The effect of ocean heat capacity upon global warming due to increasing atmospheric carbon dioxide

Abstract

Time‐dependent global warming due to increasing levels of atmospheric carbon dioxide has been estimated by employing an ocean‐land global climate model. Ocean heat capacity is incorporated by means of a global ocean model having a 70 m deep mixed layer, with heat being transported from the mixed layer to deeper waters by eddy diffusion. The time‐dependent increase in atmospheric CO2, from 1860 to 2025, is taken from carbon‐cycle models. The model results suggest that ocean heat capacity will produce a lag in CO2‐induced global warming of about 2 decades. For example, without inclusion of ocean heat capacity the model predicts that an increase in global surface temperature of 1°C, relative to 1860, will occur by 1988. But when ocean heat capacity is included, the 1°C warming is delayed until 2006–2012, this range of times corresponding to no land‐ocean advective coupling (2006) and complete land‐ocean coupling (2012). By 2025, when the assumed atmospheric CO2 content is twice the 1860 value, the model predicts global warming of 1.5°–1.8°C, in contrast to 3.1°C when ocean heat capacity is neglected.