There was a rapid growth of CO2 that started around 200 years ago[1]. To get a time with the same levels as today, we have to go back 14 million years[2]. Back then the species alive were different than the species alive today, with one notable difference being humans. I don't think it's safe to assume we can take the CO2 levels back tens or hundreds of millions of years and assume the species alive today will handle that well.

>I suspect the answer 200 because it is assumed these days that CO2 produced since 1800 is all man made. Would like to genuinely know if that's the case or I'm missing something.

I came up with the number 200 because that's when the graph looked like it started going up. I definitely think it was caused by humans, but I didn't pick the number 200 based on some human historical event, but rather just by looking at the graph. Regardless of whether it was caused by humans, I think such a giant increase is disturbing and should be carefully analyzed for potential problems and dealt with if there are any. AFAIK, there was no CO2 increase as steep as this in history even going back hundreds of millions of years.

[1] https://www.co2levels.org/

[2] https://en.wikipedia.org/wiki/Carbon_dioxide_in_Earth%27s_at...