Comment by yodon
7 hours ago
>Economics rules everything
Physics rules everything, once you start trying to run at scale.
The density of carbon per unit volume in solid materials of interest doesn't vary that much, whether you sink it in trees or in exotic materials like diamonds. That means you can calculate the volume of material required so sink a desired amount of atmospheric carbon.
If you want to have a measurable impact on the atmosphere, say dialing it back to 1980 CO2 levels, you're talking not about making a pile of stuff but about making a mountain range that's a mile high and hundreds of miles long.
Now figure out how many trucks you're going to need to move that much material from where your sequestering machine is to where your pile of stuff is.
Or if you want to dump that material in the ocean (which someone else will certainly object to), extend your calculation to figure out how many container trucks worth of material you need to dump into the ocean every hour to accomplish your atmospheric cleanup in whatever amount of time you choose (a decade? If it takes a century, that's not fast enough).
And finally think about surface to volume ratios. You're trying to sink it into a volume, but you can only get the gas into the volume through its surface, so the speed of your process is limited by surface area.
If you want to do it with trees, my personal spitball estimates are that you probably need to plant somewhere between the entire state of Connecticut and the entire state of Colorado to have the kind of impact one would want (there's more subtlety to tree calculations than one generally likes to admit, so feel free to come in with way higher numbers than I did).
Which brings us back to economics. If you have a well-managed forest of that size and scale, someone is eventually going to come along, maybe in 100 years, maybe in 500 years, and say "hey if we cut this down, we could burn the wood to heat our homes" and all that carbon goes back into the atmosphere, so you actually need to sink it into something that is energetically unfavorable for recovery, which means you also need to expand a huge amount of energy to sink the carbon into that energetically unfavorable state.
If we took all the CO2 out of the atmosphere and converted the C into graphite and spread that uniformly over the top 10 subtropical deserts it would be around 2 cm deep.
This suggests a long term approach of building solar powered carbon capture plants in subtropical deserts, they capture it and convert to graphite, which is then spread out under the solar panels.
I once did the math on this, using the specs for currently available solar powered carbon capture, and it came out to something like if we used 100 years worth of the current production annual production of solar panels for this we could carbon capture at a rate that could drop the atmosphere from current levels of CO2 to pre-industrial levels in a few years even if we do not reduce emission rates.
So...not practical now, but might be feasible as a very long term project that over many decades builds out enough capacity to get things under control as long as we can keep everything from going to hell over that time.
> you're talking not about making a pile of stuff but about making a mountain range that's a mile high and hundreds of miles long.
Just to put it into numbers, wikipedia has the total amount of CO2 on the global warming page, if we assume it's in a 2 kg/l substance it totals to around 180 km^3.
To put it further into numbers -
1). Wikipedia does have a citation [1] saying 2,450 gigatonnes of CO2 have been emitted by human activity, of which 42% stayed in the atmosphere and 34% dissolved in the oceans, with the rest already sequestered by plant growth and land use. As we start to pull CO2 out of the atmosphere, it will begin to be emitted from the oceans as well; therefore, let's assume we have to recapture all excess atmospheric and oceanic CO2:
:: 2450x10^9 tonnes CO2 x .66 fraction to sequester ~= 1.6x10^12 tonnes CO2.
2) Let's convert the CO2 to something more stable for long-term storage: HDPE.
- Convert mass of CO2 to mass of carbon:
:: 1.6x10^12 tonnes CO2 x 12/44 mass fraction of C in CO2 ~= 4.4x10^11 tonnes C
- Convert mass C to mass HDPE; assume HDPE is effectively (CH2)n. Then:
:: 4.4x10^11 tonnes C x 14/12 mass fraction CH2 to C ~= 5.2x10^11 tonnes HDPE
3) That's a lot of plastic! How much volume? Wikipedia says HDPE is ~930-970 kg/m3; let's be conservative again and take the low figure:
:: 5.2x10^11 tonnes HDPE x 1.0/0.930 m3 per tonne HDPE ~= 5.5x10^11 m3 HDPE
4) Those are cubic meters; how about cubic kilometers?
:: 5.5x10^11 m3 x 1.0/1.0x10^9 km3 per m3 ~= 5.5x10^2 km3
In other words, if you turned all the [excess potentially climate-change impacting] CO2 that humanity has emitted since 1850 into plastic (a process that would certainly emit a large additional CO2 fraction given the industrial buildout required) then we'd end up with about 550 cubic kilometers of the stuff. Coincidentally, that's about the volume of Mount Everest according to an intermediate calculation in [2].
So, a mountain of carbon: more than a pile but less than a mountain range.
[1] https://en.wikipedia.org/wiki/Carbon_dioxide_in_the_atmosphe...
[2] https://www.quora.com/What-would-the-estimated-weight-of-Mou...
But if you release the O2 and convert it into diamond, then by my highy-suspect back of the envelope calculations, it'd be a diamond that would fit into one square kilometer, 87 meters high. It would make quite the tourist attraction.
My number is without the O2.
It's a literal mountain chain of plastic. We do have uses for it, but it's a lot.
If we pull this off, I would not expect people 500 years from now to undo it.