Left panel: [O] trend (black) and related models obtained by applying the second-degree polynomial fit with (blue) and without (green) considering [CO₂] trend. Middle panel: Scatter plot of [O] trend and related models obtained by applying the second-degree polynomial fit with (blue) and without (green) considering [CO₂] trend. Right panel: Time profile of the ratio between [O] trend and the regressed models, according to the same colour code of the previous panel. The related dashed lines indicate the linear fit evaluated for the two curves.