brush and stubble burning in agriculture. The text of your article doesn't use the term that way.
I have also learned that about 25 to 35 percent of worldwide soot emissions are from China and India and are mainly from millions of inefficient cooking fires and agricultural open burning. And Marc Jacobson, one of the main researchers in the field says that “About half of the U.S. black carbon in particles smaller than [PM2.5] is from fossil fuel sources. The rest is from area sources; agricultural fires, structural fires, slash/prescribed burning forest wildfires, unpaved road dust, paved road dust, and construction dust, according to the 2002 U.S. National Emissions Inventory.”
Jacobson doesn't even mention wood burned for energy, mainly because it is a tiny contributor. Nevertheless, it is important that we reduce to the extent possible the environmental impacts of all energy sources. As you point out, advanced technology wood stoves dramatically reduce particulate emissions, including soot. While the investigation of the soot issue is still in its infancy, indications now are that heating with wood in modern equipment actually produces a net reduction in global warming.
The soot issue is complicated, but that hasn't stopped people who want to see residential wood heating banned in Canada and the U.S. from distorting the available information to serve their own interests. I should point out that I was alerted to your article by one of those activists. See:
http://woodsmokeworld.spaces.live.com/blog/cns!66…
John
Dear John,
Thank you very much for your swift and helpful reply. We wrote the article partly to make sure we could honourably use our own wood stove, Intrepid II, and have also decided that we can.
Best wishes
Dianne
Very informative article.Thanks.
If trees are felled or purposely grown to provide firewood then this is going to contribute to global warming. If the tree has died of natural causes then it would release the CO2 and burning it is simply speeding up the release of the gas.
Personally I love open fires, unfortunately here it's central heating but at one of my other houses it's all open fires. It's very remote and there's woodland and forest all around with an abundant supply of casualty timber, there's a massive woodpile and come the New Year we'll be sat round roaring open fires (hopefully with deep snow outside). All the timber we burn there is casualty timber and in addition, we've planted several hundred trees (not to be burned) which more than offset any carbon emissions.
If you have an open fire yourself burn casualty timber (ask the landowners permission first if removing from private land) rather than commercially grown timber. If you do have to buy in firewood then offset what you burn by planting some trees.
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