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Comment by rossdavidh | Hacker News Reader

I would need to see something about how much electricity they're talking about here. I am not seeing a way to do this with less than the electricity you got from burning the fossil fuels in the first place (and inevitably, somewhat more). The only way I could see this being useful is if at some point in the future we are no longer burning fossil fuels for electricity, and we want to get the CO2 back out of the atmosphere. But, you know, turning them into living trees is not a bad way to do that, and it already exists...

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You're mostly right, except that trees are now understood to not be a great way to sequester carbon: They eventually grow old and die, and the carbon in them is released as they rot. Over (non-geological) time trees are net carbon neutral.

I hear that mentioned a lot. But there are some important considerations. Taking previously unforrested land and converting it to forests will sequester carbon for as long as that condition holds. Planting trees and either letting them grow into old growth forests or using them for lumber can sequester carbon for centuries. Don't underestimate the value of buying time to transition to clean energy and develop more advanced technology.

That’s my thinking as well. This problem arose on the human timeline. It must also be solved on the human timeline. The real requirement is th carbon being out of th it within the human timeline and that the sequester process be continued. Seems like a net boon to the economy that way.

I know I’d love to see homes built out of wood more often, as well.

Many tree species live for thousands of years, most for hundreds. Growing them will sequester a lot of carbon. Plus the soils in mature forest will sequester more. The amount of carbon you could sequester in a mature redwood, or fir forest is huge. In climates where these tree wont grow, oaks often will and can capture a lot of carbon and live for millennia. I would be interested on where you got the idea that trees are not a good way to sequester carbon (ref to a paper?).

Not even over geological timescales anymore: from what I picked up in discussions (I'm not an expert), the majority fossil carbon was trapped at a time when trees had a defensive "technology advantage" over fungi so big that they would resist all rotting even after death because nothing the capability to "digest" wood had not been evolved yet. That way they could just accumulate until getting buried by those incredibly slow geological processes.

The key is to turn the trees into biochar and put it back into the soil.

This is where this idea seems viable. As a national project, why not plant some fast growing trees in some sizable plot of land. Once they reach a maturity optimum cut them and lay them underground? It has the potential to pull co2 out and put back oxygen.

You can't just bury trees whole, you need to convert the cellulose and lignin into charcoal so the microbes in the soil can't break down the carbon (coverting wood to charcoal basically scrambles the carbon bond structure preventing the easy enzymatic cleavage of the cellulose polymers).

A few people have suggested doing exactly this with nitrogen fixing trees like Casuarina sp.

I’m not sold on having to make them charcoal. My thinking is they are essentially rejoining a natural cycle at that point. And probably a portion may be sold for consumer products. The carbon needs to be out of the air, yes. But it doesn’t have to be locked underground to be out of the air.

If facilities for this process can use "waste" electricity (e.g. more solar than is being consumed on the grid and/or off-peak surplus electricity from other sources), then it makes economic sense.

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