A 2-DIMENSIONAL MODEL WITH COUPLED DYNAMICS, RADIATIVE-TRANSFER, AND PHOTOCHEMISTRY .2. ASSESSMENT OF THE RESPONSE OF STRATOSPHERIC OZONE TO INCREASED LEVELS OF CO2, N2O, CH4, AND CFC

The impact of increased levels of carbon dioxide (CO2), chlorofluoroca rbons (CFCs), and other trace gases on stratospheric ozone is investig ated with an interactive, two-dimensional model of gas phase chemistry , dynamics, and radiation. The scenarios considered are (1) a doubling of the CO2 concentration, (2) increases of CFCs, (3) CFC increases co mbined with increases of nitrous oxide (N2O) and methane CH4, and (4) the simultaneous increase Of CO2, CFCs, N2O, and CH4. The radiative fe edback and the effect of temperature and circulation changes are studi ed for each scenario. For the double CO2 calculations the tropospheric warming was specified. The CO2 doubling leads to a 3.1% increase in t he global ozone content. Doubling of the CO2 concentrations would lead to a maximum cooling of about 12-degrees-C at 45 km if the ozone conc entration were held fixed. The cooling of the stratosphere leads to an ozone increase with an associated increase in solar heating, reducing the maximum temperature drop by about 3-degrees-C. The CFC increase f rom continuous emissions at 1985 rate causes a 4.5% loss of ozone. For the combined perturbation a net loss of 1.3% is calculated. The struc ture of the perturbations shows a north-south asymmetry. Ozone losses (when expressed in terms of percent changes) are generally larger in t he high latitudes of the southern hemisphere as a result of the eddy m ixing being smaller than in the northern hemisphere. Increase of chlor ine leads to ozone losses above 30 km altitude where the radiative fee dback results in a cooler temperature and an ozone recovery of about o ne quarter of the losses predicted with a noninteractive model. In all the cases, changes in circulation are small. In the chlorine case, ci rculation changes reduce the calculated column depletion by about one tenth compared to offline calculations.