Cbacba,
The response I always see from the pro-anthropogenic global warming crowd on this issue is that the cooling trend was absolutely caused by aerosols. I am always amused when I see this one, because almost everywhere else (e.g., the WG 1 IPCC Summary for Policymakers), the same people say that we only have a low understanding of the aerosol forcing. So my question is, if we don’t understand the aerosol forcing, how can they be so sure this cooling trend was related to aerosols at all?
To take this argument to one logical conclusion, if aerosols are a more important climate forcing than CO2 (as would be implied by the cooling trend in question if you subscribe to the aerosols explanation), one quick fix for global warming might be to remove all the baghouses, ESPs, and SCRs from the power plants, thereby creating more aerosols to control the warming. (Increasing NOX and particulates could give you more aerosols without the sulfuric acid rain effects you would get by turning off the SO2 scrubbers. One concern would be increased ozone, but most ozone problems seem to be caused by automobiles and natural VOCs.) Of course, I am not advocating any of this. My real answer to your question would be that we still don’t have a solid understanding of why the climate does what it does.
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