cc: D Parker D Parker , John Mitchell John Mitchell , k.briffa@uea.ac.uk date: Tue, 23 Jun 1998 22:49:49 +0100 from: sfbtett@meto.gov.uk subject: Re: Draft Report on Detection Workshop (March 1998, Bracknell) to: Phil Jones Phil Jones Hi Phil, thanks for your comments -- almost missed including them (my fault) but here they are. Thanks for taking the time to read and comment on the report. Below is my response to your and Keith's comments. Phil Jones wrote: > > Simon, > Here are some comments from Keith and me. > > Background 1.1 > Should the 3rd paragraph include that the program also needs > longer climatic datasets to estimate longer timescale variability ? Yes -- added a sentence saying "Homogeneous observations of climate greater than 50 years would allow better comparison of model simulated variability with observed variability." -- sound OK? > Page 6 #4 > > Rewritten as : > > The reasons for the poor comparison between many proxy data > sources and temperature measurements should be explored with a > view to improving the proxy data. The development and expansion > of existing datasets of tree-ring density and tree-ring width > should be continued and these data made easily available to > the scientific community in order to allow validation of model > variability. OK -- included the 2nd sentence (1st sentence is what we have already) I note the addition of the word "expansion" -- John you happy with this? > Summaries of talks > > Mine : David sent some - here are some more > > Since 1900 the land surface temperature network shows large > changes in coverage. A network of about 1000 stations whose > records are homogeneous is sufficient to monitor regional-to- > global scale temperatures. The network needs to be maintained > and should be improved. Both these should be achieved as a > result of the initiative of GCOS (the GCOS surface network). > The 'Urbanization' contribution to warming over the twentieth > century is 0.05K, which is an order of magnitude smaller than > the observed warming. Sea surface temperature (SST) data is easier > to correct for changes in the observing system than the land > surface data as it can be calibrated against the night marine air > temperature and coastal land surface temperature measurements. > The five warmest years have all occurred during the 1990s. The > standard error of estimate of annual-mean global-mean temperature > is approximately 0.05K. Over the last 50 years diurnal temperature > range has decreased. A detection study using this variable may be > worth undertaking. OK -- made those changes > David has sent me some improvements to his piece on U/A datasets > which I agree with. > > Keith's talk > > Tree-ring width and tree-ring density measurements are a good > proxy for surface temperatures on timescales of 1 to 100 years. > On timescales beyond 100 years the results are often affected by > the removal of biological factors related to tree aging. Research is > currently being undertaken to extend the climate information > recoverable on longer timescales. Dating is very good for these > data sources. However, post-1950 they may contain significant > anthropogenic effects, which need to be removed. Other proxy data > sources such as corals and ice cores have great potential for > representing tropical and polar/high elevation regions but are > presently less certain in terms of dating and further work in > formal calibration with climatic data is desirable. Um, I thought that a fair summary of Keith's talk was that the Proxy data was really bad -- I think that does need to be said. How about, for the last sentence: "Other proxy data sources such as corals and ice cores have great potential for representing tropical and polar/high elevation regions but are currently unreliable as measures of surface temperature. This may be because the dating of them is less certain than tree ring proxies, and further work in formal calibration of these proxies with climatic data is needed." Simon Attachment Converted: "c:\eudora\attach\vcard1.vcf"