Marine ecosystem is influenced by multiple factors under the global warming. Increasing temperature raises the matabolic demand for oxygen, however, its supply declines as the concentration of dissolved oxygen decreases. Metabolic index is defined as the oxygen supply to demand ratio for a marine organism, quantitatively combining the effects of ocean warming and deoxygenation. A subset of the earth system models participating in the Coupled Model Intercomparison Project phase 6 (CMIP6) are used to calculate the century-scale changes in the metabolic index under three different scenarios. Under the most aggressive warming scenario, metabolic index can decline over 50\% at northern extratropics including the US west coast. Overall magnitude of the change is dependent on the emission scenarios, whereas spatial patterns are model-dependent, in particular at low latitudes due to the large uncertainty in projected oxygen changes.