date: Mon Jul 18 14:25:52 2005
from: Phil Jones <p.jonesatXYZxyz.ac.uk>
subject: Re: Text and CQ stuff
to: "Parker, David (Met Office)" <david.parkeratXYZxyzoffice.gov.uk>, Kevin Trenberth <trenbertatXYZxyzr.edu>
Even without smoothing it is possible to get a trend of nearer 0.75 if the trend
starts around 1920 (especially if the cold year of 1917 is at the start). The
periods chosen for Table 3.2.2 had some justification, so we need to be a
little careful. As a schematic for CQ2 though, it will be a different way of
showing the same data.
I'll talk it over with David.
At 14:03 18/07/2005, Parker, David (Met Office) wrote:
I will discuss with Phil when he comes. We could ask John Kennedy to do
a plot. However, sub-period linear trends are already in Table 3.2.2
and, despite not being matched exactly to the sub-periods you suggest,
lead to a similar conclusion (ca 0.75C warming overall).
On Sat, 2005-07-16 at 22:59, Kevin Trenberth wrote:
> Hi all
> I have started going thru the text a bit more thoroughly. At present
> the description of the global mean temperature record is for a warming
> of 0.6C during the 20th Century. That is the linear reprducible
> value. But it is not a useful value as the trend is not linear. In
> the recent paper by Raper et al on SST they make a point to give
> values for both the linear trend and the change from the low pass
> filtered record. The latter is quite a bit bigger. I would like to
> see us adopt something similar. The question then is how to
> characterise the record. Here is my attempt: words
> However, the record is best characterized as level prior to about
> 1920, a warming to 1940 or so, leveling out or even slightly
> decreasing until 1970, and a fairly linear trend since then. Going by
> the low pass filtered data, the overall warming through 2005is 0.75ºC,
> with 0.5ºC increase occurring after 1970.
> To illustrate this I tried to capture the sense of this in the
> accompanying ppt. There are two slides. Make sure you go into slide
> show mode to view them. You will see the first has a smoothed trend
> the second has linear segments that join. The idea is to also capture
> the overall error bars to a reasonable degree, as you can see. In
> fact this could be linked to the modeling and attribution chapter to
> say that the warming in the first part of the 20th century was partly
> due to solar, the cooling from 1940 to 1970 to increased aerosol, and
> the warming after 1970 to the increasing GHGs.
> This could work very well as part of the CQ2.
> Ideally the background global mean values should not have the red bars
> on it but should just be a time series with error bars. The curves
> which I fitted by eyeball using power point should be done more
> rigorously, perhaps using a cubic spline fit with strong tension., or
> a series of segments with divides at 1940 and 1970. Then a linear
> value with the given starting point could be determined for both the
> mean and both end of the error bars.
> I am seeking feedback on this idea. 1) Is it a good idea and has your
> support? 2) Any comments or suggestions?
> 3) Any volunteers to do it more rigorously? Any such person would
> need the mean and error bars to do this from David or Phil?
> 4) Do you prefer the straight lines or smoothed values?
> Kevin E. Trenberth e-mail: trenbertatXYZxyzr.edu
> Climate Analysis Section, NCAR www.cgd.ucar.edu/cas/
> P. O. Box 3000, (303) 497 1318
> Boulder, CO 80307 (303) 497 1333 (fax)
> Street address: 1850 Table Mesa Drive, Boulder, CO 80303
David E Parker
A2_W052 Met Office FitzRoy Road EXETER EX1 3PB UK
Tel: +44-1392-886649 Fax: +44-1392-885681
Global climate data sets are available from http://hadobs.org
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