Dear Andy,
I find this exchange a little peculiar in that you never seem to address what I understand Roy's main points to be.
First, Roy notes that outgoing radiation (especially in the visible) varies for many reasons of which feedback to surface temperature is but one. Other obvious examples range from volcanic aerosol production to cloud triggering by Kelvin-Helmholtz instabilities. I know of no one who really questions that surface temperature is not the only or even the main source of fluctuations in visible radiation.
Second, any changes in outgoing radiation will also cause changes in surface temperature. This is simply a matter of elementary thermodynamics. For non-feedback changes in radiation, the temperature changes will follow rather than lead temperature changes.
Third, because of the first two points, simple regressions of outgoing radiation on surface temperature will not be a useful measure of feedback. Spencer and Braswell illustrated this in their paper. There are, of course, other problems with the use of simple regressions as well.
It would be interesting to see your response to these points.
Best wishes,
Dick
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