We've discussed how a recent paper by a prominent climate contrarian had set off an exaggerated response in some corners of the popular press that ultimately contributed to the resignation of the editor of the journal that published it. But the paper remained part of the scientific literature, which, as we commented at the time, "Should induce his critics to get more thorough criticisms formally published." Apparently one was already in the works, and it was released over the weekend by Geophysical Research Letters. The paper focuses on the simplified model used in an attempt to indicate that clouds could force the climate, and shows that the model may not even be able to reproduce the conservation of energy.

The paper is the work of Andy Dessler, who focuses on understanding how clouds influence the climate (that's our coverage of some of his past work). Dessler lays out the usual understanding of clouds in the first sentence: as the climate changes, the clouds change in response, and may enhance or limit the change in climate. In contrast, he cites two papers (by Richard Lindzen and the recent one by Roy Spencer) where they use the same model of the climate to suggest that this causality can be reversed, and changes in clouds drive the climate to new states.

A quick run-through of the model, however, shows that it is "potentially problematic," which appears to be a bit of an understatement. "Heating of their climate system by the ocean (ΔF ocean > 0) causes an increase of energy in the ocean (C(dT s /dt) > 0), apparently violating energy conservation," Dessler notes. In other words, the model suggests that, by transferring energy from the ocean to the atmosphere, it's possible to increase the energy of the ocean. "While it may be possible to define the terms so that Eq. 1 conserves energy, [these papers] do not provide enough information to show that they have actually done so," Dessler deadpans. "However, to comprehensively evaluate the arguments of LC11 and SB11, I simply note this potential problem and assume in the rest of the paper that Eq. 1 is correct."

Dessler then turns to the 10-year period analyzed by Spencer, and uses real-world data to see what the model's implications are. Even under favorable assumptions (i.e., all of the energy trapped by clouds is a forcing, not a feedback), their contribution to the short-term climate is only a few percent of the total surface temperature change. The majority of the differences are driven by heat exchange with the oceans, which is in turn driven by the El Niño cycle (ENSO). He then goes on to demonstrate that the climate models that most closely reflect the actual data from this time period are those that most accurately model the ENSO.

Spencer's paper only plotted six of the 14 models that he and Dessler both examined. Based on Spencer's selection criteria (the three most sensitive models and the three least sensitive), he happened to plot the ones that fit the data the worst. Most of the remaining ones were actually a much better fit.

In the end, Dessler concludes that the model used by Spencer, for its flaws, actually recapitulates the mainstream understanding of climate science: clouds are a minor influence on short-term variations, which are driven primarily by the ENSO. And, accordingly, those climate models that do the best job of reproducing the ENSO provide the best fit to real-world data. None of this indicates that clouds are providing an important forcing that's driving the current period of climate change. "Suggestions that significant revisions to mainstream climate science are required are therefore not supported," Dessler concludes.

This does not, as some of climate science's critics are already implying, mean that Dessler is denying that clouds have an effect on the amount of sunlight reflected back into space. In fact, he recognizes that clouds could be a major influence on long-term climate trends; it's just that there's no evidence that they drive the climate over shorter time scales. And, for the longer time scales, there's no convincing mechanism that can explain how trends in cloud levels could occur without being driven by changes in the climate. Which is why they're considered a feedback rather than a climate forcing.

Geophysical Research Letters, 2011. DOI: 10.1029/2011GL049236 (About DOIs).