Thursday, June 7, 2012


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

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
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.
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..


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


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


Kevin E. Trenberth e-mail: [3]
Climate Analysis Section, [4]
P. O. Box 3000, (303) 497 1318
Boulder, CO 80307 (303) 497 1333 (fax)

Street address: 1850 Table Mesa Drive, Boulder, CO 80305

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