Then there are all the physical processes involved in CO2 transfers between the atmosphere and soil and between the atmosphere and oceans. There are hundreds of assumptions in these models and if just one key assumption is substantially in error, then all the forecasts produced by the model can be totally wrong. That’s what has happened with the IPCC’s model, except that model has numerous errors.
I’m sure the CO2 modeling is quite poor. But that doesn’t really change the fact that the CO2 increases are primarily fossil fuels, not outgassing. But plant uptake and sequestration in soil is not modeled well, however it is fair to say that those physical processes change slowly compared to the current rise in CO2.