AAArgh!

I wrote a longish exposition to pdq's second question/comment and it vanished when I tried to preview it.

I'll try again.

I said: "Humans are burning a lot of hydrocarbon fuels that have increased the amount of carbon dioxide in the atmosphere."

PDQ said' Well, 35% of all atmospheric carbon is returned to the Earth each year, so "stuff" produced by factories during the early days of the Industrial Revolution is long gone.

Also, you seem to be a physics/chemistry type. You did not mention that plants take in CO2 and give us back Oxygen is such quantities that the human-sourced CO2 insignificant.'

I think the numbers look like this:
800 billion tonnes (Gt) CO2 in atmosphere
2000 Gt in various biomass sinks
9 Gt added each year, 5 Gt removed by various 'sinks'
61 Gt involved in plant photosynthesis but 60 Gt returned by plant respiration. So 1 Gt acts as a 'sink' (included in 5 Gt above)
carbon cycle diagram

These people reckon that it will take a long time to lower CO2 down to pre-industrial levels
Carbon is forever

But like you say, I'm a physics/chemistry guy so some of this plant science is not my forte!

cheers
KP