Abstract
Abstract. Future stratospheric ozone concentrations will be determined both by changes in the concentration of ozone depleting substances (ODSs) and by changes in stratospheric and tropospheric climate, including those caused by changes in anthropogenic greenhouse gases (GHGs). Since future economic development pathways and resultant emissions of GHGs are uncertain, anthropogenic climate change could be a significant source of uncertainty for future projections of stratospheric ozone. In this pilot study, using an "ensemble of opportunity" of chemistry-climate model (CCM) simulations, the contribution of scenario uncertainty from different plausible emissions pathways for ODSs and GHGs to future ozone projections is quantified relative to the contribution from model uncertainty and internal variability of the chemistry-climate system. For both the global, annual mean ozone concentration and for ozone in specific geographical regions, differences between CCMs are the dominant source of uncertainty for the first two-thirds of the 21st century, up-to and after the time when ozone concentrations return to 1980 values. In the last third of the 21st century, dependent upon the set of greenhouse gas scenarios used, scenario uncertainty can be the dominant contributor. This result suggests that investment in chemistry-climate modelling is likely to continue to refine projections of stratospheric ozone and estimates of the return of stratospheric ozone concentrations to pre-1980 levels.
Highlights
Over the past four years the chemistry-climate modelling community has made progress in understanding and refining projections of stratospheric ozone over the 21st century
Close to peak ozone calculated by averaging the shi3f0t in the CCSRNIES and WACCM models is shown in the red line
A method introduced and tested for the CMIP3 models has been adapted and developed for models run as part of the Chemistry-Climate Model Validation activity (CCMVal2)
Summary
Over the past four years the chemistry-climate modelling community has made progress in understanding and refining projections of stratospheric ozone over the 21st century. As part of CCMVal, a new analysis of uncertainty in projections of total column ozone over the 21st century and dates of return of total column ozone has been produced (Chapter 9, SPARC CCMVal, 2010) This analysis, has been conducted for reference simulations of CCMs based on a common GHG forcing scenario. In the climate change community, this uncertainty is addressed by producing projections of climate variables using a range of different possible GHG scenarios (Special Report on Emissions Scenarios, Nakicenovic et al (2000)), consistent with economic models of global development. Additional simulations of the CCMs used for the CCMVal intercomparison forced with different GHG scenarios (and in some cases slightly different ODS scenarios) are used to quantify the uncertainty in global and regional stratospheric ozone projections associated with three factors: model uncertainty, scenario uncertainty and internal variability. Identifying regions and time periods where these conditions are found will aid future CCM ensemble design and inform policymakers about the potential to narrow uncertainty in ozone projections
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