Overall, there is medium confidence on three outcomes in the ocean from projected CO 2 uptake under medium to high CO 2 concentration scenarios: (i) a weakening of the buffering capacity, which impacts the airborne fraction via the reduction of the ocean CO 2 buffering capacity due to cumulative ocean CO 2 uptake, which reduces the net ocean CO 2 uptake ratio to anthropogenic CO 2 emissions (Katavouta et al., 2018; Arora et al., 2020; Rodgers et al., 2020); (ii) an amplification of the seasonal cycle of CO 2 variables, which impacts both the ocean sink and ocean acidification (Hauck et al., 2015); (iii) a decrease in the aragonite and calcite saturation levels in the ocean, which negatively impacts the calcification rates of marine organisms