Hausfather and Betts show natural feedback emissions with SSP 8.5 can be up to nearly 700 ppm CO2 or about 5,000 Gt CO2, but generally between 100 and 350 ppm CO2 or 780 to 2,700 Gt CO2. See figure, “Change in CO2 concentration when including carbon-cycle feedback uncertainties.”
Hausefather and Betts, How ‘carbon-cycle feedbacks’ could make global warming worse, Carbon Brief, 14 April 2020.
https://www.carbonbrief.org/analysis-how-carbon-cycle-feedbacks-could-make-global-warming-worse/
