Troy_CA has another excellent contribution to the continuing analysis of Dessler 2010 and Dessler 2011 (h/t Mosher for alerting me)

CA readers are aware that the sign of the regression coefficient from Dessler 2010 is reversed when CERES clear sky is used in combination with CERES all sky, instead of replacing CERES clear sky with ERA clear sky. Dessler purported to justify the substitution on the basis of a suggested bias in the CERES clear-sky, referring to Sohn and Bennartz 2008.

In my opinion, this passim reference hardly justifies a failure to disclose the adverse results using CERES clear sky. The adverse results should have been disclosed and discussed (just as Spencer and Braswell 2011 should have shown all relevant models in their justly criticized figure.)

Nick Stokes, rather predictably, swooned over Dessler’s supposed wisdom in replacing CERES clear sky with ERA clear sky. Some quotes:

What the reanalysis can then do is make the moisture correction so the humidity is representative of the whole atmosphere, not just the clear bits. I don’t know for sure that they do this, but I would expect so, since Dessler says that are using water vapor distributions. Then the reanalysis has a great advantage.

Instead of simply accepting this sort of arm-waving as proof, Troy_CA has carried out an insightful analysis, with some important conclusions that totally refute Nick’s swoon and, in the process, directly question the replacement of CERES clear sky with ERA clear sky and thus the conclusions of the original article:

the “dry-sky bias correction”, if it exists in ERA, accounts for very little of the difference we see between ERA_CRF and CERES_CRF

The bulk of these CERES_CRF vs. ERA_CRF differences come from this different value for the effective surface albedo. Note that this has nothing to do with a “dry-sky” longwave water vapor bias.

to me there seems to be little ambiguity that the magnitude of the positive feedback in Dessler10 is more of an artifact of combining two flux calculations that aren’t on the same page, rather than some bias correction in ERA-interim.

Following practices of critical climate blogs (I prefer “critical” to “skeptical”), Troy has commendably archived source code.

PS. I’ve obtained some source code from Dessler on some of the calculations in Dessler 2011 and will be posting on that.

PPS. Note that criticizing the analysis of Dessler (2010) does not imply that the conclusions of Spencer and Braswell are “right” (or that they are “wrong”).



