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Comment by silverquiet | Hacker News Reader

I'd be curious to see the science on enhanced plant growth; my understanding is that the benefits of increased CO2 fade very quickly. I believe we can already see plant pores evolving to be smaller as they were in previous times when the Earth had greater CO2 levels.

About the only thing that gives me hope is SRM, but it's a half-assed solution at best. A world with 800ppm CO2 and a dimmed sun via aerosols is not the Earth that I was born to; it is probably not possible to fully understand the affects.

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The optimal CO2 level for plant growth is between 800 and 1000 ppm, as observed within greenhouses.

https://www.frontiersin.org/journals/plant-science/articles/...

There is no perfect solution. One of the benefits of stratospheric aerosols is that they only stay suspended for 10 years or so, reducing the risk of long term effects. They are also an exceptionally cheap strategy, on the order of a few billion a year to cool the entire Earth. Compare that with the many trillions needed to just get to carbon neutral, while significantly reducing economic growth and living standards.

The world we were born into will not exist in any scenario. As they saying goes, you never step in the same river twice. CO2 emissions show no sign of decreasing, especially as China, India and Africa continue developing. Furthermore, we are on the cusp of AGI within the next decade or so, which will radically change reality far more than the Earth possibly getting a bit warmer in a 100 years or so. The IPCC does not even predict major cataclysm, and expects only sea level rise of a couple feet in the worst case scenario.

> they only stay suspended for 10 years or so

And then what happens? Earnest question.

Back to the ground in rainfall I guess.

Yeah that's kind of what I was getting at: the implications of all these aerosols falling to earth later, and getting into everything.

Calcium carbonate aerosols are proposed as a good alternative to sulfur dioxide since they are basic and do not react with ozone. Calcium carbonate is used an additive to soils to reduce acidity and is used by organisms to construct bone tissues. Furthermore, these aerosols would be extremely diffuse. It's estimated that we'd need 5 million tons of sulfur dioxide per year to reduce temperatures by 1 degree centrigrade. Assuming we need 10 million tons of calcium carbonate that eventually descends to the Earth, that would come out to be 0.0196g per square meter. Effectively negligible, and may even be beneficial for areas that have slightly acidic rains.

And then we have to do it again, and again, and again; once you grab that tiger's tail, there is no letting go. In the meantime, sense of urgency abated, we would most likely keep on burning fossil fuels and putting more CO2 into the atmosphere, locking ourselves further into the loop.

It is a terrible idea which will almost certainly happen.

Entropy is inexorable and must always be resisted. Humans need to drink water and eat food, again, and again, and again. Unimaginable amounts of time, effort, and resources are spent every day maintaining civilization. If we build out solar panels, we will have to replace them in 20 years. There is no free lunch.

We don't know how bad the climate will be at 800 ppm. 300 millions years ago, during the Carboniferous era, there were vast forests and very high CO2 levels, around 1000 to 5000 ppm. If the Earth gets too hot we will simply do stratospheric aerosol injection. If climate change turns out to be overhyped, then we get the CO2 fertilization boost for free, win-win.

Regardless, the real solution is next level energy production from advanced fission, deep geothermal, and ultimately fusion power. With a vast surplus of energy we could do wildly impractical things like filter sea water for gold, and of course extract extremely diffuse gases from the atmosphere. Renewable energies are very low energy density, and more akin to farming from a physics perspective. They make sense in certain situations, but are not reliable for powering an advanced industrial civilization.

I also suspect people's intuitions are out of perspective in terms of time scales. It seems likely AGI will arise within the next 20 years. Climate change is nothing compared to the singularity and rise of superintelligence.

Seems plausible at least, and you are of course correct about the world; the CO2 level of the atmosphere when I was born was well below 400 and we'll not see that again as long as I live. That's what I tell those who respond viscerally to the idea of messing about with the atmosphere purposefully - we are already altering it regardless.

I mean, we can try to un-alter it rather than altering it further and hoping it will cancel out.

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