An item on the BBC TV news about carbon emissions included the throw-away remark about wood-burning stoves being carbon neutral, trees ‘lock in’ carbon from the atmosphere and therefore do not add to emissions. I am not sure I get this. Carbon is carbon. Any tree you cut down and burn will release it’s carbon. Even if you replace the burned tree with a new tree, it is surely only going to lock in the carbon the felled tree would have done had it been left alone. Only if you replace the burned tree with 2 new trees will it become neutral, so why is that different from burning fossil fuel and planting an extra tree? What factor am I missing?
1-2=0?
The tree took 1 tree worth of carbon out of the atmosphere when it grew. Burning it releases one tree worth. Neutral.
Burning coal or oil takes carbon that was in the ground and releases it. Not neutral.
Time.
Burning trees is “Carbon Neutral” over decades - all the carbon in the tree came from the atmosphere recently, unlike fossil fuels, where the carbon came from the atmosphere millions of years ago. So, if you only burn trees, and replace them, the average CO2 level in the atmosphere doesn’t change.
The way trees “lock in” carbon is by growing and incorporating carbon into its structures. So the cycle is something like this:[ol][]Plant a seed.[]Seed grows into a tree, taking some amount of carbon out of the air and putting it into its trunk, branches, and leaves.[*]Cut down the tree and burn the trunk, branches and leaves. This releases the carbon contained in the tree into the atmosphere.[/ol]Net result is that some amount of carbon is taken out of the atmosphere as the tree grows, and the same amount is released when you burn it.
I think they are stretching the term ‘carbon-neutral’ when they use it to refer to wood burning. The only ways it could be used that way, in my opinion, is if you planted the trees yourself for the express purpose of burning them and then waited 20-40 years for them to mature. Counting on a sapling, planted today to replace a fallen tree, to sequester all the carbon you released from burning the tree, would place you in a carbon debt that wouldn’t be paid off until the sapling has grown to full height.
However, wood is a renewable resourse unlike petroleum, you can always plant more trees to replace the ones you use… you can’t plant more coal or oil, once it’s used, it’s pretty much gone forever, and any carbon it contained is released.
Everything is carbon-neutral in the long term, including burning both trees and oil. Oil, however, puts carbon back in the atmosphere which has been out longer, disrupting the equilibrium.
Valete,
Vox Imperatoris
What about the ash?
Assuming this isn’t a pun, the ash is non-burnable material, usually mineral-based. You may have incomplete burning of wood in a fireplace, but if you burn wood in a pure oxygen atmosphere, you will still have a small amount of residue. After all, the tree isn’t 100% C, O, & H.
If I cut down a tree it stops absorbing carbon. If I plant a new tree it absorbs the carbon the old tree would have absorbed had I not cut it down. The same amount of carbon is released whether I burned fossil or new fuel. The same number of trees are growing so the same amount of carbon is absorbed. The result is the same amount of carbon in the atmosphere regardless of the source. Only if we end up with more trees growing is there a benefit and we can plant more trees even if we burn coal.
Poorly-worded question.
Does the ash contain C? (If so, wood-burning is better than carbon-neutral I think.)
Visualize the carbon in the atmosphere as a pile of beans. A mature tree contains 1 beans’ worth of carbon, so you move 1 bean from the atmosphere’s pile to the tree’s pile. Now, you cut down the tree and burn it, so the bean goes back into the Atmosphere’s pile. If you cut down trees and burn them faster than you grow them, the Atmosphere’s pile increases. If you grow trees faster than you burn them, the Atmosphere’s pile decreases.
If you burn fossil fuels, the CO2 in the Atmosphere increases, unless you plant enough trees to compensate.
It’s an accounting problem.
There is carbon in ash, but I doubt it is significant. Some of the ash is in the form of carbonates. There may also be incompletely burned carbon if there wasn’t enough oxygen. Calling burning wood less than carbon neutral still doesn’t sit right with me.
But you are removing one absorber and just replacing it with another - no net change in absorption rate.
A forest can easily be self-regenerating - new trees grow from seed and shoots to replace the trees that die or are killed by wind & weather. You can harvest wood from such a forest (the simplest example would be collecting downed limbs) without any net effect on the forest’s ability to regenerate.
If you burn such harvested wood you are actually burning what otherwise would have oxidized slowly through decay. In either case, the oxidation is carbon-neutral and does not require that you ever plant a tree or wait for it to mature.
IOW, if you look at a forest rather than at individual trees, it’s easy to see how burning wood can be carbon-neutral over a short time.
How is that not neutral?
Sure, we can continue planting more and more trees to lock in the carbon burned from fossil fuels. But sooner or later we’re going to run out of available real estate for all these trees, as the required number keeps increasing for every amount of carbon that we take from below the surface and pump into the atmosphere.
On the other hand, if you just burn a tree, that only releases the carbon that would have escaped anyway when the tree died & decomposed naturally.
Option 1:
Burn 1 tree’s equivalent of coal
Leave tree standing to carry on absorbing carbon
net result: 1 trees worth of carbon added to atmosphere + 1 trees worth of absorption.
Option 2:
Cut down 1 tree and burn it
Plant new tree in place of cut down tree
net result: 1 trees worth of carbon added to atmosphere + 1 trees worth of absorption.
Saplings store much less carbon in a year than an older tree. The sapling is not a direct replacement for a large tree. You burn a certain amount of carbon for heating from whatever source. I’ll say oil. The sapling is taking less carbon from the atmosphere, but the older trees you didn’t burn may use all that carbon you released burning oil. It’s not so simple is it?
Make that:
Option1
Net result: 1 tree’s worth of carbon added to atmosphere + 1 tree’s worth of absorption + 1 tree’s worth of carbon added to atmosphere when tree eventually decays = 1 tree’s worth net increase in carbon in atmosphere
You’re not extending your example fully. Assume (for example) that a person needs 1 tree’s worth of energy per year, and a tree takes 1 year to grow to maturity.
To be carbon-neutral at the end of 10 years, option 1 requires 10 simultaneous new trees to exist, while option 2 only requires one tree. At the end of a thousand years, option 1 requires 1,000 simultaneous trees, while option 2 still only requires a single tree.