Comment by tzs | Hacker News Reader

Comment by tzs | Hacker News Reader

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> Every Gigaton of carbon is roughly equivalent to covering the entirety of Texas in ~3 feet of carbon

That seems high. I get a lot smaller number, but maybe I've messed up some unit conversions. I'm using:

  1 ton = 10^3 kg
  1 g CO2 = 12/44 g of C (C == carbon, not Celsius)
  Density of C is 2.2 g/cm^3
  1 Texas = 6.95x10^5 km^2

Assuming those are right and I didn't botch any conversions between metric prefixes I get this:

  10^9 tons CO2 x 10^3 kg/ton x 10^3 g/kg = 10^15 g CO2
  10^15 g CO2 x 12/44 g C/g CO2 = 2.7x10^14 g C
  2.7x10^14 g C x 1 cm^3 C/2.2 g C = 1.2x10^14 cm^3 C

  6.9x10^5 km^2/Texas x 10^10 cm^2/km^2 = 6.9x10^15 cm^2/Texas
  
  1.2x10^14 cm^3 C / (6.9x10^15 cm^2/Texas) = 1.7x10^-2 Texas cm C

Check:

  1.7x10^-2 Texas cm C x 1 km / 10^5 cm = 1.7x10^-7 Texas km C
  1.7x10^-7 Texas km C x 6.9x10^5 km^2/Texas = 1.2x10^-1 km^3 C
  1.17x10^-1 km^3 C x 10^15 cm^3/km^3 x 2.2 gm C/cm^3 C = 2.57x10^14 gm C
  2.57 gm C x 44 gm CO2/12 gm c x 1 ton/10^6 gm = 9.4 x 10^8 ton CO2 = 0.9 gigaton CO2

PS: the above is for 1 gigaton of CO2 since that is what emissions figures usually use. But if you were just talking about after capture and extraction of carbon, multiply the above by 44/12, giving 6.2x10^-2 Texas cm C.

PPS: If we took all of the CO2 out of the atmosphere, the amount of carbon would be enough to cover to Texas to about 53 cm.

Thanks - updated.

Not as ridiculous - but still not a solution.

I don't think storage for the captures carbon is really a limit. I think the main limit would be the materials to construct enough carbon capture facilities to do the job.

One nice thing about carbon capture is it doesn't matter much where you do it. The atmosphere does a great job of spreading CO2 nearly uniformly. You just need places with sufficient available energy and somewhere to put the carbon.

One possibility would be subtropical deserts. They have plenty of sunlight for energy and plenty of land that could be used without displacing many people.

Imagine carbon capture facilities that consist of a solar farm for power with the panels mounted a few meters off the ground, and we dump the captured carbon under the panels.

As calculated earlier, 1 gigaton of captured CO2 would give enough carbon to cover Texas to a depth of 0.017 cm. There are about 3000 gigatons of CO2 in the atmosphere, so if we captured all of it, that would cover Texas to a depth of 51 cm.

The 5 largest subtropical deserts have a combined area 22 times as big as Texas. If we covered just 10% of that area in solar farms to power carbon capture with a meter of room under the solar panels we'd have plenty of storage space.

At the efficiency of current solar farms and current carbon capture, they would be capturing about 10% more carbon per year than we are currently emitting. Cover 90% of those 5 deserts with such plants and in under a decade we could get back to preindustrial CO2 levels.

The big limit that I see on doing this is production of solar panels. At current production rates, covering 10% of the 5 largest subtropical deserts would use about 180 years worth of solar panels.

I have no idea if there are enough raw materials available to let us to increase that enough to make it worth considering.

> The big limit that I see on doing this is production of solar panels. At current production rates, covering 10% of the 5 largest subtropical deserts would use about 180 years worth of solar panels.

Yes, that is the problem. It is pie in the sky to believe that's happening any time soon. It would take >20 years before it's making any meaningful dent in emissions.

We're going to keep emitting CO2 at current rates for close to a decade before they really start to drop. You're looking at ~1/3rd of the earth being covered in solar panels and ~15 feet of carbon. Maybe I'm naive. I just can't imagine it.

You think we're going to do that and we can't even build nuclear power plants? That would've mostly solved the problem before it even happened.

And I imagine that would have cost 10,000x less.

> I have no idea if there are enough raw materials available to let us to increase that enough to make it worth considering.

I don't know enough about the materials used for CC, but for solar panels - raw elements is not a problem if you're planning to use 90% of subtropical deserts...

> Imagine [...] solar panels mounted a few meters off the ground, dump the carbon under the panels.

When I try to imagine that, I can't help it. I see leaves mounted on top of a tree. Using solar power to bind carbon into a dense trunk package below. Ready to be carted off and hidden below grounds.

Also, given that we can't find anyone willing to pay for carbon capturing right where it is most dense, at the source, how are we going to find the will to pay for capturing it from thin air at much higher cost...

Imagine wind/solar power plants that pump water into present day deserts in volumes great enough to turn them into rain forests. How much carbon would that bind?

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