Tuesday, November 29, 2011


date: Sat Feb 2 19:09:40 2002
from: Mike Hulme <m.hulmeatXYZxyz.ac.uk>
subject: Fwd: RE: UKCIP confidences
to: j.turnpennyatXYZxyz.ac.uk

Date: Tue, 29 Jan 2002 13:54:02 +0000
From: "Mitchell, John FB" <john.f.mitchellatXYZxyzoffice.com>
Subject: RE: UKCIP confidences
To: 'Mike Hulme' <m.hulmeatXYZxyz.ac.uk>
Cc: "Senior, Cath" <casenioratXYZxyzoffice.com>,
"Wood, Richard" <rwoodatXYZxyzoffice.com>
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 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.mitchellatXYZxyzoffice.com
> -----Original Message-----
> From: Mike Hulme [SMTP:m.hulmeatXYZxyz.ac.uk]
> Sent: Monday, January 28, 2002 9:32 AM
> To: Mitchell, John FB
> Cc: Senior, Cath; Jenkins, Geoff; Jones, Richard; j.turnpennyatXYZxyz.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
> 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.mitchellatXYZxyzoffice.com
> <[2]http://www.metoffice.com/research/hadleycentre>

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