Transient Temperature Changes Due to Increasing CO2 Using Simple Models

The effect of the oceanic heat capacity on global temperature response to external forcing is studied by considering a CO2-induced warming. The heat flux into the ocean is calculated using a box-diffusion model, earlier established for simulating the global carbon cycle. The calculated transient warming due to CO2 produced by fossil fuel until 1980 is 0.20 to 0. 26K, or about 50% of the value for radiative equilibrium, corresponding to a delay of 16 to 24 years. Analyses of CO2 in ice cores suggest a lower pre-industrial concentration, e.g. 265 ppm, than previously assumed (c. 290 ppm). The transient temperature increase until 1980 calculated for this case is about twice that for a case which starts from 297 ppm. Comparison with observations since 1880 shows that a long-term warming trend might be due to CO2, but the residual scatter unexplained by CO2 is still large. Finally the different thermal behaviour of oceans and continents is accounted for in a schematic way, considering heat exchange between them. The results indicate stronger temperature variations over the continents than over the sea.