The potential impact on atmospheric ozone and temperature of increasing trace gas concentrations

Abstract

The response of the atmosphere to emissions of chlorofluorocarbons (CFCs) and other chlorocarbons and to increasing concentrations of other radiatively active trace gases such as CO2, CH4, and N2O is calculated by means of a coupled chemical‐radiative‐transport one‐dimensional model. It is shown that significant reductions in the ozone concentration and in the temperature should be expected in the upper stratosphere as a result essentially of increasing concentrations of active chlorine produced by photo decomposition of the CFCs. For a constant emission of chlorofluorocarbons‐11 and ‐12 at approximately the 1980 level (309 kT/yr for F‐11 and 433 kT/yr for F‐12) the calculated decrease (assuming no other changes) in the ozone concentration relative to the preindustrial atmosphere is approximately 60–70% at 40 km, and the reduction in the ozone column is 8.7% when temperature feedback is included in the model and 5.5% when it is omitted. The model also shows that a doubling of CO2 leads to a 1.8% increase in the ozone column abundance and a 2 K increase in the surface temperature. At 40 km the ozone density is enhanced by 15% and the temperature reduced by 8 K. A doubling of methane produces a 2.4% increase in the ozone column. A 20% enhancement in the nitrous oxide content leads to an ozone depletion of 1.4%. Time‐dependent calculations of ozone and temperature show that if the production of F‐11 and F‐12 increases by 3%/yr until it reaches a capacity cap equal to 1.5 times the 1985 world production level, the maximum ozone depletion should be of the order of 4–5%, assuming a growth in the concentration of CO2, CH4, and N2O of about 0.5, 1.0, and 0.25%/yr, respectively. For this scenario the maximum ozone depletion is found to occur in year 2070. The slight increase appearing after 2070 is directly dependent on the future growth in the methane concentration. If the production of F–11 and F–12 increases continuously by 3%/yr, without capacity cap, and if the changes in the concentration of other trace gases are ignored, the ozone column abundance is predicted to be reduced by more than 10% after year 2050. The model shows an almost linear relation between the ozone depletion and the chlorine content as long as the mixing ratio of active chlorine remains smaller than that of active nitrogen. The O3/Clx sensitivity, however, is a strong function of NOy content. For amounts of chlorine comparable or larger than those of active nitrogen the ozone depletion increases rapidly with the amount of chlorine present in the atmosphere.

Long-term trends in the ionospheric F2 region with different solar activity indices

“…Therefore, we have to extrapolate our trend values to an interval corresponding to such a doubling of the greenhouse gases. According to Houghton et al (2001) and Brasseur and de Rudder (1987), the content of the atmospheric greenhouse gases increased about 20 % during 40 years. Assuming a linear relationship between the amount of the greenhouse gases and the ionospheric effect, then for the doubling of the greenhouse gases the experimental trends have to be multiplied by 200 to get the ionospheric effect which can be compared with the model values.…”

Trends in the ionospheric E and F regions over Europe

“…To compare these theoretical results with our experimental trend data it is necessary to take into account the real changes of these gases during the last 40 y, corresponding to the main interval of ionosonde observations which has been analysed here. After the recent IPCC report (Houghton et al, 1996) and Brasseur and de Rudder (1987) the atmospheric content of these gases has increased during the last 40 y for CO 2 by about 15%, CH 4 by about 44%, N 2 O by about 7% and for the CFCs and HCFCs partly by essentially higher rates (yearly increases between 0.5%). Taking into account the dierent amounts of these greenhouse gases, for the total direct radiative forcing, after Houghton et al (1996) an eective increase of the greenhouse gases of about 20% can be assumed for the last 40 y.…”

Investigations of long-term trends in the ionosphere with world-wide ionosonde observations*

“…Their theoretical results have been derived for a doubling of the atmospheric greenhouse gases CO 2 and CH 4 . The effective change of the greenhouse gases during the last 40 years where trends of the ionosonde data have been investigated is about 20% (Brasseur and de Rudder, 1987;Houghton et al, 2001). Assuming a linear dependence between the content of the atmospheric greenhouse gases and the ionospheric effect, the experimental trends can be extrapolated to a level of doubled greenhouse gases.…”