Sunday, January 8, 2012

Ray Pierrehumbert's peer review of Rancourt's planetary warming physics article "CO2 has little effect"

Dr. Denis Rancourt's "Most downloaded free-access scientific article about planetary warming physics" has been extensively commented upon and critiqued by Prof. Dr. Raymond Pierrehumbert (Louis Block Professor, Department of the Geophysical Sciences, The University of Chicago), arguably the leading establishment expert on such physics models.

See the complete email exchange HERE.

The complete email exchange was initiated by an email from Rancourt to the scientists at Real Climate and is posted HERE. Further replies will be posted as comments to the present blogpost (below).

Rancourt's January 8, 2012 email concludes:

"You are a recognized establishment-science expert in these simple models. You have not identified any errors in my model. I think you will agree that when a simple model contains no physics errors and no calculation errors and obtains correct results without over stretching (without seeking results that the model is not structurally able to legitimately obtain), then if you wish to argue that the model needs more complexity the onus is on you to demonstrate that the added complexity is required rather than being superfluous."

1 comment:

Philippe said...

Hi Denis,

I realized this has been published some months ago, however I just recently had the time to read it attentively.

In your abstract, you present the main results of your model:

"The double-layer atmosphere model with no free parameters provides: (a) a mean Earth surface temperature of +17oC, (b) a post-industrial warming due only to CO2 increase of δT = 0.4oC, (c) a temperature increase from doubling the present CO2 concentration alone (to 780 ppmv CO2; without water vapour feedback) equal to δT = 1.4oC, and (d) surface temperature response sensitivities that are approximately two orders of magnitude greater for solar irradiance and for planetary shortwave albedo and longwave emissivity than for the atmospheric greenhouse effect from CO2."

I note that result (a), the mean surface temperature, is calculated by Eq.13 based on only a few parameters (A, C, D, a_at) based on global energy fluxes from reference [1], as well as the mean surface emissivity . That is, result (a) is completely independent on your model to relate a_at to CO2 concentration. So even if the two-layer model gives a robust estimate of mean surface temperature (that is, factoring all the error bars of the parameters), it doesn't say anything about your treatment of CO2.

Regarding results (b) and (c) - the increase in T due to post-industrial CO2 increase and a potential doubling of CO2 - can one empirically measure the increase in T due to CO2 alone (that is, independently from all the other factors affecting T)? And if not, to which measurable quantity can we compare the model's results?

Finally, assuming result (d) - the two orders of magnitude difference in sensitivities for a 6.7% increase of each parameter - is correct, it's not clear to me how this result relates to the actual conditions: for one thing, CO2 has been increasing by over 30% from pre-industrial levels. Perhaps more importantly, the 6.7% solar irradiation variation is a seasonal cycle, not a monotonous increase as the case of CO2. (Also, your model explicitly deals with 'average Earth properties', which implies that seasonal cycles have already been averaged out).