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Comment by MChristopherson | Hacker News Reader

That is an important point that struck home with me when I came to realize just how minuscule the amount of carbon dioxide is in the air relative to other gases: it's nigh-on a rounding error.

I think many of us just haven't internalized the percentages of gasses, and probably, like myself, often have it all backwards. An alien doing a fly-through of our solar system would describe our planet as a nitrogen atmosphere.

In descending order:

  Nitrogen: 78 percent
  Oxygen: 21 percent
  Argon: .9 percent
  CO2: a measly 0.04 percent

Groking that last value really helps frame the challenges that CCS has to deal with (and also gives one an appreciation of just how powerful of a greenhouse gas CO2 is).

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> and also gives one an appreciation of just how powerful of a greenhouse gas CO2 is

It should also be noted that the total atmosphere (dry + water) is about 3% water vapor by weight and H2O makes up the majority of the greenhouse effect.

CO2 isn't a problem because it's the biggest greenhouse gas, it's a problem because it's the one (the biggest anthroprogenic one) pushing us over the equilibrium where net warming is zero.

>It should also be noted that the total atmosphere (dry + water) is about 3% water vapor by weight and H2O makes up the majority of the greenhouse effect.

This is actually an incredibly important point, because higher temperatures mean more water vapor in the atmosphere. However, that also means more clouds, which counteracts warming to some degree.

The impact of clouds on climate change is one of the biggest difficulties in modeling climate change. The IPCC report goes into it a bit. My understanding is that computationally it's a bit like predicting the weather into the future - a lot of uncertainty due to the chaotic nature of the system.

AFAIK one of the biggest problem in numeric simulations is critical phenomena, where depending on a tiny difference in current state, something either happens or doesn't happen. Critical phenomena include phase changes such as water freezing or condensing (clouds). Obviously that's a problem for weather forecasts.

For a long-term climate model, it might work to average out (over space and time) some critical phenomema and assume a steady function from e.g. average air temperature to ice cap size and cloud cover.

(source: wrote some homework-grade numerical simulations, physics major.)

As a handwavy intuition pump, water expands 1,000 times when it boils and turns to steam. Boil 1 litre of water, get 1,000 litres of steam. To go backwards here means sucking in 1,000 litres of pure steam and paying the cost of chilling it to condense it and get 1 litre of water back out. After that, air is not pure steam, it's about 4% water vapour, or 25x less concentrated. To go from air to water means sucking in 25,000 litres of air, and paying the cost of chilling it, to have enough air going through to contain 1,000 litres of water vapour, to get 1 litre of liquid water back out.

Carbon is not 4% of the air, it's 0.04%, a thousand times less concentrated again. To get "1 litre of carbon solid"[1] out means sucking in and paying the cost of processing 2,500,000 litres of air.

[1] as if that means anything sensible here, lol.

I don’t think this is a relevant point. It is after all used for photosynthesis despite the low concentration. The low concentration is an advantage in one way, because you have to remove a relatively small amount.

The low concentration means CCS will be slow. However, we can’t drop CO2 to pre-industrial levels in a week, that would probably cause significant climate instability. The logical thing to do would be to drop the levels at around the same rate as we have increased them. That may be too slow to prevent significant climate change in the meantime. Perhaps the rate could be adapted to how bad things seem.

Nitpicking, but it's 0.04%, sadly.

Thanks for the correction! Fixed.

dumb question but like, 100 years, was it 0.03% and little by little it has crept up to 0.04% due to "humanity" lately?

It's not a dumb question. You're right. It was just below 300ppm a century ago, and it's a bit over 410ppm now. https://climate.nasa.gov/news/2915/the-atmosphere-getting-a-... is a good overview.

The NOAA has a station on Mauna Loa in Hawaii. It has been continuously collecting CO2 data since 1958 and CO2 has gone from just over 300ppm to the current 414ppm.

How much carbon capture would it take to get from 414ppm to 300ppm? Or is the new goal to just stay at/around 414ppm and not go backwards?

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