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Comment by InvaderFizz | Hacker News Reader

The problem with plant based sequestration is that it is a net neutral proposition unless you can bury the plants. All the talk about forests being so great(and they are, just not as carbon sinks) ignores the complete lifecycle, which is only as negative as the sustained volume of the forest, assuming you started from just dirt. If that forest ever burns, it's all back in the atmosphere again.

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This might be true of conventional crops like corn or soy but this article [1] implies kelp farming in oceans could sequester carbon from the atmosphere for a long time.

"So the kelp will sink to the ocean bottom in the sediment, and become, essentially, part of the ocean floor..."

1.https://www.npr.org/2021/03/01/970670565/run-the-oil-industr...

Of course there is always the possibility that things could burn but forests that burn do grow back eventually. Plant-based sequestration should not be written off. A planet covered by X% of forest vs Y% where X%>Y% has more sequestered carbon. If that X% is long-term stable, i.e. if the forests are preserved and curated on a long-term basis, then so is that carbon. Forests are also an enjoyable natural environment for humans, which is an added bonus.

When we say "plant based sequestration" we are (I for one am) not talking forests. Carbon sequestration in forests is wilfully ignoring the economic and practical drawbacks:

Forests only sequester carbon as they grow. After that they are carbon neutral. You end up with land that cannot be used for any economic purpose. (The creatures and plants that live in it have a value too, but that is not part of this argument).

After that, at some point, in a year, ten years, a hundred years, the forest burns. And all the carbon is released.

A pointless waste of time. We do it because we are obsessed with things we can count (one tree, two trees....) and fixated on the short term.

There is a better way: https://www.sciencedirect.com/science/article/abs/pii/S00167...

Increase depth of top soil all over our agricultural land. It increases productivity and sequesters carbon. But it has no profit centre and is hard to measure, and given our "big man" capitalist culture that is the problem.

We really must stop producing CO2. That is the only answer that does not steal the future from our children

> Forests only sequester carbon as they grow. After that they are carbon neutral. You end up with land that cannot be used for any economic purpose. (The creatures and plants that live in it have a value too, but that is not part of this argument).

I will be paraphrasing the science articles I have read lately...

Planting new trees on bare land does not work to capture CO2. So if you deforest an area and then re-plant, you put a lot of extra CO2 into the atmosphere. Like 30% of the trees you harvest go into durable things (like houses) and the rest will decompose and release its carbon. After you leave the ground bare, it starts spewing CO2 from the soil. This is a major carbon source. New trees you plant will EVENTUALLY soak up more CO2, but canopy closure needs to happen before that can happen. Since the young trees are planted with considerable spacing, the soil CO2 source outpaces the tree CO2 sink for many years before the balance shifts.

Mature forests throughout history probably did tend to be carbon neutral on average, yes. This is ignoring ecological changes... like... maybe forest conversion to other landscapes and fires were balanced by healthy forest uptake. I digress.

These are not normal times, and CO2 concentration is very high. Because of that, old-growth or mature forests may be significant sinks of CO2. The best strategy for us to draw down more with forests is to leave as much mature forest untouched as we can.

burn or decompose same thing, trees are a buffer not a solution, unless you cut down, bury deep, then regrow.

cut diwn and use it for furniture and buildings. We could replace concrete with wood.

It’s a very inefficient (in time, and total carbon captured) way of doing it is the problem.

See

https://en.wikipedia.org/wiki/Biochar

and

https://en.wikipedia.org/wiki/Bioenergy_with_carbon_capture_...

> unless you can bury the plants.

Maybe this is a naive question: but why not bury plants? We got into this mess by digging up long-buried plants, so why not literally reverse the process? With intentional effort, maybe this could be a viable solution? (Probably not -- but I'm curious why.)

No need to. Trees bury about half their biomass as roots. Then leaves and branches fall on the ground and bury older leaves and branches. Of course it's long and inefficient (because of fungus, bugs...) but plants do it without our input so we need to let them do their thing. Calling this process net neutral is a falsehood.

Of course it's not enough to balance human emissions. Sequestering carbon in fields, as pointed out, is a win-win solution which may do a large part in canceling emissions.

https://en.wikipedia.org/wiki/Regenerative_agriculture#Carbo...

Possible. Practical. Increases productivity.

What about building houses and furniture with the wood?

That is typically only sequestering the carbon for 20-50 years. In the end, the house is torn down, or the furniture burned. Very little lasts for more then a century, and basically nothing lasts for more than a millennia.

Deep underground sequestration is the only viable strategy if your goal is total CO2 reduction in the atmosphere.

What if you develop an animal that eats the plants, and then when they die they are buried, such that after the decomposition process all that's left is a fossil? I don't see how that could go wrong unless someone digs up the fossils later on for use as a fuel, but that seems like such a ridiculous an unlikely scenario ha ha ha!

When the animal eats the carbon (as a food source), it combines the carbon with oxygen and exhales...

Or the animals turn out to be delicious and people start coking them.

One of the things I really like about regenerative agriculture (there are so many things to like) is that it makes eating meat cool again.

> Deep underground sequestration is the only viable strategy if your goal is total CO2 reduction in the atmosphere.

That is untrue. So untrue it seems like a deliberate lie.

The only solution is to stop pumping CO2 in into the atmosphere.

There are mitigations. Building huge machines to sequester relatively small amounts of carbon in underground chambers is probably a mitigation. It seems to me that there are better ways and these sorts of ideas are not worth the opportunity cost.

Even if we stopped burning fossil fuels 100%, we still have too much carbon in the atmosphere no?

Yes but not too much that we can't just wait it out. It's not like the planet is a hot fireball right now. If you wanted to make the planet more hospitable to humans, you would most likely attempt to stop desertification and deforestation rather than attempt CO2 capture. Increased water retention will help with droughts more than a 1°C reduction in global temperatures.

Of course, we are going to see far more than a 1°C increase which is why it is worth doing.

It's not a terrible solution, but you need specific trees of specific thicknesses for it to be possible at all (and these aren't always the same trees best suited for rapid growth). Selecting the most carbon-intensive plants and then turning them into biochar is probably better for long-term sequestration.

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