My brother recently bought a fireplace insert and in the glossy brochure, the company tried to quell the buyer's concern that burning wood might be bad for the environment. They said that trees are "carbon neutral". That is, don't worry, trees absorb carbon dioxide while they're alive, and when you burn the lumber, you're just releasing the carbon dioxide back into the atmosphere. So it's an even swap. That's supposed to make it ok. I didn't quite buy it.
I did some investigating and concluded that this is in fact a true statement, but it's not simply ok. If you clean up highway litter and then go back the next day and dump it again, you're garbage neutral, but you defeated the purpose and benefit of the clean up. Trees absorb carbon dioxide and provide an ecological service. Dumping the CO2 back into the air doesn't make it ok or a win.
If a tree dies or is harvested, the carbon remains locked. Even as the tree decomposes, the carbon get deposited in the ground. Think of the millions of years of growth that created fossil fuel oil and natural gas. That carbon deposit is stored and then released as CO2 into the air when the fossil fuel burned. Is it ok to call burning gasoline as "carbon neutral". How about if you see a car in front of you wearing a bumper sticker that says, "I'm carbon neutral"? Do you really agree with that?
The question the fireplace insert company should be answering is how clean is wood compared to other fuels. My brother needs to heat his house so something is going to get burned (he doesn't have solar arrays or wind or any alternative energy sources). So does his insert burn wood cleaner than oil in his furnace? I think it does. They should also be talking about cost per therm of wood vs oil or NG. The brochure did talk about efficiency of burning wood and how it used a non-catalytic system to re-burn the smoke resulting in much cleaner chimney exhaust. Wood is also a renewable fuel source and reduces dependence on oil. So he has a good system going. But don't try to make me feel better with "carbon neutral".
Interestingly a 2007 article on research done at Lawrence Livermore Labs challenged that the carbon offset scheme of planting trees to absorb CO2 only works if tree are planted in the tropics. Elsewhere, you're just adding to global warming. In their simulation of removing all the world's trees, the global temperature DROPPED 0.3 degrees celsius. Why? Forests are dark and besides absorbing CO2, they also absorb sunlight and heat the earth. Depending on where the trees are, they do more harm in heating the earth than the CO2 they absorb.
If you localize this simulation, the rain forests do more to remove CO2 than heat the earth. Trees in the temperate and polar zones don't pull their weight. Without them, the snow would reflect solar radiation and the planet would be cooler. But even this study can't be taken at summary value. The details unveil more. The research details indicate that the warming effect of trees planted in temperate zones only begins once a mature (closed) canopy is established after 40 or more years. If the trees are harvested prior to this (and ideally used as timber, meaning it is not burned) and the ground replanted with saplings, the forest never develops into the dense canopy that has the described warming effect. If the lumber is burned, we're back to carbon neutral. It's a very complicated equation and balance. Throughout this carbon ecosystem, people are the ones who mess up the math.