Increasing CO2 coupled with other anthropogenic perturbations: Effects on ozone and other trace gases

The GSFC 2D interactive chemistry-radiation-dynamics model has been used to study the effects on stratospheric trace gases of past and future CO2 increases coupled with changes in CFC's, methane, and nitrous oxide. Previous simulations with the GSFC model showed that the stratospheric cooling calculated to result from doubling atmospheric CO2 would lead, in the absence of a growth of other anthropogenic gases, to a decrease in upper stratospheric NOy of roughly 15%. This work has been extended to examine the chemical and dynamical impact of increases in anthropogenic gases during the time period 1960 to 2050. The simulations have been carried out with and without changes in CO2. In the low latitude upper stratosphere ozone is predicted to be 12% greater in 2050 than in 1990 when increasing CO2 is included, compared with an increase of only 2% when CO2 is fixed at 1990 values. The recovery of globally averaged column ozone to 1970 values is predicted to occur 15 years earlier with increasing CO2 than without. These differences can be understood by examining the effects of the CO2 increases on the ozone loss rates due to the various catalytic destruction cycles.

Another example of the coupled responses is shown in the simulated behavior of water vapor. Between 1990 and 2050 low latitude water vapor is predicted to increase by 8% in the lower stratosphere without increasing CO2, due mainly to the increasing methane concentrations. When CO2 is allowed to change, this water vapor increase rises to 16% as a result of the warming of the tropical tropopause.