Relaxing the well-mixed greenhouse gas approximation in climate simulations: Consequences for stratospheric climate

[1] The climatic consequences of relaxing the uniform greenhouse gas (GHG) assumption in the Canadian Centre for Climate Modelling and Analysis atmospheric general circulation model are examined. A simple chemical loss parameterization for nitrous oxide, methane, CFC-11, and CFC-12 is employed that includes stratospheric water vapor production from methane oxidation. Multidecadal mean distributions of these species are obtained that compare reasonably well with UARS satellite observations of the stratosphere. The radiative impact of these changes is a widespread cooling of the stratosphere (with a spatially averaged, annual mean value of 0.6 K), compared to the model with specified uniform GHG distributions. This cooling results from an approximate doubling of the amount of middle to upper stratospheric moisture (as a result of methane oxidation) and exceeds the radiatively induced warming due to decreases in the other GHGs. Annual mean temperature changes of up to +8 K in the upper winter polar stratosphere, by contrast, are dynamically induced because of increases in the residual mean circulation and associated heating.