[dTal]

"carbon based life forms" is a rather broad umbrella, that includes anaerobic bacteria. I don't think you want to be using that as a criterion.

Perhaps we can agree on "the best composition for humans"? In which case I humbly submit the answer is "the one we (and every animal we care about) evolved with".

[bartimus]

Fair enough. So looking at the hundred millions of years of our evolution. What I've been able to gather is that apparently we've had CO2 levels far beyond 1000ppm (0.1%). It's actually been relatively low in "recent times". Plant life pretty much thrives on CO2. Plant life has also been responsible for burying our needed carbon underground.

Is science asking this question? And does science offer a clear answer here?

[ahje]

Are you suggesting that multiple teams of skilled scientists from various parts of the world all forgot to account for historical CO2 levels when they created their models? Really?

CO2 levels has been higher than current levels before, like back in the Triassic. Incidentally, very few humans would like to live in such a climate. It's also worth mentioning that the Triassic was preceeded by one of the worst extinction events that ever affected the planet. An extinction event caused by very high temperatures and increases in CO2 levels.

Sure, life will survive. Probably humans as a species too. The planet won't be the same as now though.

[bartimus]

No not at all. I'm saying the alarming message gets vague beyond "humanity has made a contribution to global warming".

I try to research the available science but have trouble finding clear answers. The most accurate data seems to comes from the ice samples. But that only dates back 800.000 years.

You mention the Triassic period. Co2 levels were 2000ppm during that time. That sounds like a dramatic increase (from 0.04% to 0.2%). But then I also read we already often experience such levels at home or at work. For office workspace 1000ppm is considered acceptable and official limits are set at 5000ppm (as 8-hour TWA). I also read plants will grow ~5 times as fast. More faster reforestation?

We know there will be a change. But how accurately are we able to predict what that change will look like? Is there a strong consensus about it?

[ahje]

CO2 makes water acidic. Acidic water screws with a lot of aquatic organisms. Aquatic organisms create a large amount of the planet's oxygen. Considering the marine ecosystem is extremely sensitive, well, I can see how high CO2 could be a problem even if we humans can still breathe just fine.

[bartimus]

Thanks for this. I wasn't aware the marine ecosystem is so sensitive to changes.