From	Keith Briffa	Date	Tue Nov 4 09:42:07 1997
To	Tom Wigley
Subject	Re:
Tom please do. Actually I would be interested to know whether Malcolm mentioned these results to Dave as he was in Krasnoyarsk a few months ago when I showed this stuff. I will be over in New York in a few weeks to discuss with Ed the possibility of putting in an NSF/NERC proposal to look at the tree biomass change question. Also,the initial impetus to redo this stuff was as part of a NERC project we have running in colllaboration with Ian Woodward - i which we are inputting high resolution climate data to Dolly to assess the roll of such variability on carbon uptake cheers Keith At 02:54 PM 11/3/97 -0700, you wrote: >Keith, > >Malcolm Hughes was here on Friday to see Dave Schimel about precisely the >issue you raise. Dave wants to see if he can validate his ecosystem model >using tree ring data. Sounds as if you already have the data to do this. >Can I show your e-mail to Dave? > >Tom > >On Mon, 3 Nov 1997, Keith Briffa wrote: > >> >> Tom >> thanks for the info. Actually this is a chance for me to to mention that >> we have for the last few months at least, been reworking the idea of >> looking in the Schweingruber network data for evidence of increasing tree >> growth and hence ,potentially at least, evidence of changing tree(read >> biomass) uptake of carbon. >> The results are dramatic - not to say earth shattering because they >> demonstrate major time-dependent changes - but changes that are consistent >> in different areas of the network. We have regionalised over 350 site >> collections , each with ring width and density data , age-banded the data >> so that we look only at relative growth in similar ages of trees through >> time and recombined the standardisd curves to produce growth changes in >> each region. Basically growth is roughly constant (except for relatively >> small climate variablity forcing) from 1700 to about 1850. It then >> increases linearly by about up until about 1950 after which time young ( up >> to 50 year old) basal area explodes but older trees remain constant . The >> implication is a major increase in carbon uptake before the mid 20th >> century - temperatue no doubt partly to blame but much more likely to be >> nitrate/Co2 . Equally important though is the levelling off of carbon >> uptake in the later 20th century. This levelling is coincident with the >> start of a density decline - we have a paper coming out in Nature >> documenting the decline . In relative terms (i.e. by comparison with >> increasing summer temperatures) the decline is represented in the ring >> width and basal area data as a levelling off in the long-timescale inrease >> ( which you only see when you process the data as we have). The density >> data do not show the increase over and above what you expect from >> temperature forcing. >> I have been agonising for months that these results are not some >> statistical artifact of the analysis method but we can't see how. For just >> two species (spruce in the western U.S. Great Basin area and larch in >> eastern Siberia) we can push the method far enough to get an indication of >> much longer term growth changes ( from about 1400) and the results confirm >> a late 20th century apparent fertilization! The method requires >> standardizing (localized mean subtraction and standard deviation division) >> by species/age band so we reconstruct relative (e.g. per cent change) only . >> We have experimented with integrating the different signals in basal area >> and density(after extracting intra ring ring width and density data where >> available) within a 'flat mass' measure which shows a general late 20th >> century increase - but whether this incorporates a defensible relative >> waiting on the different components (and what the relative carbon >> components are) is debatable. We now need to make some horrible simplistic >> assumptions about absolute carbon in these (relatively small) components of >> the total biomass carbon pool and imlpications for terrestrial and total >> carbon fluxes over the last few hundred years - and beyond! Without these >> implications we will have difficulty convincing Nature that this work is >> mega important. >> There are problems with explaining and interpreting these data but they are >> by far the best produced for assessing large scale carbon-cycle-relevant >> vegetation changes - at least as regards well-dated continous trends. I >> will send you a couple of Figures ( a tiny sample of the literally hundreds >> we have) which illustrate some of this. I would appreciate your reaction. >> Obviously this stuff is very hush hush till I get a couple of papers >> written up on this. We are looking at a moisture sensive network of data at >> the moment to see if any similar results are produced when >> non-temperature-sensitive data are used. You would expect perhaps a greater >> effect in such data if Co2 acts on the water use efficiency . >> At 09:30 AM 11/3/97 -0700, you wrote: >> >Dear Keith, >> > >> >Look at Tremblay et al. GRL 24, 2027-30 (1997) and Dyke et al. Arctic 50, >> >1-16 (1997). These papers deal with driftwood in the Arctic over the past >> >9000 years. They note that genera can be distinguished, but not species >> >Hence, they can't say where the wood comes from, North America versus >> >Europe. Surely cross-dating could do this? May be worth getting in touch >> >with Dyke et al. >> > >> >Tom >> > >> -- >> Dr. Keith Briffa, Climatic Research Unit, University of East Anglia, >> Norwich, NR4 7TJ, United Kingdom >> Phone: +44-1603-592090 Fax: +44-1603-507784 >> > > > ********************************************************** > *Tom M.L. Wigley * > *Senior Scientist * > *National Center for Atmospheric Research * > *P.O. Box 3000 * > *Boulder, CO 80307-3000 * > *USA * > *Phone: 303-497-2690 * > *Fax: 303-497-2699 * > *E-mail: wigley@ucar.edu * > ********************************************************** > >