A ton of corn costs about $166, let's say that's half carbon. So each gigaton will cost about $300 billion, and thats just to buy the corn, not including the digging, etc.

You'd need to collect about 900 gigatons to return the atmosphere to preindustrial CO2 levels.

The cost of corn stover (leaves and stalk) is $40-$80 including transportation it's about $100 per ton [1].

So, that's $90 trillion at US biomass production prices (assuming that much biomass was available) or 1.2x world annual gross world product [2].

Still $90 trillion seems like a lot.

[1] https://www.extension.purdue.edu/extmedia/EC/RE-3-W.pdf [2] https://en.wikipedia.org/wiki/Gross_world_product

It's a far better idea to dump the carbon in after it has been used for it's energy and is bound up in a more stable configuration, ie biochar (a.k.a. terra preta or low temp charcoal). Biochar is stable in the soil for thousands of years, and provides a matrix on which soil organisms can thrive. There are also some indications that the biochar induces greater plant growth because the residual bio-oils and aromatic hydrocarbons cause the plants to think that there was a recent fire and this is there opportunity to take over.

But more importantly, and to your point, it is a carbon sink, and if made through gasification produces a carbon negative energy source.

Biochar is also alkaline. Why not dump it in the sea? Then we get a two-fer: capturing carbon and de-acidifying the ocean.

Plenty of empty tankers leaving US shores, I'm sure the captains wouldn't mind having a heavier ship, and it shouldn't hurt the fuel efficiency much at all. But, mechanically, how to empty it into the sea? Put conveyers on deck and dump it over the side as you go?

Or pump it in and out as a slurry. That's typically the most convenient way to handle granular solids.

I ran numbers on energy equivalence of fossil fuels to wood in a recent comment. Very roughly, a ton of coal or barrel of oil equals a cord of wood (actually somewhat more, but close enough).

Given US timber production and multiplying by five to get an estimate of global timber ... estimated fossil fuel resources are equal to about 200,000 years of global timber production.

That's a lot of wood.

Even if you're only looking at a small recoverable portion, say 10%, it's 20,000 years.

Energy translates reasonably well to carbon. There's some allowance for natural carbon sinks. But truth is we're messing with the carbon cycle in a huge way.

Because the rotting process would create methane which would seep out easily, its wasteful and ethically questionable (people are still starving, so not even using corn as fuel is pretty horrible). Storing Carbon cheaply and safely is to me an unsolved problem. Especially if you want to do it without wasting tons of minerals (before someone talks about vacuumed dried algae or stuff like that).

I like the idea of building stuff out of wood. Then we can have nice buildings and store carbon.

There's actually a really good idea in there.

After transport, building materials are a large energy consumer. Coming up with alternatives to concrete, steel, aluminium, and similar materials, possibly though biologics, whether low-tech like wood, or self-forming biocrete and biobrick.

Paving, especially.

People are working on it eg. http://woodforgood.com/sustainability/build-with-carbon

and a TED talk https://www.ted.com/talks/michael_green_why_we_should_build_...

I'm aware of that (and pointed to a few examples myself).

What I'm pointing out is that energy is a means to some service goal, and in the case of construction, alternate means to ends may well obviate much the need for new energy supplies.

Or taking an alternate formulation: rather than tap energy and convert and store and transform it multiple times to accomplish some goal, employ biological means to achieve the same end with far fewer (loss-entailing) energy transforms.

Trees, plants, algae, and/or microbes, operating over a large area, accomplish a very large net throughput. The questions are whether we can manage that, what outputs are possible, at what rates, and what subsequent changes in capabilities result. I suspect no biologic will have, say, the capabilities of steel. If we're limited to masonry or ceramic-based structures, the age of the 100-storey supertower is gone, but there are a many 10-20 storey towers which might be possible, resulting in high urban densities, if that's what we want.

What about Iron fertilization of the upper ocean to stimulate a phytoplankton bloom?

You're half right on the wasteful and ethically questionable part: corn is very low nutrition, and is basically junk food. Growing it at all while people are still starving is pretty horrible.

There are actually proposals to do something like that, however it's more likely to be wood, not corn.

But this has all kinds of potential issues. The likely biggest one is that whatever you want to bury needs to be grown somewhere. It needs space where things can grow, that means space and soil that can't be used otherwise to grow food. If you cut down existing trees you're likely causing more emissions than you bury. If you create even stronger competition around fertile land you also create more carbon emissions through indirect landuse changes.

So yes, this is a potential option, but it needs to be carefully weighted against potential downsides.

Fresh Kills landfill could hold about 3 gigatons of biochar at 1.5 g/cm3, assuming an average depth is 100 m. So we need 300 of those.

There are some deep canyons in the Rockies where there are very high bridges and little meaningful waterway below. I'll bet you could fit a lot more than 1 Fresh Kills in some of them.

Coal trains run those tracks. American coal cars empty from the bottom. When the coal trains are empty in Wisconsin, Chicago, etc, they have to go back to the mines anyway. They can dump the biochar in a ravine en route. just need to remove a few ties and install the coal emptier.

Wood or coal, the corn trains and timber trains deliver to similar places. Build biomass energy facilities in those rail transportation hubs. Omaha, Kansas City, Fargo, the Twin Cities.

Of course it would make more sense to just leave the coal in the ground. But humans don't do well with static equilibrium.

And you can add it to the food price: this hamburger was made from stover-fed beef. And twice the animal's feedstock in biomass was burned in biomass plants, and the biochar was sequestered.

Omaha Steaks could sell 2x, 3x, 4x, and 10x beef.

It'll raise the price of beef.

I wonder which picks up mass faster, corn or some of the more virile species of weed tree.

To an extent, that actually works to sequester carbon, but it's not clear that it's the most cost-effective way to do it. Nor would people be OK with the perceived waste.

Just use the stover. And slaughterhouse cities like Omaha and Kansas City and Chicago also import their fuel and receive timber.

Let's take Omaha. Omaha Steaks could sell carbon-negative beef if the USDA inspectors can certify that 2x the carbon went into biomass energy plants. It would create demand for 3x, 4x, and 10x beef.

I'm curious, what would be the most effective way to sequester carbon?

Possibly shellfish, given past limestone deposites (calcium carbonate).

It turns out people start dying when you dump the only food they can afford into a hole. We tried that with ethanol subsidies.