Atmospheric trace gases and global climate: a seasonal model study

Observations have shown that concentrations of atmospheric trace gases CO₂, CFCs, CH₄ and N₂O have been increasing and the trend of increases will most likely continue. Increases of these radiatively and chemically important trace gases may have implications for global climate both directly by modifying the earth’s radiation budget and indirectly by changing atmospheric O₃ distribution. Here, we use atmospheric models with seasonal cycles to study the changes in latitudinal and vertical distributions of atmospheric O₃ and temperature caused by increases of trace gases in the next few decades. It is found that increases of CFCs, CH₄, and N₂O may augment the surface warming expected from CO₂ increases. Using projected trends of CO₂, N₂O, CH₄ and CFCs, our calculations showed that the annual mean and global mean surface temperature could warm by as much as 2.5 °C with larger warming at high latitudes by the middle of the next century. The calculations also suggest that the warming in the lower stratosphere and upper troposphere is much larger than that at the surface, especially during the summertime. Large stratosphere cooling is calculated with maximum cooling of ~ 12 °C around 45 km, where O₃ depletion caused by increases of trace gases contributes substantially to the total cooling. However, the effects of O₃ changes on the temperatures below 40 km appear to be small because of the small changes calculated in the O₃ distribution.