Hacker News Reader

Comment by jbotz | Hacker News Reader

There is one way of storing carbon in the soil for the long term: biochar[0]. Biochar is organic matter heated anaerobically (pyrolysis) until it turns into something like charcoal. Biochar is stable for a long time. You can then bury that in the soil... it seems to improve the soil by providing surface area for soil micro-organisms and to store nutrients. This could be done on a very large scale, and pyrolysis can actually be energy positive because you can burn the hydrogen that's released to perform the pyrolysis and still have energy left over.

This may be one of our best options, and we should accelerate more research in that area.

[0] https://en.wikipedia.org/wiki/Biochar

View on HN

The science does not meet the hype.

> Our review shows there are not enough data to draw conclusions about how biochar production and application affect whole-system GHG budgets. Wide-ranging estimates of a key variable, biochar stability in situ, likely result from diverse environmental conditions, feedstocks, and study designs. There are even fewer data about the extent to which biochar stimulates decomposition of soil organic matter or affects non-CO2 GHG emissions. Identifying conditions where biochar amendments yield favorable GHG budgets requires a systematic field research program. Finally, evaluating biochar's suitability as a climate mitigation strategy requires comparing its effects with alternative uses of biomass and considering GHG budgets over both long and short time scales.

From https://journals.plos.org/plosone/article?id=10.1371/journal...

That paper is from 2013. The science has advanced substantially since then.

Several university laboratories are still actively researching biochar and provide snapshots of the current thinking regarding its usefulness:

https://whitmanlab.soils.wisc.edu/faqs/

http://www.css.cornell.edu/faculty/lehmann/research/biochar/...

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.

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.

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.

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.

Probably too late for that.

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.

It doesn't automatically improve all soil, does it? As I recall it increases the pH level, which may or may not benefit the soil in that biome, or for the given use of the soil if you're growing food there.

This is an important point to consider. The agricultural studies I’ve seen typically apply 80% compost and 20% biochar to degraded soils because biochar is alkaline.

It can also be made less alkaline with better, more sophisticated production technologies (i.e., reactors) that minimize ash.

The southern US traditionally has moderately acidic soils. Low soil pH is increasingly a problem in the Midwest as well due to poor agricultural practices.

> still have energy left over

... if it's dry biomass.

Too much humidity might tip that the other way, unless I am doing the math wrong. Looking at CA's forests right now, that might not be a problem :/

Once bootstrapped, the excess energy can go into kiln drying the input for the next batch.

Honestly not too far from the glib “just bury the coal again” solution.

Reply on news.ycombinator.com