Falsifying AGW Theory

James Annan and Roger Pielke [James neglects to provide a link or even identify which RP is in question] are duking it out on the subject of falsifying the Anthropogenic Global Warming theory. If we are good Popperians, we should believe that a good scientific theory ought to be falsifiable - subject to disproof through predictions that fail to occur. General relativity, for example, would have been falsified if Einstein's predictions for the precession of Mercury's orbit and the the deflection of starlight during eclipses had proven wrong. Darwin's theory of natural selection would similarly have been damaged if the mechanisms of heredity had turned out to be different for each diffent type of animal.

So what are the critical observations for AGW, asks Roger? At the risk of oversimplifying Annan's answer, he says: AGW is a statistical theory about multidecadal warming - wait a few decades and see. Eli R points out some ancillary effects that are suitable tests.

I don't think Roger is being unreasonable in thinking that these answers are not quite to the point. Maybe we will have definitive answers in a few decades, but what about now? Are there no measurements that can test the theory?

It seems to me that there are some potential tests that examine the gears and wheels of the theory without the need to challenge the Boltzmann radiation law. The AGW theory is statistical because there are large unmodelled factors that affect global temperature.

Atmospheric CO2 has been increasing more or less steadily for many decades now, and with it the associated radiative forcing. The average global temperature has behaved in a much more complex fashion, presumably due to other forcings and to internal dynamics which are assumed to produce heating or cooling. Some of these dynamics likely just store heat in the deeper ocean, and are intrinsically confirmatory of AGW theory. Others change the radiative properties of the planet. These latter, if large enough and of appropriate sign, signal a potential threat to the theory - they represent a possible negative feedback.

Confirmation or disconfirmation of AGW theory must thus concentrate on understanding these dynamics, and capturing them in realistic models.

The above is not exactly an original insight. I'm sure that all the major players understand it well, and that is one reason that considerable effort goes into trying to understand exactly those dynamics. For some reason, though, these rather obvious facts are rarely discussed. Perhaps there is a fear that the discussion of the points would be construed as an admission of doubt.