Most of the coal and oil we mine comes from a time before microorganisms could efficiently break down lignin and cellulose. Now that such organisms exist, trees alone can only temporarily sequester carbon. I guess planting more trees gives us some small buffer, but even were it significant it's not really a long-term solution.
You are very right. We need to use every tool at our disposal over the next few decades if we are going to avoid a climate disaster, and afforestation plays a role in nearly all routes to avoiding that disaster [1].
But that leaves it in the biosphere, and new forest is vulnerable to rapid deforestation and conversion to CO2 (fires, cultural change, etc.). We would ideally shift some of that highly mobile bio-sphere sequestration to far less mobile geologic sequestration. Most likely with technology that we haven't yet invented.
[1] chapter 2, afforestation is part of AFOLU carbon dioxide removal (CDR) https://www.ipcc.ch/sr15/
If you expand forests that’s ongoing sequestration. One doesn’t count rainforests or boreal forests as “zero carbon” capture. They have an ongoing capturing capacity.
> If you expand forests that’s ongoing sequestration.
If you expand forests it's a one-time sequestration. That's my point.
> One doesn’t count rainforests or boreal forests as “zero carbon” capture. They have an ongoing capturing capacity.
Each ecosystem has a turnover time. For rainforests it's like 20 years. For tundra it's as long as 65+ years. But in a stable state these carbon "sinks" are net zero carbon capture. For every ton of carbon they capture, a ton of carbon is released through decomposition.
The problem is that we're pumping out alot of carbon: about 10GtC/year. The entire Amazon rainforest sequesters only about 100-200GtC. Actually, the biggest problem as I said is that we're pumping out carbon from a resource (Carboniferous period deposits[1]) that can never again be recreated, at least not without significant geoengineering.
[1] Carboniferous deposits occurred at a golden period, immediately after woody trees first emerged, but before microorganisms evolved that could decompose them; trees could be buried long enough to fossilize before microorganisms could release all the carbon back into the atmosphere. That can't happen today naturally, at least not at any scale that could help us.
Thank you for the well-argued and rational post. To me, buying 20 years for decarbonization sounds kind of great. So, it's a fallacy to think we could just plant trees and otherwise go on as usual. We just need to be careful about language that might feed into defeatism: planting a lot of trees is not a wasted effort, it's a great thing to do. Yes, we need to do a lot more, but every year of extra time helps a lot.
The more wood you use, the more inefficient your building methodology given the amount of energy needed for transport, construction, etc, as well as air conditioning, etc. The less wood you use, the less space you create for regrowth. (Indeed, the space taken for building a house is often space where trees could grow, so there's a very simple space trade-off at play.) And none of this factors in the huge amount of wood from demolition that we scrap every year, requiring energy to tear down, and much of which will decompose even in landfills.
Plus, a place like the United States has 0 population growth absent immigration. Are we supposed to start tearing down houses just to build new ones? That's the kind of math that begat corn ethanol.
The dynamics here are just horrible. Can we slow emissions growth this way? Sure. Can we stop growth this way? Eh... okay, maybe, since we're pretending. Can we reverse global warming, removing carbon from the atmosphere? Not a chance. The only way to turn the dynamic from zero sum to positive sum is with other, major technological advances, at which point playing games with trees and home construction would very likely be the least meaningful use of such new technology.
EDIT: Here's a study that looks at various different models for wood processing and disposal. TL;DR: See figures #2 and #3. 100 years post harvest there's at best 5% net carbon sequestration, while most models show 0% net carbon sequestered. https://www.sierraforestlegacy.org/Resources/Conservation/Fi...
You're arguing it must be a 100% solution or nothing. I doubt there are any 100% solutions. But we only need 10 10% solutions, so I wouldn't be in any hurry to reject even a 1% solution.
Oh, and also, there's always going to be a need for new construction even with 0 population growth. Better to use wood than concrete, as concrete is a large source of carbon emissions.
Concrete reabsorbs carbon over time, so the net carbon footprint dynamic is not unlike that of wood. See https://www.architectmagazine.com/technology/concrete-become... Concrete's long-term net carbon footprint is simply the fossil fuel energy input minus whatever unoxidized material we dredge up. While theoretically we could manually plant trees and manually bury them in a way to minimize decomposition, we could likewise dig holes to expose and crush unoxidized rock. The former might be marginally more efficient energy-wise than the latter, but the energy consumption dynamics of both fundamentally suck.
I agree, many small solutions can help. More efficient use of existing resources is a large reason why American per capita energy consumption has remained steady for the past decade. (At least if we ignore our outsourced carbon emissions.) But many, small efficiencies is a privilege only rich countries with strong institutions are likely to achieve. Certainly historically that has been the case. Yet such countries have enormous carbon footprints. Similarly, reforestation can be helpful in a strict sense, but our primary problem is deforestation in developing countries, and even with global warming increasing the growth of temperate and boreal forests, it's rather difficult to make up the loss of tropical forests.
More importantly, none of these measures can help nearly as much as nuclear energy or renewables like wind and solar, which are both necessary and at least theoretically sufficient on their own. I think we just need to be clear about the efficacy of various measures. By all means, plant more trees. We can certainly walk & chew gum at the same time. But when people think these activities are even remotely similarly efficacious, and when the lesser one is easier to accomplish policy-wise than the other (e.g. in a country where we've effectively already accomplished an efficient market for wood products), I worry about misdirected attention.
More specifically, we need to discard this widespread notion that trees (naturally, or even in an industrial life cycle) are perpetual carbon sinks. That's really what I was getting at by pointing out the Carboniferous period--that the fundamental dynamic of carbon sequestration by trees does not and cannot work as commonly believed. The article for this thread is interesting (though only experimentally showing what was already well predicted), but it's misguided to believe it's of any consequence in the fight against global warming. The oceans are a different matter, though I don't know how greater is the long-term sequestration potential--I don't think we understand the carbon cycle as well as we do on land; for example, we know less about the microbiota, especially on the ocean floor.
