Atmospheric ozone as a climate gas

Observations during the past few decades indicate that the distribution of atmospheric ozone has been changing, notably decreases in the lower stratosphere around the globe and increases in the upper troposphere in the mid-to-high latitudes of the Northern Hemisphere. These changes can perturb the radiative forcing of the Earth-atmosphere climate system and thus raise the issue of atmospheric ozone as a climate gas. Here, we demonstrate the importance of ozone to climate by comparing general circulation model (GCM) simulated present climates between two atmospheric ozone climatologies: a version currently used in the NCAR GCM's (CCM1 and GENESIS) and an updated version. The new ozone climatology includes two improvements: the use of recent years' measurements from satellite (TOMS and SAGE) and ground-based ozonesondes and the consideration of longitudinal variations. Although the effect on the simulated global, annual mean surface air temperature is calculated to be small, the regional influences are quite substantial, especially at the middle and high latitudes of the Northern Hemisphere during winter. This suggests that atmospheric ozone is important in simulating the regional climate and observed ozone changes in the last few decades may have played an important role in affecting the climate. Note that to assess the climatic effect of ozone changes requires the GCM's to include interactive radiation-chemistry-dynamics interaction so that the ozone distribution can be consistently calculated.