Modelling studies for the SPARC Temperature Trends Sub-Group Keith Shine October 2005.
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Transcript of Modelling studies for the SPARC Temperature Trends Sub-Group Keith Shine October 2005.
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Modelling studies for the SPARC Temperature
Trends Sub-Group
Keith Shine
October 2005
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What do we want?
• To develop a consensus understanding of the drivers of temperature trends
• Particular attention needs to be given to the time evolution of those trends
• Previous studies have been dominated by comparing linear trends and comparing annual-mean trends
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Issues
• Coupled versus imposed (ozone) trends?
• ensembles?
• do we still need intercomparisons!?
• do we only use GCMs? (Parameter space, radiation schemes etc)
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How? – various possibilities
• Relying on a small sample of models running fully resolved stratospheres
• “aftercomparisons” (e.g. Shine et al.)
• “Intercomparisons of opportunity” (CCMval – see Ulrike’s talk, IPCC)
• Launching our own tight intercomparison exercise – no!
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http://www-pcmdi.llnl.gov/ipcc/about_ipcc.php
17-ish modelling groups doing “climate of 20th century” (20C3M) runs with varying numbers doing other scenarios.
Standard output for the 20C3M runs goes “only” to 10 hPa
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Not all models include all forcings – I doubt whether any include imposed stratospheric water vapor, or solar driven ozone changes
(Table from Santer et al. 2005, Science, Supp Material)
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Hundreds of other diagnostic sub-projects including….
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trends or evaluation?
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“aftercomparisons”• Take available calculations by various
groups with stratospheric resolution
• Advantage – little overhead on participating groups – they supply results from the calculations they have performed; fewer constraints means wider parameter space!
• Disadvantage – apples versus oranges
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Recommendation
• we explore use of 20C3M and CCMVal runs
• otherwise we use “literature review” of available simulations