Quantifying the feedback between ocean heating and CO 2 solubility as an equivalent carbon emission

There are inherent difficulties in quantifying carbon cycle‐climate feedbacks over the 21st century because the system is in a transient state. The conventional approach of deriving gain factors only strictly applies at equilibrium, and they differ with scenario and with respect to different climate variables (e.g., CO 2 , radiative forcing, and temperature) which have different time lags. Here we show that the positive feedback whereby ocean heating reduces the solubility of CO 2 can be quantified in a scenario‐independent way, directly from ocean heat content changes, by expressing it as an ‘equivalent carbon emission’. On annual to centennial timescales, the feedback has the same impact on atmospheric CO 2 as an equivalent emission flux of fossil fuel carbon. From ocean heat‐content data we quantify the ocean heating‐CO 2 solubility positive feedback, which increased in average strength from an equivalent emission of ∼0.08 PgC yr −1 over 1961‐2003 to ∼0.19 PgC yr −1 during 1993‐2003.