Thursday, June 7, 2012

4942.txt

date: Tue, 14 Feb 2006 09:58:18 +0000
from: Martin Juckes <m.n.juckesatXYZxyzac.uk>
subject: Re: Draft conclusions for report to Netherlands Environment
to: Keith Briffa <k.briffaatXYZxyz.ac.uk>

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/
>
>
>

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