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Climate Models Not Up to Task of Resolving Cloud Microphysics Issues
Reference
Grabowski, W.W.  2000.  Cloud microphysics and the tropical climate: Cloud-resolving model perspective.  Journal of Climate 13: 2306-2322.

What was done
The author discusses the multiple roles played by cloud microphysics in determining tropical climate, using highly idealized cloud-resolving simulations to convey his perspective on the issue.

What was learned
The "fundamental question" addressed by the author is "to what extent cloud microphysical processes influence the climate of the tropical atmosphere."  As a result of his computational exercises, he concludes that "it is unlikely that traditional convection parameterizations can be used to address this fundamental question in an effective way."  Indeed, he notes that "classical convection parameterizations do not include realistic elements of cloud physics and they represent interactions among cloud physics, radiative processes, and surface processes within a very limited scope."  Consequently, he states the obvious when he says that "model results must be treated as qualitative rather than quantitative."  Furthermore, he notes that because ocean dynamics has to be considered as an essential part of the problem and because the temporal scales of ocean dynamics are at least two orders of magnitude longer than those of atmospheric dynamics, "understanding the relation between cloud physics and the tropical climate may be even more challenging than first thought."

What it means
Two verities stand out.  First, state-of-the-art climate models are still woefully inadequate for making quantitative predictions of surface air temperature response to atmospheric CO2 enrichment.  Second, it will be a very long time before this inadequacy can be overcome.


Reviewed 16 August 2000