how would carbon dioxide composition change if the movement of continental plates ceased?

Answer 1

I don't think anybody knows. Lots of deposited carbonates on ocean floors are supposed to be subducted and locked up tectonic pplates / continental shelves for 'a long time' before volcanic action releases them again. If the plates stopped moving then the amount of water subducted would drop dramatically; would this lead to a reduction in vulcanism? Even if it didn't reduce the vulcanism it ought to reduce the amount of CO2 and water vapour released - What would happen to the carbonates lying on the sea bed that aren't being sucked back into the mantle?

If anyone has any links to quantitative estimates of what is going on at the moment I would be interested too - thanks for posting this question.

Answer 2

You wouldn't have volcanoes which produce lots of CO2

Eventually, without earth movement soil quality would decrease which might reduce plant life and increase CO2 (but that would be over many 1000s years)