cc: wg1-ar4-ch06@joss.ucar.edu
date: Wed, 20 Jul 2005 16:22:16 +0200
from: Stefan Rahmstorf <rahmstorf@ozean-klima.de>
subject: Re: [Wg1-ar4-ch06] Comments on Section 6.3
to: David Rind <drind@giss.nasa.gov>

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Dear David,

I take from your response that you consider all models that parameterise 
an important first-order process "conceptual models". I can live with 
that - but then there are only conceptual climate models around. Any 
coupled climate GCM that I know of parameterises oceanic convection (and 
in a very crude way), hence it is a conceptual model in your terms, and 
there is no fundamental distinction of category between your model and 
our model.

To me the scientific question is not whether an important process is 
parameterised (many are in GCMs) - it is how well this parameterisation 
works, for the task at hand. We have tested the feedbacks in great 
detail (e.g., the cloud, water vapour, lapse rate and snow/ice albedo 
feedbacks for 2xCO2) in our model and they perform quantitatively within 
the range simulated by various GCMs. The same is true for many other 
diagnostics - the model has taken part in model intercomparisons with 
GCMs and always falls within the range of different GCMs, in a 
quantitative way. To repeat that point, the quantitative differences 
between different GCMs are larger than the typical difference between 
our model and a GCM. So I see no basis for your claim that this model 
can only "suggest orders of magnitude". That's just plain wrong from all 
the evidence that I have seen (a lot). If you have concrete evidence to 
the contrary, other than just knowing one person who happens to agree 
with you, please come forward with it.

Stefan

-- 
To reach me directly please use: rahmstorf@ozean-klima.de
(My former addresses @pik-potsdam.de are read by my assistant Brigitta.)

Stefan Rahmstorf
www.ozean-klima.de
www.realclimate.org

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