Clouds and climate skeptics - new paper critiques 'flawed' sceptic study

  • 07 Sep 2011, 11:00
  • Christian Hunt

A new paper (pdf - abstract here) published in the journal Geophysical Research Letters has been creating waves in the climate blogosphere today. The author of the paper is Andrew Dessler, a climate scientist at Texas A&M University, and the paper deals with the influence of clouds on the world's energy budget.

Dessler's paper has made notably speedy progress through the peer review and publication process. It is a response to a paper published by  Lindzen and Choi in May and another published just two months ago by  Spencer & Braswell in July in the journal 'Remote Sensing'.

The GRL paper also follows the unexpected resignation of the Editor-in-Chief of Remote Sensing just last week over his concerns about the publication of the Spencer and Braswell paper. As is often the case, the scientific debate is being a bit obscured by the internet noise, so what's actually going on?

The core of the argument is disagreement over whether global warming causes changes in cloud cover, or whether it's the other way around, and changes in clouds are causing warming. The latter is the favoured view of some climate skeptics, and runs counter to the weight of scientific understanding.

As the website Skeptical Science explains:

"The Spencer/Braswell and Lindzen/Choi papers have an unusual take on global warming: rather than warming causing a change in cloud cover (i.e. acting as a feedback to either increase or reduce warming), both papers claim that it's the other way around - changes in cloud cover cause changes in the surface temperature (in the present case, warming)."

When it was published in July the Spencer and Braswell paper prompted some fairly spectacular claims in the media - with headlines like New NASA Data Blow Gaping Hole In Global Warming Alarmism (Forbes) and Climate change far less serious than 'alarmists' predict says NASA scientist (the Daily Mail).

The paper was also heavily criticised by climate scientists and bloggers - with Kevin Trenberth and John Fasullo notably writing at RealClimate that despite the "impressive" "hype" around it, the paper had "no merit whatsoever".

Last Friday the editor of the journal which had published the Spencer/Braswell paper resigned over the matter, and issued a blistering resignation editorial [pdf], writing

"With this step I would also like to personally protest against how the authors and like-minded climate sceptics have much exaggerated the paper's conclusions in public statements"

He continued:

"I perceive this paper to be fundamentally flawed and therefore wrongly accepted by the journal."

He explained that

"... comparable studies published by other authors have already been refuted in open discussions and to some extent also in the literature (cf. [7]), a fact which was ignored by Spencer and Braswell in their paper and, unfortunately, not picked up by the reviewers. In other words, the problem I see with the paper by Spencer and Braswell is not that it declared a minority view (which was later unfortunately much exaggerated by the public media) but that it essentially ignored the scientific arguments of its opponents."

Dr Roy Spencer (who blogs here) is one of a small group of scientists who questions whether climate-change is man-made - and hence is something of a celebrity to climate skeptic bloggers and media outlets. After Wagner's resignation, he defended his paper on his website and on the website of the Global Warming Policy Foundation.

In an article on the US blog the Daily Climate last Friday, climate scientists  
Kevin Trenberth, John Abraham, and Peter Gleick attacked his previous publication record, stating

"Spencer, a University of Alabama, Huntsville, climatologist, and his colleagues have a history of making serious technical errors in their effort to cast doubt on the seriousness of climate change. Their errors date to the mid-1990s, when their satellite temperature record reportedly showed the lower atmosphere was cooling. As obvious and serious errors in that analysis were made public, Spencer and Christy were forced to revise their work several times and, not surprisingly, their findings agree better with those of other scientists around the world: the atmosphere is warming."

So has his latest paper been refuted? The new paper by Dessler published today starts by stating

"The usual way to think about clouds in the climate system is that they are a feedback - as the climate warms, clouds change in response and either amplify (positive cloud feedback) or ameliorate (negative cloud feedback) the initial change [e.g., Stephens, 2005].    In recent papers, Lindzen and Choi [2011, hereafter LC11] and Spencer and Braswell [2011, hereafter SB11] have argued that reality is reversed: clouds are the cause of, and not a feedback on, changes in surface temperature. If this claim is correct, then significant revisions to climate science may be required."

The paper then uses data from 2000 to 2010 and an energy budget calculation to show that:

"... the energy trapped by clouds accounts for little of the observed climate variations. And observations of the lagged response of top-of-atmosphere (TOA) energy fluxes to surface temperature variations are not evidence that clouds are causing climate change."

Dessler concludes:

"These calculations show that clouds did not cause significant climate change over the last decade (over the decades or centuries relevant for long-term climate change, on the other hand, clouds can indeed cause significant warming)...In addition, observations presented by LC11 [Linzen and Choi] and SB11 [Spencer and Braswell] are not in fundamental disagreement with mainstream climate models, nor do they provide evidence that clouds are causing climate change. Suggestions that significant revisions to mainstream climate science are required are therefore not supported."

For those who are interested, Skeptical Science has more on the Dessler paper here. Dessler himself has also produced a clear three minute video explaining his conclusions, which is worth a watch.

In his final slide he identifies that his paper has found:

-       No merit in the suggestion that clouds cause climate change

-       No merit in the claims that climate models as a group are 'wrong'

-       No evidence that revisions to mainstream climate science are required

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