Many seem to think that they’re done something great for the environment by burning wood or some other type of biomass. Aside from the particulate pollution that it creates and the potentially hazardous ash, the act of burning wood, it is said, simply releases the CO2 back into the air that the tree had absorbed during its life. It is also claimed that if another tree is planted to replace the one that was cut down for fuel, the carbon is re-absorbed and the whole thing results in no net increase in CO2. Furthermore, it is stated that the carbon would simply return to the atmosphere when the tree dies anyway, because it would decay, producing carbon dioxide and methane, which is even more potent a greenhouse gas and which eventually breaks down to CO2.
Sorry, but I just don’t buy it. It’s an overly simplistic way of looking at things.
I’m not entirely against the limited use of wood for things like pizza ovens, toasting marshmallows and building fires on cold winter nights, but that’s only because such applications are fairly small in total emissions. It should not be used as a primary fuel and is not “carbon neutral” when it is.
First and foremost, burning wood releases carbon in a matter of minutes that took years or decades to sequester. Had the tree been left to grow on its own, this carbon would continue to be sequestered for at least decades more, depending on the type of tree. Even pine trees can live for hundreds of years.
Of course all trees will eventually die, but does this mean the carbon in them is all returned to the atmosphere as carbon dioxide? Absolutely not! The wood itself may take decades more to break down and the process of decomposition may very well not result in a complete release of all carbon into the atmosphere. There are number of processes that prevent this from happening. Acidic soil, such as that found in pine forests can inhibit complete decay. Accumulation of soils and biomass can eventually compress the material into the subsoil. Eventually, much of the material reaches the state of humus, where it is stable and does not break down any further.
This same process can apply to the leaves or needles shed by the tree. Once a tree has reached full growth, it may not absorb much more carbon dioxide into its wood, but it continues to absorb carbon dioxide to produce leave. As leaves die and fall off, much of that carbon will return to the atmosphere as CO2, but not all of it. Layers and layers of leaves build up on forest floors, where an entire strata of biological material accumulates. Much of this will be reduced to carbon rich humus and will not decay further.
Even if a tree is cut down, it does not mean it will release the carbon it has accumulated back into the atmosphere. When wood is logged, it goes into any number of products, some durable, such as houses or pianos and others non-durable such as paper or pallets. If the wood is used to build a house, it may continue to exist in a stable form for centuries. Non-durable goods might seem to be the end of the road, but they’re not.
It is a popular misconception that trash in landfills decays. In fact, it only does to a relatively small degree. Garbage will decay, releasing CO2 and methane when it is first placed in a landfill, but as it is compressed and isolated from the environment, the process slows to a crawl. This is why old, capped, landfills produce less and less biogas as time goes on. Indeed, landfills are huge carbon sinks. Wood or paper can easily remain for decades, relatively undecayed. The process of compression and isolation is akin to the processes that produce fossil fuels and can result in the carbon being retained for thousands of years or more.
Even if trees were to break down completely and return the carbon dioxide to the atmosphere, this does not mean that the same applies to an entire forest. If a forest is allowed to grow without being cut down for fuel, trees will die and decay while others will grow in their place. A state of equilibrium is reached, where even if the net additional carbon dioxide absorbed is small, the amount sequestered is still enormous. However, if the trees are logged and burned, even if they are replanted, the forest never reaches the point where it is a stable sink for carbon dioxide.
Therefore, even with tree farm wood, the wood is being grown in a manner that displaces a potential carbon sink and uses wood that could otherwise go into a durable product. This is far from being carbon neutral.
Finally, it’s worth noting that wood is a critical material for building and producing numerous products. Huge areas are used for conventional logging or tree farming as is. Using wood for fuel only increases the need for producing wood for such needs. Adding the need for fuel only increases the impact and reduces the amount of naturally growing trees for us all to enjoy.
This entry was posted on Saturday, June 26th, 2010 at 8:26 pm and is filed under Bad Science. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
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