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date: Mon, 07 Jul 2008 14:02:30 -0600
from: Kevin Trenberth <trenbert@ucar.edu>
subject: Re: clearing up climate trends sans ENSO and perhaps PDO?
to: Andrew Revkin <anrevk@nytimes.com>

   Andy
   The PDO is written up and some maps given in IPCC Chapter 3.  Most of it will already be
   accounted for in global T if  ENSO is accounted for.   You will see from Figure 3.28 that
   there is a strong PDO signature in the tropics that maps onto ENSO, even though it is
   derived entirely from extratropical SSTs.
   Given that this is supposed to be a decadal oscillation, all the stuff about a switch in
   PDO is utter nonsense and is simply aliasing of ENSO.  Exactly the same thing happened
   after the 1997-98 switch to a La Nina.  It is impossible to tell whether a switch has
   occurred or whether it is a single La Nina until many years after the event, by
   definition.
   In any case it is silly to "remove" the decadal variability because that is the signal and
   the question is whether this is a manifestation of global warming or not?  As we note in
   IPCC, there are aspects of this that are NOT decadal variability but rather constitute a
   singular event (see Fig 3.29) and there is no sign that it is not part of the trend or
   actually a step function to a different way for climate to operate.  This is not simulated
   by climate models, but that is likely a problem with models.   The information to date
   suggests the PDO and the 1976/77 step function originates in the tropics and involves the
   Indian ocean as well the Pacific.
   Please see the IPCC Chapter 3.
   Kevin
   Andrew Revkin wrote:

   dear all,

   re-sending because of a glitch.

   finally got round to posting on an earlier inquiry I made to some of you about whether
   there was a 'clean' graph of multi-decades temperature trends with ENSO wiggles removed --
   thanks to gavin (and david thompson) posting on realclimate.

   here's Dot Earth piece with link to Realclimate etc..

   [1]http://dotearth.blogs.nytimes.com/2008/07/07/climate-trends-with-some-noise-removed/?ex=
   1216094400&en=a57177d93165cba3&ei=5070

   next step is PDO. has anyone characterized how much impact (if any) PDO has on hemispheric
   or global temp trends, and if so is there a graph showing what happens when that's
   accounted for?

   as you are doubtless aware, this is another bone of contention with a lot of the
   anti-greenhouse-limits folks and some scientists (the post 1970s change is a PDO thing, etc
   etc). hoping to show a bit of how that works.

   thanks for any insights.

   and i encourage you to comment and provide links etc with the current post to add context
   etc.

--

   Andrew C. Revkin
   The New York Times / Science
   620 Eighth Ave., NY, NY 10018
   Tel: 212-556-7326 Mob: 914-441-5556
   Fax:  509-357-0965

   [2]www.nytimes.com/revkin

--
****************
Kevin E. Trenberth                  e-mail: [3]trenbert@ucar.edu
Climate Analysis Section,           [4]www.cgd.ucar.edu/cas/trenbert.html
NCAR
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