Time-Dependent Response of the Climate to Increasing Atmospheric Carbon Dioxide

The thesis describes the development of an intermediate level, primitive equation climate model and the application of the model to the transient CO(,2)-climate problem. The model solves the equations of large scale motion in two atmospheric layers. Longitudinal dependence is expressed as a highly truncated Fourier series. Meridional derivatives are finite differenced with a 3 degree latitude interval. The time step of integration is 2 hours. The surface has stylized geography, and an immobile, isothermal ocean with latitudinally -dependent heat capacity. Radiative processes are highly parameterized in this version of the model. Sensitivity experiments are performed to test the effects of two different assumptions about the amount of ocean that is thermally involved with the atmosphere over the time scale of the atmospheric CO(,2) increase. To simulate the time-dependent nature of the climate response to increasing CO(,2), the model is integrated in time for 100 years. The initial CO(,2) concentration of 300 ppmv is increased with a 2% growth rate in emissions. Doubling (600 ppmv) is reached after 97 years. The rates at which climate variables change during the forcing period are examined, and the values at doubling are compared with the results from an equilibrium doubling experiment with the same model. When the atmospheric CO(,2) concentration is doubled in the model, the globally average surface air temperature increases by 0.8K, with 9K and 5K increases in the Arctic and Antarctic, respectively. Precipitation increases by 8%, with maximum increases near 60 degrees latitude in both hemispheres. The effects of the two different ocean depth distributions are more pronounced in the transient experiments than in the equilibrium experiments. At equatorial latitudes, the equilibrium and transient results at 600 ppmv CO(,2) are very similar. At high latitudes, the transient values have changed less than the equilibrium values. At mid-latitudes in both hemispheres, there are indications that the character, and not just the timing, of the transient response differs from the equilibrium response.