[BitwiseFool]

>"Why cant we just plant more trees?"

We can, and we certainly should, but that does not solve the problem because those trees will eventually die and that carbon will cycle back through the biosphere. Mankind extracted a ton of carbon from the ground, where it was locked away, and we put it back into the air. People are trying to find ways of putting all that extra carbon back somewhere where it won't affect the cycles in nature. Trees just temporarily lock up carbon.

[dharma1]

If you cut down trees (sustainable forestry with selective, not clear cutting) and use the logs in durable housing construction, furniture making etc you are taking that carbon out of the loop for a hundred+ years if the housing/furniture is well looked after. Most housing could be built with timber. It might be temporary but buys us time, and trees are amazing CO2 capture machines that are cheap to scale up - they run for free on solar energy and look after themselves.

Stopping deforestation and massively boosting reforestation is one of the most effective things we can already do at scale. At this point we also need active carbon capture and significant reduction in emissions too, though - a multi-pronged approach.

[nostromo]

> those trees will eventually die and that carbon will cycle back through the biosphere.

Trees in forests are self-replicating. When one dies another grows in its place.

Yes, this isn't the only solution, but it's certainly part of the solution.

[lend000]

Yes, but the point is that there is an upper limit to the contribution, and even reforesting unrealistically vast tracts of land does not make up for carbon extracted from deeper in the crust. Growing, cutting, and burying fast growing trees deep in the Earth, then replanting them, would not have that limit (although there would be other problems keeping the land fertile).

[nostromo]

If you wanted to keep sequestering after the forest matures, just bulldoze the forest ever few years and put the logs in a cave.

You've accomplished everything other sequestration technology promises, but you've done so in a way that is environmentally friendly.

[otterley]

Better than that! Trees reproduce at a ratio much higher than 1:1.

[mabbo]

Well, most of the carbon in the ground that we're burning are long-buried trees, right? I wonder what it would take to just bury a lot of trees and let them regrow naturally.

This paper has some interesting ideas: https://cbmjournal.biomedcentral.com/articles/10.1186/1750-0...

My approach would be to find the best CO2/$ types of trees, buy them straight from the lumber industry, and sequester them in no-longer-used quarries. Just need to figure out a scalable way to ensure anaerobic conditions to help prevent CO2 release on breakdown.

[fy20]

At the time coal deposits formed the bacteria that broke down lingin and cellulose hadn't yet evolved, so just burying trees wouldn't work today as they would decay. You could probably burn the wood to produce charcoal (burning it in a low oxygen environment), and the bury that, but just cutting down a forest and burying it won't work.

[ars]

In a low oxygen, low water environment it would work fine.

For example an old coal mine and then seal it.

Old coal mines are too dangerous for humans to enter so you need some kind of robotics to load them up with trees and other biomatter to bury.

[Method-X]

This would never scale.

[mumblemumble]

I'm no chemist, but, wild guess, you might actually make things worse by favoring decomposition into methane instead of CO2.

I would think that a proper solution would require figuring out how to get all that carbon into a chemical form that is chemically stable and won't biodegrade. The ideal looks a whole lot like coal, I'd guess?

[giantg2]

Yep methane is multiple times more potent as a greenhouse gas.

[sailingparrot]

You also need to find a way to speed up tree growth rate by 10x or 100x for this solution to be effective before most of the damage is done.

[BitwiseFool]

My understanding is that when wood first appeared on Earth nothing was able to decompose all of that cellulose for millions of years until microbes evolved a way to break the molecules apart and feed on them. I don't know if simply burying the trees is enough to sequester it away now that wood decomposes so readily.

[lutorm]

Trees, unless you clearcut them (or they die off due to climate change) permanently lock up carbon. Yes, some die and decompose, but new ones grow up to take their place. It's just the total amount of biomass created that matters.

[_ph_]

Long term the dead trees might release the carbon again to the atmosphere, but we are currently facing problems over the next decades. Even if trees would only move some amount of carbon "into the future", they could buy us precious time while we deploy other solutions for the problem. And of course, one can try to permanentely capture the carbon bound by trees by not letting them burn/rot after their life.

[otterley]

Dead trees lie on the ground, with all their sequestered carbon sitting there. It's not like the carbon is going back into the atmosphere, at least not without some process like combustion. Coal is basically dead trees. Before we started extracting coal and burning it, it was harmless to the atmosphere.

[m12k]

Doesn't rotting, or being eaten by microbes or termites that eventually get eaten or die and rot eventually lead to the release of the stored carbon?

AFAIK coal is composed mostly of trees that fell back before microbes evolved that could eat through their cellulose walls, and have had millennia of underground compression to further increase their stability - basically that process isn't available naturally to trees that fall today.

[otterley]

It takes roughly twice as long for a tree to decompose as it does to grow; and trees live a lot longer than that! So over time, the net sequestration should be positive.

[redisman]

They release the carbon as the decompose or burn. Sahara sounds like a very likely place for wildfires

[r00fus]

> It's not like the carbon is going back into the atmosphere, at least not without some process like combustion.

Western USA has had a "fire season" for every year for the last like 4 years. Last year, other places like Brazil and Africa join in on the fun.

So planting trees without a robust animal/insect ecosystem to decompose them before they combust is an incomplete solution.

[shadowlight]

no. Unless the tree vaporizes or burns, none of it gets back into the air. It is for all intents and purposes a permanent lock up. Mankind is the gatekeeper of whether to unlock this carbon prison in our choice to burn oil or wood.

Trees aren't the complete solution and the reason why has nothing to do with the tree dying and releasing the carbon.

What's going on here is that plants are converting CO2 into mass. A tree that isn't growing isn't creating new mass and therefore isn't lowering carbon in the atmosphere.