date: Tue, 13 Apr 1999 09:01:48 +0100 from: "Andrew White" subject: Re: HadCM3 CO2 concentrations to: mgrc@ite.ac.uk, "N.W.Arnell" , Andrew White , Matt Livermore , Mike Hulme , Sari Kovats , gjjenkins@meto.gov.uk, jfbmitchell@meto.gov.uk, parryml@aol.com, r.nicholls@mdx.ac.uk Dear Fast-trackers I do not think the key findings from the ecosystem group will be effected by these inconsistencies. Much of the vegetation change and dieback is triggered by climatic change. The CO2 concetration may effects the magnitude of this change but not as significantly as the variation in climatic terms. I am confident that our key results would still hold under the different CO2 concentration scenarios. Yours Andy White Mike hulme wrote>>>>>>>>>>>>>>>>>>>>>>>> Dear Fast-trackers, In putting the scenario paper together for the GEC issue, John Mitchell and I have come up with slightly different CO2 concentrations for HadCM2 and HadCM3 to what we had earlier assumed. These CO2 concentrations will really have to appear in the scenario paper to be consistent with the GCM experiments. Given the differences from the values (I think) you have all used in the impacts work, what significance does this have for your work? HadCM2 HadCM3 assumed 'correct' assumed 'correct' 2020s 441 470 457 434 2050s 565 590 574 528 2080s 731 770 712 638 The difference is that the assumed HadCM2 concentrations are 20-30ppmv too low while the assumed HadCM3 concentrations are 20-70ppmv too high. The assumed HadCM2 concentrations came from Cox and Friend (they had already run Hybrid with these concentrations before the FT work got under way, so we adopted their values). I cannot yet trace where the assumed HadCM3 concentrations came from, but the 'correct' values are what both John Mitchell and the IPCC (1996 report) have calculated for the IS92a scenario. Your suggestions on how best to handle this inconsistency would be appreciated. How big a difference do these differences make to your impacts?