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Comment by danbruc | Hacker News Reader

If I didn't make a mistake, we are looking at removing two trillion metric tons of carbon dioxide per ppm. That is probably not a small feat.

EDIT: Of course I made a mistake, it is probably more like three trillion metric tons, I mixed up fractions of volume and mass.

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Don't forget that you'd have to do that in an entirely carbon free way and cease all current carbon emissions. That's not happening in our lifetimes.

I would use caution throwing around ultimatums. I'm sure pocket-sized digital supercomputers or a global near-instant communications network didn't seem likely within the lifetime of people born in the Great Depression, but here we are.

These exponential advances in technology are difficult to predict with human brains. I try to stay cautiously optimistic.

This of course depends on the time frame one wants to achieve, but assuming we want to remove carbon dioxide as quickly as we added it, that means we would need some operation comparable in size to the global coal, oil and gas industry extracting carbon dioxide from the atmosphere around the clock. And while I agree with you, exponential growth is in some sense hard to predict, I don't really see us starting such a gigantic endeavor unless we are absolutely forced to by the consequences of climate change.

You make solar power cheaper than coal, and atmospheric carbon useful for something, and you'll soon have to regulate it extraction, not emission.

Today's computers were perfectly obvious to Gordon Moore in his 1965 paper. By contrast nobody today is writing papers about the inevitable expansion of carbon-free energy production.

Some folks are certainly hinting at it. http://rameznaam.com/2015/08/10/how-cheap-can-solar-get-very...

Various forms of next generation nuclear would meet that requirement right? People are certainly writing papers on building better nuclear power plants. Doesn't even have to be something exotic like fusion.

If there is some kind of nuclear power that is millions of times cheaper per unit output than it was in 1965, I am unaware of it.

> Don't forget that you'd have to do that in an entirely carbon free way and cease all current carbon emissions

Plenty of carbon is naturally removed from the environment, at least partly by photosynthesis; that's how an equilibrium was maintained before we humans in wealthy countries started releasing so much more carbon into the atmosphere. We don't need zero emissions.

Carbon is generally not removed from the environment by photosynthesis.

In photosynthesis, CO2 is converted into sugar [0], storing the solar energy in the chemical bonds of the sugar molecule. Later, the energy is released through the reverse reaction where the sugar is converted back into CO2 [1].

Carbon is also used in biology for things other than sugar production, but in general the carbon that gets consumed by an organism eventually gets released when that organism (and the organism that ate it, and so on up the food chain) decays. This is refered to as the carbon cycle.

Under some circumstances, the carbon cycle is broken, and dead organisms end up sequestering their carbon in a place that does not allow it to return to the general environment (eg. fossil fuels).

TL;RD when we burn fossil fuels we are adding carbon to the environment. When plants consume carbon, they are moving it from the atmosphere to another part of the environment, and it almost always ends up back in the atmosphere.

[0] The full reaction is CO2 + Water -> Sugar + Oxygen, or 6(CO2) + 6(H2O) -> C6H12O6 + 6(O2)

Yes, good point. I knew that but somehow it escaped me when I wrote the post. My point was, the global ecosystem can handle the release of some carbon by human activity without a problem; we don't need to go to zero.

However, the sooner and farther we reduce carbon output, the faster we reduce excess carbon in the atmosphere. There's nothing magic about zero; negative output would help too.

until Elon Musk does something about it. Right ?

Plants are able to remove about 10ppm per year. If we stopped emitting, and starting burying plants in the ground it could be done without a huge problem.

i.e. the hard part is not removing the CO2, the hard part is not adding to it.

Trying to bury a significant portion of the global plant mass gain every year in a way that it does not emit greenhouse gases while decomposing seems like a major undertaking to me.

A quick calculation - one ppm reduction means extracting three trillion metric tons of carbon dioxide which contains about 800 billion tons of pure carbon which takes up about 400 cubic kilometers. That is a huge hole to dig even if we would just have to deal with the carbon. And that is for one ppm.

> three trillion metric tons of carbon dioxide

Billion not trillion (10^9). All the rest of your numbers are off by a similar factor.

> That is a huge hole to dig

Actually, using the correct numbers (.4 cubic km), if you made a 50 foot deep hole it would be about 3 miles by 3 miles. Not that big - a couple of city blocks.

A typical landfill is larger than that, and we have tons of those.

Nope, trillions. The mass of the atmosphere is about 5.15 × 10¹⁸ kg [1], 400 ppm of that are 2.06 x 10¹⁵ kg or 2.06 x 10¹² t which are about two trillion (short scale) or two billion (long scale) metric tons. I used the short scale [2]. And because the 400 pm are by volume and not by mass you end up with about three trillion metric tons if you take that into account, too. Of course only unless I messed things up.

[1] https://en.wikipedia.org/wiki/Atmosphere_of_Earth

[2] https://en.wikipedia.org/wiki/Long_and_short_scales

Your figure is for 400ppm. But we are talking about 1ppm.

Of course, sometimes you are just blind for the error.

Don't we have plenty of old coal mines? They seem like a natural place to sequester carbon in, given that that's where a lot of it came from in the first place...

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