you misread the article
It's about the lifetime of the extra CO2 pulse, not the lifetime of each individual CO2 molecule. Nobody cares what happens to individual molecules, but rather if there will still be elevated CO2 readings centuries/millenia in the future due to human emissions. Saying otherwise is missing a rather dramatic point.
His H2O comparison showed an alteration in the amount quickly returned to equilibrium - again, about a change in the amount, not the lifetime of individual molecules.