East Anglia Confirmed Emails from the Climate Research Unit - 1105730627.txt

From: David Rind <drind@xxxxxxxxx.xxx>
To: Stefan Rahmstorf <rahmstorf@xxxxxxxxx.xxx>
Subject: Re: 6.5.8 on climate sensitivity and last millennium
Date: Fri, 14 Jan 2005 14:23:47 -0500
Cc: David Rind <drind@xxxxxxxxx.xxx>, Tim Osborn <t.osborn@xxxxxxxxx.xxx>, Jonathan Overpeck <jto@u.arizona.edu>, Keith Briffa <k.briffa@xxxxxxxxx.xxx>, Eystein Jansen <eystein.jansen@xxxxxxxxx.xxx>, FortunatJoos@xxxxxxxxx.xxx

Here are my responses to the comments concerning 6.5.8d. With respect to Stefan's main
concern: I too am sensitive to the possible mis-use of words that appear in a cavalier
manner in the text. I think the way to avoid that is to be as precise as possible about
what is being said. I also feel that hand-waving should be minimized - just because there
are uncertainties, does not mean IPCC will throw up its hands. Thus the attempt to quantify
these numbers are precisely as they will be done in other IPCC chapters. Again, the
responses are in red, and the text alterations (or in this case, some entire text) are in
blue.

I'm not working on this topic myself so I'm by no means an expert. But I am still quite
concerned with the wording in 6.5.8 on the last millennium.
First, to avoid misunderstandings, I would like to suggest again to describe forcings
and climate changes going forward in time, rather than going backwards in time. Even
colleagues here that I discuss it with misunderstand the present version with backwards
reasoning - it leads to phrases like "deforestation warming" (used by David in his last
mail), although deforestation caused cooling - backwards in time you can see this as a
warming, but should you call it "afforestation warming" if you look back in time? I
suggest to use the physical, forwards, time arrow in the discussion.

In all the other sections of 6.5.8 we discuss the temperature change and the radiative
forcing relative to the present - when it was colder than the present, the temperatures
were indicated to be colder, and the radiative forcing more negative. To alter that for
this section alone would cause added confusion. I have therefore in each case tried to make
it perfectly clear what is being said. In particular, I agree that in the case of
deforestation the terminology does become confusing so the text has been changed to be more
communicative; it now reads,

Warming of 0.35

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