The oceanic response to carbon emissions over the next century: investigation using three ocean carbon cycle models

A recent study of coupled atmospheric carbon dioxide and the biosphere (Cox et al., 2000, Nature,408, 184–187) found alarming sensitivity of next-century atmospheric pCO₂ (and hence planetary temperature) to uncertainties in terrestrial processes. Here we investigate whether there is similar sensitivity associated with uncertainties in the behaviour of the ocean carbon cycle. We investigate this important question using three models of the ocean carbon cycle of varying complexity: (1) a new three-box oceanic carbon cycle model; (2) the HILDA multibox model with high vertical resolution at low latitudes; (3) the Hadley Centre ocean general circulation model (HadOCC). These models were used in combination to assess the quantitative significance (to year 2100 pCO₂) of potential changes to the ocean stimulated by global warming and other anthropogenic activities over the period 2000–2100. It was found that an increase in sea surface temperature and a decrease in the mixing rate due to stratification give rise to the greatest relative changes in pCO₂, both being positive feedbacks. We failed to find any comparable large sensitivity due to the ocean.