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To put it simply, if temperature change causes a change in the top-of-atmosphere radiative balance, then you can (with some assumptions regarding time lags) diagnose feedbacks by simply regressing the radiative variations against the temperature variations.BUT if it is instead a time-varying radiative imbalance causing a surface temperature change (causation reversed), .The downward sky infrared is consistent with the BSRN network measurements during the warm season.Note that the energy fluxes have to sum to zero for temperature equilibrium, and we will ignore the photosynthetic storage of energy in plants which is very inefficient.First, let’s examine some approximate energy fluxes for vegetation in the summertime.
These are only rough estimates, and there are rather large variations in these depending on cloud cover, etc., and to be meaningful they need to represent a day night average (infrared fluxes are orange; solar are yellow; convective are blue): For simplicity, the calculated IR emission from solid surfaces assumes an emissivity of 1.
Now, with a greenhouse in place, we assume the average temperature of the interior rises, and that the glass roof reaches a temperature intermediate between the inside and outside air temperatures: What really changes a lot is the downwelling IR, increasing from the sky value of 350 W/m2 to 450 W/m2, an increase of 100 W/m2.
Convective heat generated (but temporarily “trapped”) within the greenhouse increases substantially, from 208 without the roof to 275 with the roof, for an increase of 67, which further heats the air, which in turn is helping to heat up the roof.
There are many energy fluxes involved (I haven’t even addressed energy losses out the side of the greenhouse) and the trick is to know which are the important ones and which ones can be ignored for the purposes of a rough estimate.
For example, the emissivity of glass is less than 1, but what that means is that it “traps” even more IR energy inside because it partly reflects the higher levels of IR the warmer vegetation is emitting upward. I’m sure this problem has been analyzed before, probably in great detail, by multiple aggie graduates in their theses.
I’m open to ideas, and better estimates of energy fluxes on this subject.