Wednesday, November 30, 2011

0244.txt

date: Wed Apr 30 09:43:25 2003
from: Mike Hulme <m.hulmeatXYZxyz.ac.uk>
subject: Re: FW: CRU05 current status
to: Tim Mitchell <t.mitchellatXYZxyz.ac.uk>

Depends on status of meeting. If "official" IPCC invite, then DEFRA would (should) agree
to pay your costs. If only an unofficial scoping meeting then perhaps not.
Either way, we can sort something out re. costs if (a) you are invited and (b) you are keen
to go.
Mike
At 15:36 29/04/2003 +0100, you wrote:

Mike,
Phil has been pushing Martin Parry to get me an invite to the IPCC WG1/2
interface meeting on climate change *impact* detection (New York, mid-June).
The other UK invitees are Tim Sparks and Myles Allen.
If I get an official invite, I will need travel funds from some budget or
other. I presume that the co-op budget (50% of my time at present) is the
most likely candidate, but are there sufficient travel funds in there?
Tim
____________________________________
Dr. Tim Mitchell
Tyndall Centre for Climate Change Research
email: t.mitchellatXYZxyz.ac.uk
web: [1]http://www.cru.uea.ac.uk/~timm/
phone: +44 (0)1603 59 3904
fax: +44 (0)1603 59 3901
post: Tyndall, ENV, UEA, Norwich, NR4 7TJ, UK
____________________________________
------ Forwarded Message
From: Phil Jones <p.jonesatXYZxyz.ac.uk>
Date: Tue, 29 Apr 2003 13:57:06 +0100
To: Tim Mitchell <t.mitchellatXYZxyz.ac.uk>
Subject: Re: CRU05 current status
Tim,
You sent me this paper earlier. I said at the time to myself that I
hoped Sarah wasn't
being asked too much about patterns and causes, as she could do with some
education
on some issues. Hopefully your email has helped.
The web site ought to contain a slightly modified version of what
Mike is getting at at the
end of this email. We certainly need this.
I was invited to an IPCC WG1/2 interface meeting on climate change
detection in
New York in the week of June 16. As I'm unable to go I've talked to Kathy
Maskell and to
Martin Parry (the organiser as the initiative comes from WG2) and
suggested they invited
you. If you are able to go then can you represent CRU as well as
Tyndall. I'll forward the
email invitation and I hope they contact you. If you can't make it
suggest Tim Osborn.
The issue of which datasets to use for different applications is an
important aspect to get
across to those going.
Cheers
Phil
At 11:47 28/04/03 +0100, you wrote:
> > When you do a new draft of the paper I would suggest you add in that
> > this data should
> > not be used for climate change detection studies - not this bluntly, but
> > you know what I'm
> > getting at.
>
>Will do.
>
> > Maybe this just needs to go on the web site.
>
>What do you think of the Q and A below? Mike's added his comments at the
>bottom. I'm thinking of adding an edited version of these Q and A to the
>website. I guess that another version could go in the paper.
>
>Tim
>
>------ Forwarded Message
>From: Mike Hulme <m.hulmeatXYZxyz.ac.uk>
>Date: Wed, 09 Apr 2003 14:58:15 +0100
>To: Tim Mitchell <t.mitchellatXYZxyz.ac.uk>
>Subject: Re: CRU interpolated climate
>
>Tim - see my comments at the end .......
>
>
>
>At 16:59 07/04/2003 +0100, you wrote:
> > Sarah,
> >
> > Many questions!
> >
> > I'll answer as best I can, but please do not quote these answers, as I
> ought
> > to collaborate with co-authors before giving any quotable comments.
> >
> >> > I am now thoroughly confused and would be very grateful if you could
> >> > sort me out! I have read your guidelines on the web-site, and need
> >> > help with interpreting the following:
> >> >
> >> > "These choices mean that while this data-set is suitable for using as
> >> > an input to environmental modelling, it is NOT suitable for use in
> >> > detecting climate change. It is NOT a legitimate use of this data-set
> >> > to attempt to prove or disprove the existence of climate change at an
> >> > individual grid-box."
> >> >
> >> > My questions are:
> >> > 1. Is the 1960-2000 climate time series really not to be used at all
> >> > to detect climate change, even over aggregated, regional areas?
> >
> > It depends on the region, period, and climatic variable! For 1961-1990,
> say,
> > and for the European mainland, there will probably not be a problem. The
> > density of stations is sufficient that individual stations coming in
> and out
> > are not likely to substantially affect the values over this large area.
> > However, over central Africa this is probably not true.
> >
> > Climate change detection is a specialised subject. It demands either
> > individual station time-series, or carefully assembled (usually
> > low-resolution) grids. See Q4 of the FAQ.
> >
> >> > How
> >> > can it be used as input for environmental modelling if it is not
> >> > accurate enough to show real phenomona of change?
> >
> > The high-resolution grids do show "real phenomona of change". However,
> it is
> > not the long-term changes for which the grids are optimised; the grids are
> > optimised for high-resolution 'snapshots', month by month.
> >
> > Perhaps it would help if I gave an example of how the data-sets can be best
> > used in data-sparse regions.
> > 1. Constructing a trend at a grid-box is not a good idea, as we
> explained in
> > the Nature paper.
> > 2. It would be legitimate to use linear regression to compare (say) April
> > precip over a few grid-boxes (or perhaps even one grid-box if the data at
> > that box seems to warrant it) with some comparable areal (not point!!)
