Consider these two premises, that both escape your simplified construct, and serve as the constraint to the debate.
C: that throughout the Paleozoic the CO² levels in the atmosphere were more than ten times the levels they are today. (and life thrived!)
D: that 99.5% plus of all known carbon that there is on earth, has since the Paleozoic been 'consumed' by life, now exists as dolomite, limestone & marble. The Carbon "cycle" does not iterate. It is a one way street. When we consume that last 0.5% of Carbon all plant life dies on earth (in about 50 million years).
Now to me the outcome of D: does seem catastrophic. But a true scientist would tell me for sure.
Catastrophic, unless we can get substantial CO² back into the system, and hence too, the atmosphere.
