cc: gschmidt@giss.nasa.gov, mann@psu.edu, davet@atmos.colostate.edu, p.jones@uea.ac.uk, david.parker@metoffice.gov.uk, wpatzert@jpl.nasa.gov, ackerman@atmos.washington.edu, wallace@atmos.washington.edu, tbarnett-ul@ucsd.edu, sarachik@atmos.washington.edu, peter.thorne@metoffice.gov.uk, john.kennedy@metoffice.gof.uk, cwunsch@mit.edu 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 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 P. O. Box 3000, (303) 497 1318 Boulder, CO 80307 (303) 497 1333 (fax) Street address: 1850 Table Mesa Drive, Boulder, CO 80305