Source here. In order for increased human CO2 emissions to cause accelerated global warming, the climate models need to assume that CO2 remains in the atmosphere for a very long time, up to 100 to 200+ years. (click on image to enlarge)
Since the IPCC's task is to prove any global warming is due to human CO2 emissions, they decided to proclaim that CO2 was long-lived in the atmosphere - a fabricated assumption.
They did this despite the overwhelming majority of peer-reviewed studies (see chart) finding that CO2 in the atmosphere remained there a short time.
Literally, a fabricated assumption, driven by political agenda, became a cornerstone of fraudulent climate model science. As a result, billions spent on climate models that are unable to predict climate with any accuracy.