> > environmental index from 1981-2000, to derive an estimate of the
> > relationship between interannual variability in precip and interannual
> > variability in the environmental index.
> >
> >> > Where does this
> >> > leave all the previous publications from CRU on regional climate
> >> > change?
> >
> > Largely unchanged, as I see it. These high-resolution grids are our 'best
> > estimate' of the climate, at a high spatial resolution, in each month in
> > 1901-2000. Perhaps the risks of temporal inhomogeneities at the level of
> > individual grid-boxes could have been made clearer in the past - that is a
> > matter of judgement I guess. The coarser-scale grids produced by CRU, such
> > as Phil Jones' work, are not affected because they use different methods.
> >
> >> > 2. Over what scale do you consider it legitimate to make spatial
> >> > comparisons? Again, some of the publications show, for example, maps
> >> > of Africa with different climate anomalies over about 1000km. With
> >> > greater densities of met stations in Europe, is the spatial
> >> > resolution any better there?
> >
> > I find it hard to give a definitive answer, because the spatial scale over
> > which the climate information is temporally homogenous varies with region,
> > period, and climatic variable. My answer above provides some hints.
> >
> >> > I absolutely appreciate the problem of the changing input from met
> >> > stations through time - we face the same sorts of irregular
> >> > sequential data input from satellite sensors. And I equally
> >> > appreciate that interpolation must blur the differences between
> >> > neighbouring grid-boxes - but over what distance relative to the
> >> > spatial distribution of input met stations?
> >
> > This depends on the spatial scales over which different variables vary. See
> > the New et al (2000) paper for the precise values used.
> >
> >> > We are being asked again and again to analyse patterns and causes of
> >> > "emerging" diseases in many parts of the world, and we are really
> >> > concerned to make real sense of the subject, which involves having an
> >> > accurate idea of the degree of climate change within land masses the
> >> > size of Europe. I am myself about to send off a paper for a
> >> > conference proceedings concerned with tick-borne diseases in Europe.
> >> > I have no agenda at all - I am as happy to discover that there has
> >> > been, or has not been, any relevant climate change to account for the
> >> > variety of temporal and spatial patterns of disease change across
> >> > Europe, but I am desperately keen to get it right as a basis for
> >> > further work.
> >> >
> >> > Looking forward to a fruitful dialogue with you.
> >> >
> >> > Regards
> >> > Sarah
> >
> > Regards
> >
> > Tim
> >
> > PS if any co-authors cc'd want to comment, please feel free!
>
>Tim - worth distinguishing between two types of problems with the New et al.
>data set:
>
>(a) it is specifically *not* designed for climate change
>detection/attribution in the classic IPCC anthropogenic GHG context because
>for environmental simulation we wish to capture *all* the changes in
>regional/local climate whether or not an artefact of urban development or
>land use change (this is the exact *opposite* of data sets for GHG detection
>since all such datasets should remove such influences - there is a string of
>papers going back 10 years or more criticising CRU/Phil's work on these very
>grounds - urban heat/desertification influences, etc.).
>
>(b) a largely unrelated weakness in the dataset is the inhomogeneity
>introduced due to changing station coverage over time. And here you are
>right to point out that the "accuracy" depends on place, season, variable
>and scale of aggregation. Mark has some error grids I believe and
>publishing maps of # stations in interpolation range would help, but in the
>end the data set relaxes to 1961-90 in the absence of actual station
>anomalies. This is what you mean by space-optimised, but space-optimised
>inevitably implies it becomes inhomogenous over time (increasingly so as
>scales become smaller in data sparse areas).
>
>The other point worth advising people is if they really want to look at very
>local scale (certainly sub-grid-scale, but maybe even supra-grid scale in
>data poor areas) issues - whether trends or environmental modelling - then
>they would be best advised to approach GHCN (or CRU) for access to the
>underlying station data. Then of course, people need to pay attention to
>the credibility and homogeneity of individual station series, in itself not
>a trivial task and one that dozens of papers have been written about.
>
>Hope this helps - share these comments with Phil or whoever else is
>appropriate.
>
>Mike
>
>
>
>
>
>
>
>
>
>
> > ____________________________________
> > Dr. Tim Mitchell
> > Tyndall Centre for Climate Change Research
> >
> > email: t.mitchellatXYZxyz.ac.uk
> > web: [2]www.cru.uea.ac.uk/~timm/ <[3]http://www.cru.uea.ac.uk/~timm/>
> > phone: +44 (0)1603 59 3904
> > fax: +44 (0)1603 59 3901
> > post: Tyndall, ENV, UEA, Norwich, NR4 7TJ, UK
> > ____________________________________
>
>------ End of Forwarded Message
Prof. Phil Jones
Climatic Research Unit Telephone +44 (0) 1603 592090
School of Environmental Sciences Fax +44 (0) 1603 507784
University of East Anglia
Norwich Email p.jonesatXYZxyz.ac.uk
NR4 7TJ
UK
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------ End of Forwarded Message

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