Modelling studies for the SPARC Temperature

Trends Sub-Group

Keith Shine

October 2005

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

Issues

• Coupled versus imposed (ozone) trends?

• ensembles?

• do we still need intercomparisons!?

• do we only use GCMs? (Parameter space, radiation schemes etc)

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!

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

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)

Hundreds of other diagnostic sub-projects including….

trends or evaluation?

“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

Recommendation

• we explore use of 20C3M and CCMVal runs

• otherwise we use “literature review” of available simulations