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Comment by palata | Hacker News Reader

> I.e. We can use different energy than the one we got out of the fossil fuels we burned.

We're talking about using more energy than the one we got from the fossil fuels we burned, right? So that means that on top of replacing fossil fuels with renewables, we would need to more than double it in order to remove CO2 from the atmosphere.

This, in itself, is impossible. Already we won't be able to replace fossil fuels entirely, we will just end up with less energy in total. We most certainly won't end up with twice as much.

And that's assuming that we could extract the CO2 from the atmosphere with close to the amount of energy we got by burning it in the first place. Which is wrong. CO2 in the atmosphere is actually very costly to extract in terms of energy.

It's not that it's not easy. It's practically impossible.

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So the neat thing is that this isn't at all true.

The total annual CO2 budget of the earth is tremendous; less than 5% of CO2 emissions each year into the atmosphere are from humans. Volcanism, photosynthesis, and other natural sources outweigh humans by far. In numbers, ballpark 730gigatons from natural sources and about 30gt from humans.

If you look at the amount the CO2 levels increase each year in the atmosphere, you'll find that they net increase by 16gt per year or so.

Implying that if we ceased all human CO2 emissions, the atmospheric levels would start recovering at around half the rate they're currently increasing.

This is an absurd statement. Lets use bank accounts instead of CO2 to point out the absurdity.

Imagine every year a company makes $730,000 in revenue but spends $730,000 on various expenses. Its bank balance doesnt change because the income and expenses cancel out.

Now suppose the company starts receiving an additional $30,000 every year while its expenses stay the same. At the end of each year, its bank balance increases by $30,000.

By your logic, someone could argue: "That extra $30,000 can't be responsible for the growing bank balance because it's less than 5% of the company's total annual cash flow of $760,000."

That's obviously nonsense. The bank balance grows *entirely because of the net imbalance*, not because the extra income is a large fraction of the gross cash flowing through the account.

The carbon cycle works the same way. Natural emissions and natural uptake are both enormous and are approximately in balance. That 730 gigatons of CO2 released by natural sources has a corresponding 730 gigatons of CO2 capture from natural sinks. Its human emissions of CO2 that are the extra deposit that creates an ongoing imbalance, and that's why atmospheric CO2 continues to rise.

Also photosynthesis is not a source of CO2, on the contrary it's one of, if not the biggest carbon sink, reclaiming a significant portion of that 730 gigatons of CO2 released by volcanos and other sources.

> The bank balance grows entirely because of the net imbalance

Yes, this is my whole point. You wrote a long condescending comment accusing me of being a climate denier that fully agrees with me.

My point is that the actual amount of atmospheric increase per year is less than the amount humans put into the atmosphere per year, so 1) obviously humans are responsible for CC, and 2) could stop it at any time by dropping emissions below the amount the atmospheric increase amount.

It's unclear which message you're trying to convey, but your math checks out.

The net CO2 impact of natural processes is -19Gt/yr. Humans add +37G/yr for a net +18Gt. If we stopped everything, you'd expect -19Gt/yr; however, natural sinks like the ocean will start off-gassing, cutting the improvement to about half.

Because of how long this switch will take, most IPCC options need 100 to 1000 Gt of net CO2 removal by the end of the century to limit the temperature increase to 1.5 degrees.

> The net CO2 impact of natural processes is -19Gt/yr. Humans add +37G/yr for a net +18Gt. If we stopped everything, you'd expect -19Gt/yr

That is the message I am.trying to convey.

> So the neat thing is that this isn't at all true.

Then goes ahead explaining something completely different.

You were talking about how it'll be impossible to remove excess CO2 from the atmosphere without burning unreasonable amounts of energy.

I say that's not so. We need only to sufficiently reduce emissions.

> We need only to sufficiently reduce emissions.

Well I agree on that. And even if we cut them to zero, the temperatures will not go down. So the very best we can hope is to keep the temperatures at the current level, and that's assuming that we cut all our emissions.

And the fact remains that we would need unreasonable amounts of energy to extract CO2 from the atmosphere (it was suggested with solar panels and stuff).

I didn't know that if we completely cut emissions, then CO2 would go down (and temperature would not during our lifetime, but they would at least stop rising). But "humans extracting CO2 from the atmosphere to compensate for their emissions" is impossible for the reasons I mentioned.

Very napkin math shows that annual energy consumption from fossil fuels is 500 exajoules. Every day the earth receives 15,000 exajoules in solar energy.

So to cover double the energy consumption of fossil fuels with solar we need to cover 0.2% of the surface in solar. Compare to around 10% covered in farmland.

Again, very back of the envelope math, but in my opinion this does not seem impossible.

This is like saying "of course we can travel at the speed of light. Proof: the light does it, it's possible".

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