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Comment by mleonhard | Hacker News Reader

Why do you believe that micro-organisms will not break down biochar?

From the article:

> Yes, soil is enormously varied. And it contains a lot of carbon. But there’s no carbon in soil that can’t, in principle, be broken down by microorganisms and released into the atmosphere.

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In principle slowing down the return of carbon back to the cycle is helpful, even if it isn’t a permanent solution. In many ways this is exactly what trees are; a way to convert a ton or so of fast cycle carbon into wood that will retain it for a century or so.

Of course, the numbers matter. I can’t speak to Biochar, since it might not hold onto the carbon long enough.

Biochar is interesting. It seems to be dependent on the temperature your pyrolysis occurs at and likely many other variables. It also encourages microbial growth that can help sustain and even add to the carbon content. There are studies that show it can sequester carbon from dozens to hundreds of years potentially, and patches of "terra preta" found in the Amazon are found to be self regenerating (growing at 1cm/yr) and were originally set down between 450-950BCE. Fascinating stuff.

If biochar is made with 80% or higher fixed carbon it has half life of >500 years in active agricultural soils.

If you have to, you can store it in underground mines.

The result effectively reverse coal mining.

we could skip out the middleman and just leave the carbon in the ground to begin with.

Probably too late for that.

If by "we" you mean everyone, no we can't.

Edit: assuming you know it's too late not to start, propose something other than magic wand obvious solutions.

We could stop all fossil fuel burning today, and we would still need to sequester carbon.

Compared to time travel, carbon sequestration is easy tech.

And you would need nothing less than time travel in order to persuade the mining companies of the 18th-20th century not to mine coal.

Biochar is pyrolyzed lignin, lignin is notoriously difficult to break down

… and while fungi have certainly figured out the lignin thing, pyrolyzed anything is much harder to break. Unlike fresh organic stuff, most of the N, even O and H is gone. It’s just more favorable to eat something else.

The process removes almost everything except the lignin, leaving the same lignin structure - but broken and slightly hydrophobic from the residual creosote.

Pure carbon is already pretty much broken-down, chemically, unlike longer carbon-based molecules.

You can still oxidize carbon, to form CO2, rather than ... probably graphite or similar forms.

Plants themselves don't do much with soil-based carbon. I'm not sure what the microbial activity based on it would be.

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