cc: calvert@unixg.ubc.ca (Steve Calvert), weaver@ocean.seos.uvic.ca date: Thu Aug 5 12:07:07 1999 from: Keith Briffa subject: Re: Skeptics to: Tom Pedersen , rbradley@climate1.geo.umass.edu Tom et al I agree with Mike that Hoyt's text is the usual mixture of selective , often mis- ,information that one could waste a lot of time on and end up only justifying it by virtue of seeming to take it too seriously. The depressing point is that this sort of abbreviated , semi-slick and seemingly objective presentation is accepted too readily by many people as convincing evidence against an enhanced greenhouse effect. There are problems with instrumental coverage but he makes no mention of the excellent paper by Jones et al (1997) in the Journal of Climate(Vol.10,2548-2568) that addresses the coverage issue directly and comprehensively and calculates realistic uncertainty values for Hemispheric and global average temperatures- showing mean temperatures in the last two decades to be unprecidentedly warm since the 1850s. He also ignores the papers that have compared urban and rural temperatures and concluded only a small urbanisation effect is contained in the Jones data. As for the proxy data he cites only tree-ring data when there are many more , and assumes a ubiquitous CO2 fertilisation effect in the tree-ring data used. This is a complex and unresolved issue which is done no justice by such simplistic and self-serving treatment. To answer Tom's question first, no, we have not corrected any of our reconstructions for an explicit fertilization ( CO2 or nitrate ) effect - simply because there is no theoretical basis for such a correction. Some tree-ring-based reconstructions may have moderated the expression of such an effect in recent data ( were it to exist) by the way the data have been temporally detrended in an attempt to remove better understood age-related effects in raw sample measurements. I believe some ringwidth series may have some fertilisation bias manifest as higher growth in recent decades but it is by no means definite and would be small . Temperature reconstructions based on ring density have an opposite bias - reduced density in recent years that may similarly be expressed to different degrees depending on the method of data processing and which would in any case suppress evidence of recent warming. This may or may not be associated directly with the effects of CO2 or other fertilization. Our density reconstructions still show the 20th century to be anomalously warm in a several hundred year context , and perhaps much longer one. The problem here is a genuine paucity of long series and statistical problems in processing and calibrating such data. We need to and are, doing much more work to explore these questions and Hoyt's simplistic statement about borehole data reflecting only temperature forcing simply shows a naive at best and dishonest at worst attitude to the many problems that afflict these , and all ,palaeodata. I for one still believe that we are seeing the manifestation of greenhouse warming but I know the evidence presented todate leves many questions still unanswered . I too believe that solar variabilty is a potential forcing factor that has likely contributed to the variability of 19th and 20th century observations . The extent of the effect surely requires much more model-based research. Simply correlating Hoyt's series against observations or reconstructed temperatures does not get us far. I also believe we have major uncertainty surrounding global or hemispheric estimates of centennial or millennial reconstructions , and real problems with spacial patterns on long timescales. Saying this does not make me an outlaw in the palaeo family - I hope! - just someone anxious to maintain our objectivity. We should all resist the attempts of those who try to push us into the pro or anti greenhouse camps. I think Hoyt's comments betray someone who is perhaps lacking the degree of objectivity I had previously thought him to have. At 01:36 PM 8/3/99 -0700, Tom Pedersen wrote: >Hi Ray: >My colleague, Steve Calvert, has just brought to my attention a website of >which I was unaware but you probably know well. It's at >http://www.erols.com/dhoyt1 >and run by Doug Hoyt. >Amongst other things Hoyt has taken the Mann reconstruction and >reconstructed it by "removing the effect on tree ring thickness that >results from CO2 fertilization" (paraphrased). You will see the figure on >his site. He concludes that there is no significant warming in the last >half of this century relative to the last millenium. Do you know this guy? >Are you familiar with his reconstruction of your reconstruction? Didn't >Keith Briffa correct his tree-ring reconstructions for CO2 fertilization? >[Keith: any comments?]. Steve and I would be most interested to hear your >collective comments... > >To close this, here is a bit cut and pasted from Hoyt's sight: > > > Three Final Points > >There are three important points to make about the reported warming of the >last 20 years: > >1. The warming has occurred mostly at night and not during the day. This >result is inconsistent with a warming >caused by greenhouse gases, but is consistent with urban heat island and >other surface effects. > >2. The reported warming has occurred only at the surface and not in the >upper atmosphere. This type of warming is >completely opposite to what is predicted if greenhouse gases are the cause. >Again these observations are consistent >with problems in the surface measurements. > >3. The warming has occurred primarily in the Northern Hemisphere >mid-latitudes with little in the polar and tropical >regions. This result is consistent with urban influences, but is >incompatible with the climate warming predicted from >greenhouse gases which predict it to be largest in the polar regions. > >In short, the reported warming is inconsistent with warming due to >greenhouse gases in its temporal, vertical, and >geographical distribution. The reported warming is consistent with problems >in the surface network. > > >Cheers, Tom > > >T.F. Pedersen >Oceanography, Earth and Ocean Sciences, 6270 University Boulevard, >University of British Columbia, Vancouver, B.C. Canada V6T 1Z4 >Telephone: 604-822-5984 Fax: 604-822-6091 Email: pedersen@eos.ubc.ca >http://www.eos.ubc.ca/ >