Abstract
Abstract. Three recently-completed sets of simulations of multiple chemistry-climate models with greenhouse gases only, with all anthropogenic forcings, and with anthropogenic and natural forcings, allow the causes of observed stratospheric changes to be quantitatively assessed using detection and attribution techniques. The total column ozone response to halogenated ozone depleting substances and to natural forcings is detectable in observations, but the total column ozone response to greenhouse gas changes is not separately detectable. In the middle and upper stratosphere, simulated and observed SBUV/SAGE ozone changes are broadly consistent, and separate anthropogenic and natural responses are detectable in observations. The influence of ozone depleting substances and natural forcings can also be detected separately in observed lower stratospheric temperature, and the magnitudes of the simulated and observed responses to these forcings and to greenhouse gas changes are found to be consistent. In the mid and upper stratosphere the simulated natural and combined anthropogenic responses are detectable and consistent with observations, but the influences of greenhouse gases and ozone-depleting substances could not be separately detected in our analysis.
Highlights
As concentrations of anthropogenic halogenated Ozone Depleting Substances (ODSs) peak in the stratosphere and begin to fall, greenhouse gas (GHG) increases are expected to become an increasingly important driver of future stratospheric ozone trends (e.g. WMO, 2007), the evolution of ozone as ODSs decrease is not expected to be a simple reversal of historical trends (e.g. Jonsson et al, 2009; Waugh et al, 2009)
Overall the agreement appears good between the observations and the total ozone anomalies simulated in response to combined anthropogenic and natural forcings (ALL, corresponding to the REF-B1 simulations) (Chapter 3 of SPARC Chemistry-Climate Model Validation (CCMVal), 2010)
Total column ozone changes simulated in response to combined anthropogenic and natural forcings are broadly consistent with observations, but while the ODS and natural responses are detectable in the observations, the GHG response is not detectable
Summary
As concentrations of anthropogenic halogenated Ozone Depleting Substances (ODSs) peak in the stratosphere and begin to fall, greenhouse gas (GHG) increases are expected to become an increasingly important driver of future stratospheric ozone trends (e.g. WMO, 2007), the evolution of ozone as ODSs decrease is not expected to be a simple reversal of historical trends (e.g. Jonsson et al, 2009; Waugh et al, 2009). Several studies have examined the causes of stratospheric temperature change in chemistry-climate models (Jonsson et al, 2009; Plummer et al, 2010; Stolarski et al, 2010), and others have compared trends in GCMs with limited stratospheric resolution and prescribed ozone changes with observations (Santer et al, 2003; Cordero and Forster, 2006; Ramaswamy et al, 2006). These studies have generally concluded that ozone or ODSs have been the dominant driver of observed lower stratospheric cooling. We make use of newly-completed Chemistry-Climate Model Validation (CCMVal) activity simulations with greenhouse gas changes only (Eyring et al, 2010), as well as earlier sets of simulations with anthropogenic and combined anthropogenic and natural forcings (Chapter 2 of SPARC CCMVal, 2010), to examine the causes of observed changes in stratospheric ozone and temperature, and to test for consistency between models and observations
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