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 Home >> Eco Scope >> Lifestyle
 
 
 Is wood burning carbon neutral?
By 4ecotips
Published on November 26, 2007, 1:39 pm

“It doesn’t really work” - is one opinion

I am not trying to be a troll or anything else, writes Mike Lynn, but I have been thinking about various ways of being carbon neutral and I am becoming more concerned about the general characterisation of wood burning as carbon neutral. From a mass-balance point of view, it doesn't really work! I will explain:

CALCULATED
Natural Gas releases less CO2 per btu than burning wood.

Back of the envelope calculations using some emission factors from EPA on CO2 emissions from different fuels:

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

QUESTION
Burning wood releases more CO2 per btu than Natural Gas. Is however the difference in the amount of CO2 released between the two fuels offset by the amount of carbon sequestered by the forest/woodlot where the firewood was taken such that burning wood releases less CO2 to the atmosphere than other fuels and has an immediate positive effect on the atmospheric CO2 balance?

(As long as a woodlot/forest is managed correctly, the wood removed from the woodlot will be replaced making using it “carbon-neutral”. However, it may take so long for the wood to be re-grown, that burning wood from the wood lot each year will actually cause an increase in CO2 in the atmosphere. The condition we should actually be concerned about would be better described as “carbon-rate neutral”, i.e. what we burn each year, must be replaced in a shore time or we will cause an increase in greenhouse gasses. This is hopefully explained below:

KNOWN
Trees drop carbon containing materials (leaves, branches, twigs, seeds, etc) to the forest floor every season.

These materials will “rot” and will release CO2 as they do so.

Not all carbon released by waste organic material is released as CO2 to the atmosphere. A potentially significant amount of carbon becomes part of the soil mass (is sequestered by the soil).

Trees sequester carbon (CO2) as they grow by using respiration to lock up the carbon in the wood (and leaves, etc) produced each season.

If you burn wood taken from the forest, it may eventually be replaced by growth in the forest.

UNKOWN
The percent of the carbon in organic waste or rotting wood that is sequestered by the soil (i.e. becomes part of the soil) versus the percent released to the atmosphere.

The rate of CO2 release by “rotting” twigs, branches leaves, etc. For example: a piece of firewood used to block runoff on part of my driveway has been sitting there for over ten years with only a little bit of rot. This therefore has not released much CO2 and a tree somewhere has begun to replace the mass of the piece of firewood and sequester the CO2 being released by the rotting process. If this piece of wood had been burned, its full component of CO2 would have been released immediately.

How much of the annual tree growth is “used up” sequestering the annual release of CO2 from rotting materials (it is likely there is almost an annual balance between the CO2 released by rotting leaves and sequestered by new leaf growth, but does the annual increase of wood mass equal the amount of wood that rots on the ground each year)?

ASSUMPTION
The natural forest system is in a dynamic equilibrium condition between the amount of carbon released and the amount of carbon sequestered by the new growth and soil.

In a natural forest, there is actually probably more carbon sequestered both in the soil and by tree growth than what is released by “rotting” of wood and other organic material each year.

Looking at it “overall” this imbalance however has probably been “used up” at least in part by sequestering CO2 released by other natural CO2 releases such as forest fires and volcanic activity (yes this does occur every year and does release a lot of material to the atmosphere each year).

These thoughts do not include other CO2 producers and sequestration activities (such as ocean plankton etc). However, the earth has been in a dynamic equilibrium where over time, the releases of CO2 are balanced by the natural sequestration of CO2 (some years there will be an increase in CO2 in the atmosphere and others a decrease in CO2 which is why it is a “Dynamic equilibrium”.

There are also natural CO2 cycles on the geologic time scale not considered here.

As we muck about with the atmosphere and release more CO2 than can be sequestered by existing methods, the system is no longer in equilibrium and we increase CO2 in the atmosphere which in turn creates the Greenhouse effect.

CARBON CYCLE LAG TIME
This is significant and I have seen nothing written about this but I believe it makes wood burning not carbon neutral. If year after year, we burn more mass than is replaced that year (and subsequently the CO2 sequestered by the growth/increase in mass), the amount of CO2 in the atmosphere will increase because at a constant rate of burning we can not ever replace enough of the wood mass to sequester the carbon and even when looking at it over a long time, we will not reach equilibrium.

I apologise if it seems that this message is intended to create any controversy, but I am seriously concerned about how wood burning is being characterised.

More information: www.the-tree.org.uk



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