Wednesday, December 21, 2011

1158204073.txt

From: Eystein Jansen <Eystein.Jansen@geo.uib.no>
To: Jonathan Overpeck <jto@u.arizona.edu>, David Rind <drind@giss.nasa.gov>
Subject: Re:
Date: Wed, 13 Sep 2006 23:21:13 +0200
Cc: Keith Briffa <k.briffa@uea.ac.uk>, rahmstorf@ozean-klima.de, Bette Otto-Bleisner <ottobli@ncar.ucar.edu>, cddhr@giss.nasa.gov, joos <joos@climate.unibe.ch>, Eystein Jansen <eystein.jansen@geo.uib.no>, "Ricardo Villalba" <ricardo@lab.cricyt.edu.ar>, t.osborn@uea.ac.uk

Hi all,

My take on this is similar to what Peck wrote. My suggestion is to write:

Greater uncertainty associated with proxy-based temperature estimates for individual years
means that it is more difficult to gauge the significance, or precedence, of the extreme
warm individual years observed in the recent instrumental record, such as 1998 and 2005,
in the context of the last millennium.

I think this is scientifically correct, and in essence means that we, as did the NAS panel
say, feel the TAR statement was not what we would have said. I sympatise with those who say
that it is not likely that any individual years were warmer, as Stefan has stated, but I
don�t think we have enough data to qualify this on the hemispheric mean.

Best wishes,

Eystein

If this is interpreted as a critisim of the TAR, then I think we

At 14:09 -0600 13-09-06, Jonathan Overpeck wrote:

thanks David - lets see what others think. I agree, that we don't want to be seen as
being too clever or defensive. Note however, that all the TAR said was "likely" the
warmest in the last 1000 years. Our chapter and figs (including 6.10) make it clear that
it is unlikely any multi-decadal period was as warm as the last 50 years. But, that
said, I do feel your are right that our team would not have said what the TAR said about
1998, and thus, we should delete that second sentence.

any other thoughts team?

thx, peck

Leaving aside for the moment the resolution issue, the statement should at least be
consistent with our figures. Fig. 6-10 looks like there were years around 1000 AD that
could have been just as warm - if one wants to make this statement, one needs to expand
the vertical scale in Fig. 6-10 to show that the current warm period is 'warmer'.

Now getting back to the resolution issue: given what we know about the ability to
reconstruct global or NH temperatures in the past - could we really in good conscience
say we have the precision from tree rings and the very sparse other data to make any
definitive statement of this nature (let alone accuracy)? While I appreciate the
cleverness of the second sentence, the problem is everybody will recognize that we are
'being clever' - at what point does one come out looking aggressively defensive?

I agree that leaving the first sentence as the only sentence suggests that one is
somehow doubting the significance of the recent warm years, which is probably not
something we want to do. What I would suggest is to forget about making 'one year'
assessments; what Fig. 6-10 shows is that the recent warm period is highly anomalous
with respect to the record of the last 1000 years. That would be what I think we can
safely conclude the last 1000 years really tells us.

David

At 9:10 AM -0600 9/13/06, Jonathan Overpeck wrote:

Keith - thanks for this and the earlier updates. Stefan is not around this week, but
hopefully the others on this email can weight in. My thoughts...

1) We MUST say something about individual years (and by extension the 1998 TAR
statement) - do we support it, or not, and why.

2) a paragraph would be nice, but I doubt we can do that, so..

3) I suggest putting the first sentence that Keith provides below as the last sentence,
in the last (summary) para of 6.6.1.1. To make a stand alone para seems like a bad way
to end the very meaty section.

4) I think the second sentence could be more controversial - I don't think our team
feels it is valid to say, as they did in TAR, that "It is also likely that, in the
Northern Hemisphere,... 1998 was the warmest year" in the last 1000 years. But, it you
think about it for a while, Keith has come up with a clever 2nd sentence (when you
insert "Northern Hemisphere" language as I suggest below). At first, my reaction was
leave it out, but it grows on you, especially if you acknowledge that many readers will
want more explicit prose on the 1998 (2005) issue.

Greater uncertainty associated with proxy-based temperature estimates for individual
years means that it is more difficult to gauge the significance, or precedence, of the
extreme warm years observed in the recent instrumental record. However, there is no new
evidence to challenge the statement made in the TAR that 1998 (or the subsequent
near-equivalent 2005) was likely the warmest of Northern Hemisphere year over the last
1000 years.

5) I strongly agree we can't add anything to the Exec Summary.

6) so, if no one disagrees or edits, I suggest we insert the above 2 sentences to end
the last (summary) para of 6.6.1.1. Or should we make it a separate, last para - see
point #3 above why I don't favor that idea as much. But, it's not a clear cut issue.

Thoughts? Thanks all, Peck

Eystein and Peck
I have thought about this and spent some time discussing it with Tim. I have come up
with the following

Greater uncertainty associated with proxy-based temperature estimates for individual
years means that it is more difficult to gauge the significance, or precedence, of the
extreme warm years observed in the recent instrumental record. However, there is no new
evidence to challenge the statement made in the TAR that 1998 (or the subsequent
near-equivalent 2005) was likely the warmest in the last 1000 years.

This should best go after the paragraph that concludes section 6.6.1.1
I believe we might best omit the second sentence of the suggested new paragraph - but
you might consider this too subtle (or negative) then. I think the second sentence is
very subtle also though - because it does not exclude the possibility that the same old
evidence that challenges the veracity of the TAR statement exists now , as then!
I think this could go in the text where suggested , but I think it best NOT to have a
bullet about this point.We need to check exactly what was saidin the TAR . Perhaps a
reference to the Academy Report could also be inserted here?
Anyway, you asked for a straw-man statement for all to argue about so I suggest we send
this to Stefan, David , Betty and whoever else you think.
cheers
Keith

--
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/

--

Jonathan T. Overpeck
Director, Institute for the Study of Planet Earth
Professor, Department of Geosciences
Professor, Department of Atmospheric Sciences
Mail and Fedex Address:
Institute for the Study of Planet Earth
715 N. Park Ave. 2nd Floor
University of Arizona
Tucson, AZ 85721
direct tel: +1 520 622-9065
fax: +1 520 792-8795
http://www.geo.arizona.edu/
http://www.ispe.arizona.edu/

--

///////////////////////////////////////////////////////////////////////////
///////////////////////////////////////////////////////////////////////////

--

Jonathan T. Overpeck
Director, Institute for the Study of Planet Earth
Professor, Department of Geosciences
Professor, Department of Atmospheric Sciences
Mail and Fedex Address:
Institute for the Study of Planet Earth
715 N. Park Ave. 2nd Floor
University of Arizona
Tucson, AZ 85721
direct tel: +1 520 622-9065
fax: +1 520 792-8795
http://www.geo.arizona.edu/
http://www.ispe.arizona.edu/

--

______________________________________________________________
Eystein Jansen
Professor/Director
Bjerknes Centre for Climate Research and
Dep. of Earth Science, Univ. of Bergen
All�gaten 55
N-5007 Bergen
NORWAY
e-mail: eystein.jansen@geo.uib.no
Phone: +47-55-583491 - Home: +47-55-910661
Fax: +47-55-584330

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