Sonic, As discusses in IPCC AR6 The IPCC AR6 refers to “multiple...

Sonic,
As discusses in IPCC AR6
The IPCC AR6 refers to “multiple lifetimes for CO₂” without specifying which ones [32] (p. 302, Table 2.2; p. 1017, Table 7.15).
Apparently, the residence time (and IPCC’s “lifetime” may take any positive real value, if modeled as a stochastic variable, yet it has certain statistics, such as a mean, which IPCC avoids specifying, preferring to report that the values are multiple. It is interesting that the same reports give specific values for other substances. The reasons for this special treatment of CO₂ by IPCC may be inferred from what follows.
3.2. Separate Treatment of CO₂ Depending on Its Origin

The ambiguity is accompanied by inappropriate assumptions and speculations, the weirdest of which is that the behavior of the CO₂ in the atmosphere depends on its origin and that CO₂ emitted by anthropogenic fossil fuel combustion has higher residence time than when naturally emitted. This is clear in the IPCC AR5:
Simulations with climate–carbon cycle models show multi-millennial lifetime of the anthropogenic CO₂ in the atmosphere.
[31] (p. 435)
It is also repeated in IPCC AR6:
This delay between a peak in emissions and a decrease in concentration is a manifestation of the very long lifetime of CO₂ in the atmosphere; part of the CO₂ emitted by humans remains in the atmosphere for centuries to millennia.
[32] (p. 642 FAQ 4.2)
(This weird idea has a long history, as it was thought from the beginning of climate modeling that the fate of anthropogenic CO₂ is different from that of the natural CO₂. For example, Joos et al. )