Dispelling a Climate Change Skeptic's "Deception"

(Updated: Friday 5 Oct 19:15 PST)

A few weeks ago I heard a presentation from someone (hereafter person "A", to remain anonymous) who claimed that increasing CO2 concentrations won't cause significant global warming.  The highly technical argument sounded extremely implausible to me, but it has taken me a while to sort out the details.  This is worth commenting on because the argument is due to be presented in a high profile book due out next year from a very well known publisher.

I don't fault person A for falling for the "deception", but he could have been more critical given the sources he used to build up his argument.

The anti-warming argument was based on a figure from a non-peer reviewed "paper" available on the web.  The figure, in turn, was generated by a fellow named David Archibald using the "modtran" model server hosted by The University of Chicago.  The modtran model server is run by Professor David Archer , in the Department of Geophysical Sciences, to help his students with coursework.  I wrote to Professor Archer to clarify both the intended use of the model and the interpretation of the data.

The model is evidently reasonably well accepted in its description of infrared radiation adsorption by the atmosphere as a function of CO2 concentration, otherwise known as radiative forcing.  But it turns out that to estimate the resulting warming, you have to multiply the radiative forcing by the 'climate sensitivity parameter', which tells you how the atmosphere and oceans respond to added heat.  The climate sensitivity parameter is actually a distribution of values, and models of climate change are usually evaluated using several different values of the parameter.  David Archibald conveniently chose a value that is 40 times smaller than the most likely value in the distribution used by the IPCC.  The value is in the distribution describing the climate sensitivity parameter, to be sure, but it is way the hell out to the left, and very improbable.  Thus one can very accurately claim that Archibald used the correct radiative forcing numbers but he intentionally chose an estimate of climate sensitivity that nobody else believes is physically likely.

Professor Acher posted to RealClimate.org with the title, "My model, used for deception".  He is relatively circumspect, though still damning, in his criticism of Archibald.  The comments that follow his post, however, are ruthless.  It seems I set loose the hounds.

I take the time to write this because I have become more aware of late that many climate change skeptics seem to think that anthropogenic climate change (in particular, warming caused by CO2 emissions) is simply a political ploy with no basis in physical reality.  That kind of thinking denies not just climate change, but virtually all of the science our technological economy is built on.  (I will certainly admit some of the rhetoric surrounding climate change bothers me, and I am not comfortable with the idea of brainwashing children to harass their parents about buying hybrid cars.  See the 29 September WSJ, "Inconvenient Youths", or even the recent The Daily Show segment on absurdly over the top children's books from wingnuts on both the left and the right.)

I could care less at this point about the political side of the argument, and why people do or don't like Al Gore.  Physics is physics.  Science always wins.  Science is self-correcting, and over the long term there ain't no politics about it.  The U.S. was founded based on the enlightenment notions of tolerance and rational decision making.  Alas, those words aren't in the Constitution anywhere, and they are seldom uttered inside the Beltway these days.  But if we don't base our policy decisions on science, then we can just forget the U.S. as a viable economic entity, and thus as an entity capable of being the standard bearer of ideals that make this country worth living in and defending.