From	David Viner - Climate Impacts LINK Project	Date	Tue, 18 May 1999 11:48:40 +0100
To	Mike Hulme, Sarah Raper
Subject	Fwd: Re: Climate Sensitivity
Mike The climate sensitivity of HadCM2.....pick a value between 2.5 and 4.1K D >Envelope-to: f046@cpca11.uea.ac.uk >Date: Tue, 18 May 1999 11:27:48 +0100 (BST) >From: T Johns >Subject: Re: Climate Sensitivity >To: d.viner@uea.ac.uk >Cc: tcjohns@meto.gov.uk >Status: > >Hi David, > >I have just got back from leave today - sorry for the lack of response >to your emails. > >On climate sensitivity, the equilibrium sensitivity in HadCM2 was difficult >to get a definitive answer for initially as the conventional slab experiment >was unstable, so we estimated it from part of a transient coupled run >instead. We quoted 2.5 K in the original Nature paper. Recently we >have done a HadAM2 slab experiment (modified sea ice and slab ocean physics) >which indicated 4.1 K rather than 2.5 as an equilibrium value. This is >quoted in a paper submitted as a CMIP study. The HadAM3 conventional >slab experiment gave the 3.3 K figure I think. The HadCM2 discrepancy >indicates the perils of this yardstick; other research here suggests that >the effective climate sensitivity does respond to climate change feedbacks >in transient experiments (with HadCM2 particularly). The early 2.5 K >estimate has been revised upwards based on a long coupled run of HadCM2 to >be closer to the 3.3 K we got from HadCM3 equilibrium slab experiments. > >Comparing transient temperature responses to similar time-varying forcing >may be a better indication of real sensitivity, but so long as we quote >single climate sensitivity numbers I fear that there is scope for confusion. > >Tim. > >PS: I will try to get an update on the HadCM3 references sorted out for you. > >> Tim >> >> I'm a bit confused as now I have seen a numeber of different values, in >> HCTN2 you mention that HadAM3 has a climate sensitivity of 3.3 degrees K >> and that this is similar to HadCM2. Is this the case and is such a value >> available from a comparable HadAM2 experiment. >> >> Many regards >> >> David >> >> PS Did you get my message about references? > #-------------------------------------------- # Dr. David Viner # Climate Impacts LINK Project # Climatic Research Unit # University of East Anglia # Norwich NR4 7TJ # UK # mailto://d.viner@uea.ac.uk # WWW: http://www.cru.uea.ac.uk/link # WWW: http://ipcc-ddc.cru.uea.ac.uk # Tel: +44 (0)1603 592089 # Fax: +44 (0)1603 507784 #---------------------------------------------