Abstract
Abstract. Stratospheric ozone recovery is expected to figure prominently in twenty-first century climate change. In a recent paper, Hu et al. (2011) argue that one impact of ozone recovery will be to enhance the warming of the surface-troposphere system produced by increases in well-mixed greenhouse gases. Furthermore, this enhanced warming would be strongest in the Northern Hemisphere, which is surprising since previous studies have consistently shown the effects of stratospheric ozone changes to be most pronounced in the Southern Hemisphere. Hu et al. (2011) base their claims largely on differences in the simulated temperature change between two groups of CMIP3 (Coupled Model Intercomparison Project 3) climate models, one group which included stratospheric ozone recovery in its twenty-first century simulations and a second group which did not. Both groups of models were forced with the same increases in well-mixed greenhouse gases according to the A1B emissions scenario. In the current work, we compare the surface temperature responses of the same two groups of models in a different experiment in which atmospheric CO2 was increased by 1% per year until doubling. We find remarkably similar differences in the simulated surface temperature change between the two sets of models as Hu et al. (2011) found for the A1B experiment, suggesting that the enhanced warming which they attribute to stratospheric ozone recovery is actually a reflection of different responses of the two model groups to greenhouse gas forcing.
Highlights
It is well established that stratospheric ozone depletion has played a dominant role in driving Southern Hemisphere (SH) climate change during the second half of the twentieth century
We evaluate simulated changes in monthly surface air temperature (SAT) from both groups of models, for two different experiments: (1) the A1B experiment considered by H11, and (2) an experiment in which atmospheric CO2 is increased by 1 % per year until it doubles after ∼70 yr
Phys., 12, 4893–4896, 2012 www.atmos-chem-phys.net/12/4893/2012/. In both experiments occurring over the Arctic Ocean in DJF (Fig. 1c and d). We find these trend differences to be associated with greater Arctic sea ice loss in the GROUP1 models relative to the GROUP2 models
Summary
It is well established that stratospheric ozone depletion has played a dominant role in driving Southern Hemisphere (SH) climate change during the second half of the twentieth century (e.g., see Polvani et al, 2011b and references therein). Stratospheric ozone changes significantly alter the radiative heating in the polar lower stratosphere with resulting impacts on stratospheric temperatures. Ozone recovery has the opposite effect on the tropospheric circulation, favoring an equatorward shift of the jet and Hadley cell, and a negative SAM trend. This effect of ozone recovery is expected to largely cancel the effect of increasing greenhouse gases (GHGs) during the 50 yr, resulting in minimal forced circulation changes in the SH during DJF (Shindell and Schmidt, 2004; Son et al, 2010; Polvani et al, 2011a; McLandress et al, 2011)
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