date: Sat Feb 2 19:09:40 2002 from: Mike Hulme subject: Fwd: RE: UKCIP confidences to: j.turnpenny@uea.ac.uk Date: Tue, 29 Jan 2002 13:54:02 +0000 From: "Mitchell, John FB" Subject: RE: UKCIP confidences To: 'Mike Hulme' Cc: "Senior, Cath" , "Wood, Richard" X-Mailer: Internet Mail Service (5.5.2653.19) Hi Mike I've put some comments in the text. Having said repeatably for good reason that regional climate change is very uncertain, I think we have to be very careful not to get carried away in UKCIP. With best wishes John John F B Mitchell, Head of Modelling Climate Change Met.Office, Hadley Centre for Climate Prediction and Research London Road, Bracknell, RG12 2SY UK Tel +44 (0)1344 856613/6656 Fax+44 (0)1344 856912 E-mail john.f.mitchell@metoffice.com [1]http://www.metoffice.com/research/hadleycentre > -----Original Message----- > From: Mike Hulme [SMTP:m.hulme@uea.ac.uk] > Sent: Monday, January 28, 2002 9:32 AM > To: Mitchell, John FB > Cc: Senior, Cath; Jenkins, Geoff; Jones, Richard; j.turnpenny@uea.ac.uk > Subject: Re: UKCIP confidences > > John (and others), > > Thanks for the comments on the confidence levels for the UKCIP02 report. > I have been through these and am happy to go with most of your suggested > changes. But I have the following five statements where I would propose a > slightly different resolution, plus one additional one re. THC. > > > Temperature > 1. "SE>NW gradient": could we retain the 'H' confidence if we restricted > this just to summer? There is certainly better model agreement for this > gradient in summer, and the physical basis should be better > continentality, the winter role of the ice-albedo f/b at higher latitudes > counter-acting this gradient is absent, the weakening of the THC leads to > reduced NW warming > [Mitchell, John FB] My reason for suggesting medium was that ist does > depend to a large extent on the land surface and cloud parameterizations- > both of which we have limited physical understanding. having said that, > summer drying in the southern half of Europe is I think a featrure of most > , if not all recent models, and the continentality and THC/deep mixing in > the ocean do provide some physical explanantion. > 2. "Night>day in winter, Day>night in summer": I had 'M' and you suggest > 'L'. I would have thought the physical basis for this is reasonable > greater cloud in winter but higher humidity, and less cloud in summer > allowing greater insolation. Not sure about other models, but I would > have thought 'M' is reasonable. [Mitchell, John FB] Humidity changes > alone I suspect are not enought to explain this, and I don not think that > one can put anything more than L on something that depends on cloud- why > dose the cloud increase? Again why odes summer cloud decrease- becasue > the surface dries- but the surface dries because of reductions in cloud > cover. Cloud cover: > 3. "Reduction in summer cloud, esp. in south": you had only 'L', I had > 'M'. I would have thought a consistent picture is being told here > reduced cloud, reduced precip. (which we give 'M' for), reduced soil > moisture (which we give 'M' for), and increased in summer DTR (see above). > Hard to argue that with these other changes we would actually get > increased summer cloud. > [Mitchell, John FB] See comments above about cloud generally- > precipitation is faily consistent across models , but has anyone looked at > cloud- also it is possible have precip decrease but more boundary layer > stratus because of a more statically stable atnosphere- think of SE > England with easterlies. > > Wind > 4. "Average windspeeds increase more over south than north" I had 'L', > but you would rather omit. If we exclude this one then we will have no > headline statements about wind. I agree that model consistency will be > low, but the physical reasoning I would have thought is due to the > circulation changes and storm tracks pushing further south if Had3AMH > model is worth anything then isn't it giving us greater confidence about > storm tracks. I would prefer to retain an 'L' here. > [Mitchell, John FB] Have you looked at the winds over land? They are > awful. I have no physical explanantion for th changes, I doubt if ti is > statistically significant, and HadCM2 had different changes. I appreciate > we have no headline statements about wind- but I don't think we should be > putting something as flaky as this in a headline statement. Soil moisture: > 5. "Decreases in summer, esp. in SE": you had 'M' and I had 'H'. This is > part of the story above, reduced cloud, reduced precip, increased DTR, and > therefore reduced soil moisture. Even though precip. change in summer may > only be 'M', surely there is greater physical basis to think that soil > moisture levels will decrease with large summer warming? I would prefer > to retain 'H'. > [Mitchell, John FB] As I noted above, we are not sure what triggers the > drying. I suspect it is mainly a combination of reduced precipitation and > increased evaporation. The reduced preciptitation does seem to be a large > scale response in the SRES runs ( ie not merely a local feedback with the > land surface) but I would still feel slightly uncomfortable with H. M or > H, I would definitely confine the bullet to the SE > One statement that seemed to get lost was this one. It should be accorded > a 'H' status. > > 6. "Although the strength of the Gulf Stream may weaken in future, it is > very unlikely that this would lead to a cooling of UK climate over the > next century". > [Mitchell, John FB] I agree > Or if you don't like this one, some other equivalent that makes some > clear statement about THC and that we are not going to 'freeze' in the > foreseeable future!! > > > Thanks I'd be interested in your views. Would be happy to discuss these > on the phone sometime if you think we need to. > [Mitchell, John FB] I am around most of this week- Linda (01344 856656) > usually can find me if I am wandering round the building,- next week I am > running a mmeting Mon- Thurs AM > John > > > > At 16:47 23/01/02 +0000, Mitchell, John FB wrote: > > > Dear Mike > > Sorry about the incomplete email - finger trouble. It stopped at a > particularly inappropriate point! I also discovered I had mssed some > of the > Table I assume the Table is a high level summary and hence should > contain > that which is useful and in which we have reasonable confidence > > I attach comments on the revised table of confidence levels- I have > tried to > assess the levels using the three criteria- physical understanding, > consistency amongst models and statistical significance ( in the > Hadx3 > models). In many cases this information is not available, so I have > had to > guess. Richard agrees there is no time to carry out statistical > tests on all > the variables mentioned (ideally what we should have done), and in > most > cases, we do not have information from other models.I talked with > Richard > and Cath about the confidence levels. Richard, I understand, will > see you > tomorrow (Thurs) . > > I have denoted by a **** where we disagree with the draft > assessment, (in > one case, I think the table is wrong- temp seasonality increases- > this > should have at most the same confidence that summer/autumn warm more > than > winter/spring (in my view low)) and we have no confidence in the low > level > winds, especially over land. Some of the quantities didn't seem to > useful to > me, and could be left out (especially if they are low confidence) We > would > leave lightning and fog out as they are based on empirical indices > which are > not well validated.I n general we are not sure how useful statements > on > seasonality are, and the seasonal variation in the UK is not > currently well > defned in many regions anyway. I don't think we have any confidence > in > winter temperatures being more variable ( in most regions in most > models the > opposite is true as albedo feedback reduces temperature gradients) . > > I don't think we should put the reasons for the assessment in the > report, > but we should keep a record of how we have assigned the confidences > in the > final verison of the report > > WIth best wishes > John > > > > > > John F B Mitchell, Head of Modelling Climate Change > Met.Office, Hadley Centre for Climate Prediction and Research > London Road, Bracknell, RG12 2SY UK > Tel +44 (0)1344 856613/6656 Fax+44 (0)1344 856912 > E-mail john.f.mitchell@metoffice.com > <[2]http://www.metoffice.com/research/hadleycentre> > > >