A short lesson in simple logic

In his recent thread  ‘ A simple argument supporting a radiative greenhouse effect’,  Tim Folkerts opened with this statement:

This is about the simplest, most intuitive, most irrefutable argument I can come up with for why gases like CO2 and H20 in the atmosphere (“greenhouse gases”) must warm the surface.

He then goes on to attempt proofs of two propositions.

For a given surface temperature, less radiation leaves a world with cool greenhouse gases than a world with no greenhouse gases.

and

A warmer world with GHGs can radiate away the same energy as a cooler world with no GHGs.

However, neither of these support the assertion implicit in the opening statement, that “gases like CO2 and H20 in the atmosphere (“greenhouse gases”) must warm the surface.”

This is a common mode of argumentation from proponents of the radiative greenhouse theory. It contains a common logical error called non-sequitur (it does not follow) which negates it. To Illustrate this, consider the following propositions and the final deduction:

Phil owns a ball
Phil’s ball is red
This ball is red
Therefore this ball belongs to Phil

It’s easy to see that the deduction is a non sequitur. It is also indeterminate. It could be true, but we can’t tell from the available information whether or not it is true.

For the proposition to be true, there would need to be both necessary and sufficient conditions.
The necessary condition in this example is that the ball is red.
Sufficient conditions might be one of the following:

• All balls belong to Phil
• There is only one red ball

I’m sure you can think of a few more.

Getting back to climate science and Tim’s claim that “gases like CO2 and H20 in the atmosphere (“greenhouse gases”) must warm the surface”:
The point is that even if having radiatively active gases like co2 and water vapour is a necessary condition for the surface to have the potential to be warmer than the final emission-to-space temperature, it does not follow that it is a sufficient condition for the actuality of that higher temperature.

Just because Co2 and H2O cool the planet by radiating to space and this happens to open up the possibility for the surface to get warmer, it does not follow that it is the co2 and the H20 that do the warming. Indeed, there are several reasons why we might come to the conclusion that they can’t.

Radiative greenhouse proponents tend to react to this startling revelation in one of three ways.

They don’t comment further on that discussion thread.

or

They change the subject.

or

They reframe the argument.

This last one is the most interesting. One example goes like this:

But what else could it be?

(^tm Phil Jones)

As if leaving this question hanging in the air was somehow sufficient to win the day. The answer is of course:

Several other things.

.

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