When looking at the radiative forcing equation for CO2, what is the coefficient alpha?

Question

Equation can be found here:

http://en.wikipedia.org/wiki/Radiative_forcing

Before anyone gets after me for using Wiki, this comes directly from:

Geophysical Research Letters, Vol 25, No. 14, pp 2715-2718, 1998

I ask because I am interested in knowing what they are trying to account for by the use of this coefficient in the equation.

Does this co-efficient account for the less than 100% absortion efficiency of CO2? Does it account for non-radiative relaxation processes, such as collisional relaxation? etc.

Trevor-->

AS far as I can tell, it isn't Cronbachs alpha. It looks like a fudge factor of some sort, and I want to know what they are considering in the fudge factor.

Keith-->

What factors go into this constant? How was it determined?

Grizz-->

How do they arrive at the number value for alpha? What factors went into determining it? Experimental? Modelling?

Answer 1

Alpha is related to the radiative efficiency. Different gasses reflect more or less heat than CO2. The fudge factor is different for each gas: 5.35 is not a constant, it is just the value for CO2.

The alpha value just allows apples to be compared with oranges, it allows the "effect" of different gasses to be compared to a standard value, e.g. if "air" reflects 1 unit of heat, the same quantity of CO2 reflects 5.35 units of heat.

Answer 2

There is no Cronbach's Alpha in the equation and neither should there be. Cronbach's α is a measurement of testing consistency and in this repsect is a forumla outwith the RF equation in much the same way as other consistency estimates such as SD or PE are.

Cronbach's α could be applied in so much as RF can be considered norm-referenced. The variance in the RF equation is small and consequently Cronbach's α will be high, I haven't run the numbers but would estimate about 0.98.

It also depends on the definition of RF that you're using - there's a general definition in much wider use than the technical scientific one. The general definition relies simply on calculating the difference between incoming solar radiation and outgoing thermal radiation, both of which can be measure to three point accuracy (in W/m2/yr) thus Cronbach's α will be almost 1.

The more scientific definition of RF is “The radiative forcing of the surface-troposphere system due to the perturbation in or the introduction of an agent is the change in net irradiance (solar plus long-wave measured in Watts per square metre per year) at the tropopause after allowing for stratospheric temperatures to readjust to radiative equilibrium but with surface and tropospheric temperatures and state held fixed at the unperturbed values”. Running with this introduces more variables into the equation, by and large these variables tend to the mean so Cronbach's α remains high.

Answer 3

Unless you can find a free copy of Gunnar Myre's work, it looks like you're going to have to pony up $9.

http://www.agu.org/pubs/crossref/1998/98GL01908.shtml

Personally, I'm not interested in any research that totally discounts radiative forcing due to water vapor.

Answer 4

The coefficient alpha is 5.35, and has now been updated in wikipedia. Nice catch.