Modeled impacts of stratospheric ozone and water vapor perturbations with implications for high‐speed civil transport aircraft

Ozone and water vapor perturbations are explored in a series of experiments with the Goddard Institute for Space Studies climate/middle atmosphere model. Large perturbations to stratospheric ozone and water vapor are investigated, with and without allowing sea surface temperatures to change, to illuminate the nature of the dynamic and climatic impact. Then more realistic ozone and water vapor perturbations, similar to those estimated to result from aircraft emissions, are input and the equilibrium response obtained. Removing ozone in the lower stratosphere without allowing sea surface temperatures to change results in in situ cooling of up to 10°C in the tropical lower stratosphere, with radiative warming about half as large in the middle stratosphere. The temperature changes induce increases in tropospheric and lower stratospheric eddy energy and in the lower stratosphere residual circulation of the order of 10%. When sea surface temperatures are allowed to respond to this forcing, the global, annual‐average surface air temperature cools by about 1°C as a result of the decreased ozone greenhouse capacity, reduced tropospheric water vapor, and increased cloud cover. For more realistic ozone changes, as defined in the High‐Speed Research Program/Atmospheric Effects of Stratospheric Aircraft reports, the stratosphere generally cools by a few tenths degrees Celsius. In this case, the surface air temperature change is not significant, due to the conflicting influences of stratospheric ozone reduction and tropospheric ozone increase, although high‐latitude cooling of close to 0.5°C does occur consistently. Doubled stratospheric water vapor cools the middle atmosphere by 2°–3°C and warms the upper troposphere by 0.5°C. Reduced tropospheric‐stratospheric vertical stability leads to tropospheric planetary longwave energy increases of some 15% for the longest waves and stratospheric residual circulation increases of 5%. When sea surface temperatures are allowed to change, the surface air temperature warms by just a few tenths of a degree Celsius; although this change is not significant in terms of the model's natural variability, the experiment is warmer than the control in most years. The response is muted as the high altitude of energy input minimizes surface level feedbacks, and high‐level cloud cover is reduced. With a more realistic increase of stratospheric water vapor of 7%, the middle atmosphere cools by 0.5°C or less, and the surface temperature change is neither significant nor consistent. Overall, the experiments emphasize that stratospheric changes affect tropospheric dynamics in the model, that tropospheric changes can affect stratospheric dynamics, and that tropospheric feedback processes and natural variability are important when assessing the climatic response to aircraft emissions.