These data were collected at Shannon Point Marine Center in Washington, U.S.A. in March, 2021. Embryos were reared at either 10C (ambient), 12C, 14C, or 16C  and at either ~500 pCO2 uatm (ambient) or ~2000 pCO2 uatm (heightened). These data measure the oxygen consumption rates (MO2)  response of winter-spawned Pacific herring embryos to variations in rearing temperature and pCO2 levels. The results evaluate if rearing conditions affect survival during a marine heatwave and the CTmax temperature and duration at which survival diminishes.