RESPONSE OF A COUPLED OCEAN-ATMOSPHERE MODEL TO INCREASING ATMOSPHERIC CARBON-DIOXIDE

This study investigates the response of a climate model to a 1% per ye ar increase of atmospheric carbon dioxide. The model is a general circ ulation model of the coupled ocean-atmosphere-land surface system, wit h a global computational domain, smoothed geography, and seasonal vari ation of insolation. The simulated increase of sea-surface temperature is very slow in the northern North Atlantic and the Circumpolar Ocean of the Southern Hemisphere where the vertical mixing of water penetra tes very deeply and the rate of deep water formation is relatively fas t. Extending this work, we investigated the transient responses of the coupled model to the doubling and quadrupling of atmospheric CO2, ove r the period of several centuries. During the entire 500-yr period of the experiment, the global mean surface air temperature increases almo st 3.5-degrees-C when CO2 is doubled, and 7-degrees-C when it is quadr upled. In the latter experiment, the thermal structure and dynamics of the model oceans undergo drastic changes, such as cessation of the th ermohaline circulation in most of the model oceans, and substantial de epening of thethermocline, especially in the North Atlantic. These cha nges prevent the ventilation of the deeper layer of the oceans and, if they occurred in reality, could have a profound impact on the carbon cycle and biogeochemistry of the coupled ocean-atmosphere system.