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Comment by defrost | Hacker News Reader

I'm not suprised, I have a very good idea about the sheer scale of industrial plant building that would be required to make a significant dent in our current consumption and emissions.

The great unspoken catch to direct air capture technology as that develops is while it will (at sufficient scale) mitigate the extraction of "old" carbon from traditional fossil fuel deep earth operations it will likely serve to maintain the cycle of already extracted carbon in the air: (energy + air) -> fuel -> (carbon in air).

Don't get me wrong, these are good steps forward, they're just not solutions unto themselves - we still as a species need to reduce the absolute amount of insulating material in the atmosphere.

Currently we are not.

When we do start to wind back the amount added, we have to keep winding it back by a few hundred billion tonne.

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There's only 7 billion tonnes of carbon dioxide in the atmosphere, total; winding it back a few hundred billion tonnes is not going to be physically possible unless you're talking about Venus. (Which is, admittedly, a pretty appealing prospect.) Here on Earth, the amount we need to remove is 0.02 hundred billion tonnes to get back to pre-industrial levels. That is, 2 billion tonnes. Of CO₂, not carbon.

There are a variety of different possibilities as to what to do with the extracted carbon. CO₂ is kind of an inconvenient form for making fuels from, so as long as they can cook oil and gas out of shale, people might just pump the carbon dioxide down wells and let it serpentinize some olivine, rather than reducing the carbon back out of it.

To one significant figure, the mass of CO2 in Earth's atmosphere is 3 trillion tonnes. Annual fossil fuel emissions of CO2 are about 37 billion tonnes:

https://www.iea.org/reports/co2-emissions-in-2023/executive-...

Hmm, I'll have to figure out how I got that so wrong. That would explain some things that were bothering me about the Portland cement stats I posted yesterday. Thanks for the heads up!

No drama from my PoV - it's easy to get magnitudes etc. wrong and these are large numbers.

I haven't checked against the GeoPhys journals (I should, but ...), FWiW wikipedia has it that:

    In October 2023 the average level of CO2 in Earth's atmosphere, adjusted for seasonal variation, was 422.17 parts per million by volume (ppm).

    Each part per million of CO2 in the atmosphere represents approximately 2.13 gigatonnes of carbon, or 7.82 gigatonnes of CO2.

where gigatonne == (US) billion tonne

~ https://en.wikipedia.org/wiki/Carbon_dioxide_in_Earth%27s_at...

That's total, not just the excess portion added in by human activity and sourced from the bowels of the earth via mining for concentrated old sunlight energy.

Still, despite the fractional ppm composition that's a full atmospheric total of 3,301 billion tonne.

Here in W.Australia we move approx one billion tonne of iron ore from the Pilbara to (mostly) China per year. That takes some effort and energy.

It sure looks like I was somehow using the 7.82 gigatonne number as the total, rather than multiplying it by the necessary 422.

A simple calculation in units(1) shows that your figure is the right order of magnitude:

  You have: 400ppm 4pi earthradius**2 atm / gravity
  You want: trillion tonnes
        * 2.1080571
        / 0.47437046

That's a bit low because the 422 ppm number is by volume, not weight, but that is relatively easy to correct with the molecular masses, assuming ideal gas behavior:

  You have: 422ppm (carbon + 2 oxygen) 4pi earthradius**2 atm / gravity (21% 2 oxygen + 79% 2 nitrogen)
  You want: trillion tonnes                                     
        * 3.3925982
        / 0.29475934

And that's within 3% of the number you give from Wikipedia.

Correction to my sibling comment: we do have to keep winding it back by a few hundred billion tonnes. I had the wrong order of magnitude, and defrost had the right one. See https://news.ycombinator.com/item?id=42439752 for details.

> I had the wrong order of magnitude

Absolutely hilarious. Let's compare notes in twenty years. You are too vested in the cult to be able to accept and comprehend reality.

I've done you the courtesy of extensively fact-checking your comments as well as my own, providing you with a boatload of new information you evidently lacked, and clearly demonstrating that some of your conclusions were based on incorrect information rather than reality. I'd appreciate it very much if you'd return the courtesy by correcting whatever information or reasoning I may have gotten wrong, especially if it's something major like the above. Simply sneering at me doesn't advance my understanding, yours (especially if what you're sneering at is that I know things you don't, as it seems to be), or anyone else's.

It would also do everyone a service if you withdrew your claims that turned out to be wrong, as I did in the comment above and in https://news.ycombinator.com/item?id=42440198. That way they don't have to wade through the intricate details of the argument to figure out which of your claims still stand.

In the end the question is: are you here to figure out what is true? Or are you here to conceal what is true, like Ted Turner? I assumed the former, based on past experience, and asked dang to unflag your original comment as a result, even though it was a bit ranty. But this "hilarious" comment makes me wonder if I was wrong.

Unfortunately I still don't see a response to this.

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