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Comment by teslabox | Hacker News Reader

The percent change is relatively small: 0.028% (280ppm) of the atmosphere to 0.0425% (425 ppm). Even if atmospheric CO2 doubles from today's level, it won't even be 0.1% of the atmosphere. (Edit: "For the majority of greenhouse crops, increasing CO2 levels to 1000 ppm (parts per million) results in an increase in photosynthesis by 50% over ambient CO2 levels." [0])

~25% of CO2 emissions are captured by the oceans. The increased productivity of terrestrial plants captures more of the emissions. I don't think the inertia provided by CO2 captured by the ocean is taken into account. This is presumably why the COVID lockdowns didn't make much difference for atmospheric CO2 levels: https://www.bbc.com/news/science-environment-55018581

The most important of the "complex downstream effects" of increased atmospheric CO2 is increased agricultural productivity.

[0] https://pulsegrow.com/blogs/learn/ideal-co2-levels-and-room-...

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Not sure that is the most important downstream effect. Harvard School of Public Health measured a 15% lower cognitive ability score at 950 ppm and a further 50% decline at 1400 ppm. (https://www.hsph.harvard.edu/healthybuildings/2021/09/09/imp...) So at 1000ppm everyone in the world is just 15% dumber than their baseline ability should be, and 1000ppm atmospheric CO2 will make it much more likely that indoor levels will go up to 1400ppm or even higher unless we start utilizing carbon scrubbing technology for indoor spaces. It's pretty scary to think that modern society could be basically mentally stunted by high CO2, even if crops enjoy it.

I think about this one quite a bit.

The absolute percentage of the atmosphere being what you consider to be a small number is not actually relevant to what the impact of that would be. If I were to give you a pill of cyanide, I don’t know how comforted you’d be by me assuring you that the pill was less than 0.1% of your body mass.

I’m not calling CO2 cyanide, I’m saying “because this sounds like a small absolute percentage to me” is not a salient argument.

This atmospheric gas which makes up a fraction of our atmosphere is responsible for virtually all the organic mass in plant life on the planet, and consequently all animal life. If we agree that [the existence of all biomass on the planet] is not insignificant, then we agree that the small absolute percentage that CO2 represents in the total atmosphere is clearly already sufficient to be highly consequential.

Regarding this point:

> The most important of the "complex downstream effects" of increased atmospheric CO2 is increased agricultural productivity.

You don’t get to decide edgar the most important downstream effect is, not do you make it simple by adding quotes around “complex.” What you’ve referenced here is simply one of the many effects of increasing CO2 in the atmosphere.

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