cc: wg1-ar4-ch06@joss.ucar.edu date: Wed, 12 Jan 2005 12:40:03 +0100 from: Stefan Rahmstorf subject: Re: [Wg1-ar4-ch06] Bullet points for the executive summary for to: David Rind A response to David's comment on bullet point 6.2.3: this is not a bullet point that refers to any particular model, but to all efforts of modeling paleoclimate. Personally, I think that these efforts show encouraging successes. Now, if other people think that the efforts in modeling paleoclimate over the past years were mostly a failure, we may need to revise this bullet point. This could turn out to be a discussion over wether the glass is half full or half empty, though, which we may not resolve. The reason I wrote about "encouraging successes" is that many people have the impression that climate models are generally unable to reproduce past climate changes, and I think that's not true, I think we are starting to get some encouraging successes, while we are of course still in an early stage of this field. On the different models there is indeed a disagreement between David and myself, which partly reflects how in my perception the GCM community is attempting to hold back the competition from other models and retain an exclusive claim to the truth, so to speak. The term "first principle models" used by David is a case in point, it is a term chosen to make GCMs appear as "first principle", while other models are put into a class below that. I don't think this kind of language is helpful or can be justified in a scientific sense. To give an example: arguably the most severe simplification in the atmosphere model of CLIMBER2 is that synoptic eddies in the atmosphere are not resolved, rather their effects on the large-scale circulation are parameterised. To parameterise the effects of synoptic eddies is standard practice in all ocean GCMs used in coupled climate models. Hence, if using such a parameterisation of synoptic eddies makes a model not "first principle" any more, then none of the existing coupled GCMs is a "first principle" model either. What David calls "first principle" models employ many parameterisations that are not first principle - clouds, convection, you name it. Clearly there is a whole spectrum of models, and they use different ways of simulating and parameterising various mechanisms, which have to be evaluated on a case by case basis, and some models are better for some purposes than others. (Think of tsunami spreading models - the best models for that will use the shallow water equations rather than the primitive equations, and it would be silly to argue this is somehow bad or not state-of-the-art because it is a "simplified" model.) I would really object to any value-laden statements that suggest GCMs are somehow fundamentally different from models that parameterise or simplify one process or another. Cheers, Stefan -- Stefan Rahmstorf www.ozean-klima.de www.realclimate.org _______________________________________________ Wg1-ar4-ch06 mailing list Wg1-ar4-ch06@joss.ucar.edu http://www.joss.ucar.edu/mailman/listinfo/wg1-ar4-ch06