cc: trenbert@ucar.edu, tom.delworth@noaa.gov, broccoli@envsci.rutgers.edu, cwunsch@ocean.mit.edu, rcurry@whoi.edu, jseveringhaus@ucsd.edu, shs@stanford.edu
date: Wed Apr 30 09:57:37 2008
from: Phil Jones <p.jones@uea.ac.uk>
subject: Re: nature paper / ocean model as short-term regional climate
to: Stefan Rahmstorf <rahmstorf@ozean-klima.de>, Andrew Revkin <anrevk@nytimes.com>

    Andy,
       You raise an interesting issue. We've all heard the comment, why should I believe
    in climate change when the weather forecasts can be shown to be wrong some of the
    time. The forecasts in this paper take this type of question a stage further. As Stefan
   says
    they are very much 'work in progress' and they are attempting to get to more policy
   relevant
    timescales of the next 20 years. Their success or not, though, will likely influence how
    govts and the public might respond to the need for more Kyoto type reductions in the next
    few years. Maybe they will not have much of an effect as memories appear to be getting
    shorter. As more centres move into this area, we will get more of a feel of how good
    they might be. They are still only of average conditions, and peoples views of a 'winter'
   or
    a 'summer' are normally swayed by a few weeks within the season.
        You mention the post-98 warming slowdown as seeming to be real. Watch out for
    a paper you'll get from Nature in the w/o May 29. I'll be in my office that week.
         An aside, but I've noticed over the past year or so, when I occasionally discuss
    what I do with fellow travellers on planes. I say I'm a climatologist - reply is often,
    that's interesting do you believe in climate change? Maybe this is people just making
    conversation, but it comes across to me the same as do you believe in God or evolution,
    as though climate change is a bit like a religion. My general riposte is to tell people to
   look
    around them and see the changes (in Europe) - in the earlier spring season, the
    lack of snow/frosts etc.
      Cheers
    Phil
   At 11:09 29/04/2008, Stefan Rahmstorf wrote:

     Dear Andy,
     thanks for asking. I think this an interesting paper and this kind of decadal
     forecasting will become increasingly important. On the other hand, it is still early
     days, this is pioneering work and many aspects of this are not yet properly understood,
     as Richard Wood rightly cautions in his N&V. Not least, nobody knows what the MOC really
     has done over the past decades.
     So what does this mean for the forecasts?
     The prediction of European cooling: I'd take that in a Bayesian sense as some evidence
     for possibly cooler temperatures, but not enough to make cooling more likely than
     warming for me. So if I had to bet money at equal odds on warming or cooling, I'd still
     bet on warming, although with less confidence than previously. I'm not sure their error
     bars give the full error - note for example that their forecast error bar for 2015 in
     Fig. 4 is almost zero, so even without having had time to properly look at what this
     error bar encompasses, I suspect that it is not the full uncertainty. And of course they
     predicted the 1994-2004 period to be quite a bit cooler than before, and it turned out
     to be warmer (Fig. 3c).
     Prediction of global temperature: The authors claim that this "may not increase over the
     next decade". However, their standard A1B run has a higher correlation with global
     temperature than their hindcast run, and their hindcast run predicted cooling over the
     past 5 years (the period 1994-2004 was hindcast as being colder than the decade centered
     five years earlier) when in fact warming happened, and it predicted flat global
     temperatures in the past 10 years (in this sense) when warming occurred.
     This is very interesting when you compare it to the time evolution of the MOC. Almost
     the entire verification period, where their method shows some skill, the MOC has been
     increasing. Since about 1990 it has stopped to increase and started to decrease (in
     their analysis, nobody knows for real), and consequently their method predicts cooling
     over Europe and globally since then - but up until now, for the past two points in their
     series, this prediction turned out to be wrong. That's why I'm not sure whether I
     believe it for their next two points. If the method works only while the MOC is
     increasing, but not while it is decreasing - maybe the past forecast skill has nothing
     to do with the MOC? Certainly it has not been well-validated for times of decreasing
     MOC. They predicted a slight cooling for Europe for 1965 and 1970, but the observed
     trends here are closer to the scenario run without the MOC forecast. The early phase of
     weak diagnosed MOC, before 1970, may also not be weak MOC at all (according to some work
     by Mike Mann), it may be at least partly an effect of aerosol cooling over the North
     Atlantic region, which has the effect of cooling regional SST and thereby looking like
     weak MOC - it would be hard to disentangle the two effects.
     So I think this is good work, I do not want to denigrate this in any way, but as I said
     it is very early days with this type of forecasting and many questions are still not
     properly understood, so I would not start to draw strong conclusions at this point. Of
     course the basic message is always correct: some natural variability is always
     superimposed on the greenhouse warming trend, so ten years of less warming or more
     warming don't tell us anything about this greenhouse trend - see the discussion we had
     on realclimate on this point:
     [1]http://www.realclimate.org/index.php/archives/2008/01/uncertainty-noise-and-the-art-o
     f-model-data-comparison/
     You could test how serious the authors are: tell them that a prominent climatologist is
     offering them a bet of $10,000 at equal odds that global mean temperature will be
     warming over the next decade. Are they prepared to bet against this?
     Cheers, Stefan
     --
     Stefan Rahmstorf
     [2]www.ozean-klima.de
     [3]www.realclimate.org

   Prof. Phil Jones
   Climatic Research Unit        Telephone +44 (0) 1603 592090
   School of Environmental Sciences    Fax +44 (0) 1603 507784
   University of East Anglia
   Norwich                          Email    p.jones@uea.ac.uk
   NR4 7TJ
   UK
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