07/14/2008
Using Models to Identify the Role of Climate and Atmospheric Composition on Changes in the Lower Stratosphere
Summary
Department of Energy (DOE)-funded scientists have shown that the Community Atmosphere Model Version 3 (CAM3) can reproduce a variety of large-scale changes observed in climate and chemical composition in the stratosphere when forced with the observed sea-surface temperatures and surface concentrations of long-lived trace gases and ozone-depleting substances. They also used the same model to differentiate the role of chemically active composition (ozone, methane, and chlorofluorocarbons) and CO2 observed trends in the stratosphere. The simulations indicate that changes in CO2 do not change the total ozone trend; however, CO2 changes do lead to important differences in ozone in the upper part of the stratosphere. In contrast, changes in surface methane concentration drive changes in the globally averaged total ozone column through changes in tropospheric and stratospheric ozone columns. The model is capable of reproducing trends in the age of tropical air that were found in other studies and suggests that the relation between the upward velocity and mean age of tropical air breaks down in the upper stratosphere, above 20 hPa, in association with isentropic mixing above that level. These simulations suggest that keeping methane and ozone-depleting substances at their 1970 levels would have a significant impact, indicating the potential importance of controlling methane emissions.
References
Lamarque J.-F., D.E. Kinnison, P.G. Hess, and F.M. Vitt. 2008. “Simulated lower stratospheric trends between 1970 and 2005: Identifying the role of climate and composition changes,” J. Geophys. Res. 113 D12301, DOI:10.1029/2007JD009277