This confuses the 3-5 year short "residence time" of carbon in the atmosphere with the roughly 50 year "adjustment time" for added CO2.

It's the adjustment time, not the residence time, which determines the duration of effect of additions of CO2 to the atmosphere.

The four(!) different "lifetimes" of added CO2 are explained here:

Burton, D.A. (2024). "Comment on Stallinga, P. (2023), Residence Time vs. Adjustment Time of Carbon Dioxide in the Atmosphere." OSF Preprints. https://doi.org/10.31219/osf.io/brdq9 (and supplemental material here https://sealevel.info/Comment-on-Stallinga2023/)

When a CO2 molecule is absorbed by a puddle or raindrop, that's the end of its "residence time." When that puddle or raindrop evaporates, releasing the dissolved CO2 molecule back into the air, that's the start of a new "residence time." But, of course, the amount of CO2 in the atmosphere is unaffected when a CO2 molecule temporarily leaves the atmosphere, and then returns to it.

Similarly, if a carbon atom is exchanged between the air and the terrestrial biosphere or ocean, either immediately or perhaps after a growing season, that exchange "resets the timer" if you're counting "residence times" of carbon atoms, but it does so without affecting the amount of CO2 in the air.

This confuses the 3-5 year short "residence time" of carbon in the atmosphere with the roughly 50 year "adjustment time" for added CO2.

It's the adjustment time, not the residence time, which determines the duration of effect of additions of CO2 to the atmosphere.

The four(!) different "lifetimes" of added CO2 are explained here:

Burton, D.A. (2024). "Comment on Stallinga, P. (2023), Residence Time vs. Adjustment Time of Carbon Dioxide in the Atmosphere." OSF Preprints. https://doi.org/10.31219/osf.io/brdq9 (and supplemental material here https://sealevel.info/Comment-on-Stallinga2023/)

When a CO2 molecule is absorbed by a puddle or raindrop, that's the end of its "residence time." When that puddle or raindrop evaporates, releasing the dissolved CO2 molecule back into the air, that's the start of a new "residence time." But, of course, the amount of CO2 in the atmosphere is unaffected when a CO2 molecule temporarily leaves the atmosphere, and then returns to it.

Similarly, if a carbon atom is exchanged between the air and the terrestrial biosphere or ocean, either immediately or perhaps after a growing season, that exchange "resets the timer" if you're counting "residence times" of carbon atoms, but it does so without affecting the amount of CO2 in the air.