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Join Date: Mar 2009
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#54
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Re: Is Burning Wood Carbon-Neutral?

03/11/2009 8:22 AM

I keep hearing that wood burning is carbon neutral but this statement is generally made without looking at the actual science of CO2 release related to burning.

First of all, the assumption that burning wood is carbon neutral assumes that all of the carbon released during the burning would be released when the wood (fallen tree etc) decomposes. This is not true. In the northern Boreal forest 80% of the carbon mass is in the soil. This is less in warmer climates but still significant. When a tree decomposes, a significant amount of its carbon is sequestered in the soil.

Secondly, we are not looking at the rate of carbon sequestration that occurs when trees grow. It is very slow. It might take years to grow enough wood as I can burn in one cold night. Even if I have a wood lot, and even if the wood that is being burnt is collected from deadfalls and the woodlot is maintained. There is no way we can generate enough new growth per year to sequester the CO2 released in heating one home without huge amount of land being dedicated to a woodlot. This is not very practical for most of us. (Even if that wood were to rot naturally and release its CO2 component to the atmosphere, it is really slow, I have some firewood that has been sitting in my back yard for over ten years and while it is rotting a bit, is still pretty sound and holding onto its carbon).

Third, plants do use soil carbon when growing, not just CO2 from the air. Therefore, you would need to grow more wood than you burn (in the same time period of your burning) to replace the carbon released by your burning.

I like the term carbon rate neutral. This is an important concept for people to understand. Another concept to consider is dynamic equilibrium. The earth is in a state of dynamic equilibrium (a geomorphology term at least as I originally learned it). The process of constantly trying to maintain this equilibrium is a large driver of our weather systems (i.e.: hot air at the equator trying to equilibrate with cold air at the poles causing air movement and temperature mixing etc.). In a natural state, the amount of carbon released equates to the amount of carbon sequestered over time. Once we much about with the earth's ability to keep things in equilibrium, we see changes from what we are used to as the earth moves into a new dynamic equilibrium, i.e. rising temps due to immediate increases in CO2. I don't think burning wood is an answer to our problems or even a way to slow it down considering that we can not sequester enough carbon from burning wood to make it neutral in the short term which will cause an increase in CO2, i.e. not carbon neutral.

Don't forget the environmental devastation caused by burning too much wood in overpopulated areas of the world and the various other constituents released from a wood stove even with a catalytic converter (dioxin, polycyclic aromatic hydrocarbons, etc).

Here are some back of the envelope calculations comparing the amount of CO2 released per btu of energy produced:

Natural gas – 117.6 lbs/MMBTU

Wood – using the wood fired boiler (industrial sized) factor - 195 lbs/MMBTU

Using the factor for a wood pellet (home unit) stove - 185 lbs/MMBTU

Fuel Oils

Kerosene – 159.3 lbs/MMBTU

#2 oil – 159.3 lbs/MMBTU

#6 oil (high sulfur) – 162.7 lbs/MMBTU

Anthracite Coal – 230 lbs/MMBTU

Sorry to be a naysayer, but this is an important topic. Instead of deluding ourselves that that we are helping by burning wood or other biofuels, we should be focusing on alternative energy such as solar, wind, tidal, etc. Combined with efficiency, public transportation, etc, we could halt the excess release of CO2 that we are causing now.

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