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.
> 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.
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.
… 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.
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.
This may be one of our best options, and we should accelerate more research in that area.
[0] https://en.wikipedia.org/wiki/Biochar