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