Yes, Carbon sequestering and storage underground is something that brings out all the usual tin-foil hatters from Greenpeace to the alt-right who fantasize about "gassing the population".
What I am wondering is why we are not planting billions of trees, harvest them, make charcoal and stuff it underground. Or grow algae on roofs and use them to harvest carbon.
I would love to have a good clean home biochar solution to increase the carbon content of the soil of my farm. Something I can stuff prunings and grass and brush cuttings and leaves into, flip a switch, and get carbon out of.
But right now it's mostly DIY solutions that look of varying quality and still generate some smoke.
Wouldn't it be great if every suburban neighbourhood had an efficient pyrolysis chamber that processed the organic waste from the surrounding area?
You use plants to concentrate carbon. You make biochar. And then you put it back in the soil, so you're not depleting it of nitrogen, phosphates, and minerals.
The waste heat that you get from making the biochar is useful energy -- solar energy, really -- that you can use to heat homes, make hot water, and run heat engines.
Maybe even the Haber process too?
The chief challenge I see is how to reduce human labor requirements without increasing capital requirements too much.
I'm also a little concerned about eventually diluting the soil with too much biochar. Because you're sucking carbon out of the atmosphere, but the amount of phosphates and such is remaining constant.
The solution space is large. Lots to work on.
Aside from growing then burying cellulose or cooking it off into carbon, you could also pyrolize it into a liquid form via a self-feeding process if your preferred form of sequestration is to pump it back underground i.e. into previous extraction fields.
Direct air capture is something that makes me doubly wary - Aside from the carbon-density-in-air issue, return-on-energy-invested is a key metric I don't see enough emerging encouraging information about. Incorporating the acres of wind, solar, or hydro required to power a DAC solution, the usual land-use objection to a forestry-based carbon removal approach would seem to evaporate pretty quick.
for (int i = 0; i<= 100000000; i++) { Tree t = new Tree(); t.plant(); }
You need specific types of trees for specific microclimates, otherwise they won't thrive and might die. You need a healthy species mixture, otherwise you are creating monocultures vulnerable to mass pest infestation. You need the right amount of rain. You should not reforest good arable land, because we are almost 8 billion now and everyone wants to eat.
Israelis are very good at reforestation, but it took them over 100 years to recreate some modest forests there.
As far as pure sequestration goes, fast growing plants like hemp are better candidates.
Make charcoal. Use the waste heat. Put the charcoal back in the soil, so you're not depleting it of phosphates, minerals, or nitrogen. Repeat.
Maybe you can even use the waste heat to run the Haber process.