date: Tue, 14 Feb 2006 09:58:18 +0000 from: Martin Juckes subject: Re: Draft conclusions for report to Netherlands Environment to: Keith Briffa Kieth, thanks for those comments, I'll adjust the text. On the Medieval Warm Period: I was thinking of a statement in Jones et al. (1998), but what they actually said was that "their is little evidence for the Medieval Warm Period" -- so I suppose we should say that since then a bit more evidence for a modest warm anomaly has emerged. cheers, Martin On Monday 13 Feb 2006 16:03, you wrote: > Martin > been through this and please see my comments in square brackets. > > Really am trying to get to the other stuff. > Keith > At 16:32 09/02/2006, you wrote: > > >Hello, > > > >I need to send in a draft report to RIVM soon. The summary should lay out > >what we believe to be the state of knowledge on temperatures in the > >last millenium. > > > >I would be grateful for feedback on the text below. > > > >regards, > >Martin > > > > > >Summary > > > >IPCC (2001) concluded that ``The 1990s are likely to have been the > >warmest decade of the millennium in > >the Northern Hemisphere, and 1998 is likely to have been the warmest > >year," where ``likely'' implies a greater than 66\% probability > >[this implied a confidence level of between 66 and 95%] > >(this conclusion will be referred to below as ``C1''). > >The Northern Hemisphere temperatures are believed to have shown a > >gradual cooling trend from the start of the millenium until the > >mid 19th century, and a warming trend since then. Substantial > >interannual, decadal and centennial scale variability was superimposed > >on these trends. > > [In the Tar the focus was on Mannet al 1998,1999 and they did not > show what I would call "substantial centennial" variability] > > > The warming trend contains a signifcant natural component, > >but an anthropogenic contribution was clearly detectable towards the > >end of the 20th century. > > > >This conclusion was based on a wide range of results, > >including that of Mann et al., (1999). > >Since publication of the IPCC (2001) report there has been much criticism of > >the techniques used to estimate temperatures, particularly those > >used by Mann et al. > >The criticism of the latter work has drwan [drawn] attention to incomplete > >documentation of the wide range of data sources used and to incomplete > >description of some aspects of the analysis algorithm. > > [The situation has not been helped by the dis-information spread by > certain sceptics , however, that in my opinion act deliberately to > confuse the issue] > > >The debate has attracted much public interest and generated > >considerable confusion. > > > >(C1) is sometimes paraphrased as ``there was no hemispheric wide > >Medieval Warm Period'', but this > >terminology leads to confusion: there is no agreed definition of > >what would constitute > >a `` Medieval Warm Period''. > > [Actually Martin I do not believe anyone says or believes that there > was NO medieval warm period - merely that it > is time transgressive , spatially poorly documented and , as you > imply, not precisely defined or quantified. There > was a period of relative warmth , but the question is how warm and > when (actually that is two questions!). ] > > > >A second conclusion of the IPCC report, which is related to but > >distinct from (C1), is > >that current temperature trends have a signifcant anthropogenic > >component (referred to as ``C2'' below). > > > >Conclusion (C2) is based mainly on GCM simulations and is not > >directly addressed in this > >study. Conclusion (C1) is based mainly on > >the interpretation of proxy climate records: this is the specific > >issue addressed here. Reconstructions of past climates are also used > >to evaluate > >GCM simulations of those climates and hence to evaluate the GCMs: > >this provides some > >indirect input into conclusion (C2). > > > >The following concpetual [conceptual] model can help us > >to understand how studies of the past millenium can contribute to > >discussion of future climate change: > > > > Temperature anomaly- = [ ( climate sensitivity-) times ( sum of forcings-) ] > > plus ( natural variability-) > > > >This is a drastic simplification: the different ``forcings'' (solar > >variability, > >volcanic and other natural changes to atmospheric composition, > >anthropogenic changes > >to atmospheric composition) can not be wholly characterised by a > >single number: > >their influcence on the climate system is extremely complex and the response > >of the climate is neither instantaneous nor uniform. Nevertheless, > >scientists have found > >this simple conceptual model to be a useful basis for discussion. > > > >By testing the models > >against observed climate variability it can be dtermiend > >[determined] whether they > >have a climate sensitivity which is realistic. The problem is that > >the period of reliable, > >global measurements is too short to carry out this exercise comprehensively. > > [this begs the fascinating question of constitutes "realistic" > climate sensitivity - given the problems > in defining the concept to account for transience on different > timescales - but your summary is good] > > >In the last 5 years a number of studies using different techniques > >and different, > >though overlapping [suggest say something like "using some common > >input data" rather than use the word "overlapping"], data > >collections have re-inforced (C1), though they > >disagree, both with Mann et al. and among themselves, on other issues. In > >particular, there is a relatively wide range of estimates as to the magnitude > >of the cold anomaly in the 18th century (during the ``Little Ice Age''). > > > > >[larger difference related to the cold of the 13th and 14th centuries] > > > > >It is clear that regional temperature anomalies can be much larger than > >those on the hemispheric scale. IPCC (2001) did not suggest that > >current temperattures are above the extremes experienced by > >any region in the past thousand years. Recent modelling work has > >led to greater understanding of climate variability on different > >scales. A lot of discussion in the popular and electronic media, > >and also, to a limited extent, in the peer reviewed literature, > >neglects this crucial distinction between what is happening on the global > >and regional scales. [agree wholeheartedly] > > > >Data centres have improved the transparency with which data is [are] > >available and the > >quality of the information accompanying the data, recording its provenance has > >also improved. > > > >The use of a wide range of different data sources and different > >analysis techniques > >makes evaluation of the differences among published results difficult. > >Within this project we have subjected data collections from a variety of > >authors to several analysis techniques. > >It is found that the range of different results is still spanned by the > >results when a single analysis technique is used. > >This suggests that a priority for further work to reduce the uncertainty > >will be to improve understanding of the data. > > > > > -- > Professor Keith Briffa, > Climatic Research Unit > University of East Anglia > Norwich, NR4 7TJ, U.K. > > Phone: +44-1603-593909 > Fax: +44-1603-507784 > > http://www.cru.uea.ac.uk/cru/people/briffa/ > > >