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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

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