Posted on 8 April 2012 by dana1981

This is a re-post from Carbon Brief of a critique of the presentation discussed in Lindzen's London Illusions covering some of the same points as in our posts, and some others as well.

A team of UK climate experts has published a critique of a talk given by climate skeptic scientist Richard Lindzen a few weeks ago. The event was organised by the Campaign To Repeal the Climate Change Act.

Lindzen, a Professor of Meteorology at the Massachusetts Institute of Technology, was speaking at the House of Commons in a meeting chaired by Christopher Monckton. While the authors of the critique could agree with Lindzen on some grounds, they also found some pretty glaring inaccuracies in his talk.

Lindzen has published a large body of peer-reviewed work on climate change, but his work remains disputed. It's very popular with the skeptic end of the media and he is also member of the academic advisory council to Lord Lawson's Global Warming Policy Foundation.

His speech was criticised by the blog Skeptical Science. Climatologist Dr Gavin Schmidt also pointed out flaws in his presentation of temperature data at the blog Real Climate, resulting in an apology from Lindzen.

Now, several UK experts have got in on the act, offering their own critique of Lindzen's speech. They are climate physicists Professor Sir Brian Hoskins at Imperial College; Professor John Mitchell, of the University of Reading and the UK Met Office; Professor Keith Shine, University of Reading; Professor  Tim Palmer, University of Oxford; and Professor  Eric Wolff, British Antarctic Survey Science Leader.

Points of agreement

The critique starts with the key points on which Lindzen and the UK experts agree. They welcome Lindzen's acceptance of some well established 'knowns' of climate science, including:

"There has been a large increase of atmospheric concentrations of carbon dioxide and other greenhouse gases due to emissions resulting from human activity over the past 150 years [...] Global average surface temperature has very probably warmed by about 0.7°C in the same period [...] Increasing carbon dioxide alone, and in the absence of climate feedbacks, should cause about 1°C warming for each doubling."

"'Uncertain' doesn't imply 'unknown'"

The scientists also agree with Lindzen that scientists should base their arguments on "physical reasoning and data", and that uncertainties should not be exaggerated or ignored -  indeed these points are the ground rules by which scientists operate.

Where they disagree is on Lindzen's inference that scientific uncertainty means scientists are ignorant about some key issues, implying we then don't have to be concerned.

One of Lindzen's favourite arguments seems to be his criticism of our knowledge of cloud feedback processes. Climate models suggest a weak to moderate positive cloud feedback, but there are uncertainties associated with how this will change in the future.

In his speech Lindzen suggests that these uncertainties mean "we don't know if there is a problem". The team of experts disagree, saying:

"[Lindzen] is right to draw attention to uncertainties in climate change feedbacks e.g. associated with clouds. However, it is wrong to infer from this that we know nothing about these feedbacks. Contemporary science suggests unambiguously that there is a substantial risk that these feedbacks will lead to human induced surface temperature change considerably larger than 1 °C in global average this century and beyond."

According to the paper, Lindzen makes similar errors in his discussion on sea level rise, reconstructions of solar activity, and climate sensitivity - how much the world's average temperature would rise from a doubling of carbon dioxide in the atmosphere.

Inconsistencies in Lindzen's arguments

The team also point out some pretty glaring inconsistencies in Lindzen's take on some climate topics, for example:

"There is an interesting dichotomy in [Lindzen]'s line of argument between the implication in the rest of the presentation that the climate is rather insensitive to change, and the observation  that, on glacial interglacial scales, even very small changes in energy input led to massive change."

They say Lindzen is "not consistent in his discussion of the accuracy of past temperature data" or of climate models.

And elsewhere, the team say, Lindzen makes claims that are simply wrong:

"[Lindzen] claims that the derived sensitivity of climate to a doubling of CO2 is less than 1°C, based on the assumption that all the observed warming is due to atmospheric greenhouse gases. This claim would be wrong even without this assumption [...] The assumption itself is unjustifiable as it neglects other mechanisms that drive climate change."

Lindzen "does a disservice to the scientific method"

The team sums up Lindzen's presentation, saying:

"A pervasive aspect of [Lindzen]'s presentation was the conflation of uncertainty with ignorance; in his view, because we are uncertain about some aspect, we therefore know nothing about it and any estimate of it is mere guesswork. In this way we believe [he] does a disservice to the scientific method, which seeks to develop understanding in the face of inevitable uncertainties in our knowledge of the world in which we live. The scientific method has served society well for many hundreds of years, and we see no reason to doubt its validity for trying to quantify the risk of climate change and its impacts on society this century."

They go on to point out that Lindzen's arguments are not anywhere near sufficient to discount man-made climate change:

"[...] We reassert that there is a substantial risk of human-induced climate change considerably larger than 1°C in global average this century and beyond. There is nothing in [Lindzen']s talk to cast doubt on the existence of this risk."

Scientists in the service of politics?

At Real Climate, Schmidt points out the value of questioning established norms of climate science:

"[Lindzen] has, in times past, raised interesting critiques of the mainstream science. None of them, however, have stood the test of time - but exploring the issues was useful."

The two responses however argue that Lindzen's statements on climate science go beyond questioning the science, instead presenting scientific uncertainty as ignorance and meanwhile advocating against climate policymaking. It seems strange to us that Lindzen is so vocal about criticising climate scientists for being politicised while speaking at an event organised by a political campaign against the UK's Climate Change Act.

The scientists respond to this element of Lindzen's presentation, concluding:

"It is up to policymakers, not scientists, to decide whether governments should take concerted mitigating action to try to reduce [the risk of  human-induced warming above 1 degree celsius].  On this we do not comment."

Tim Palmer, one of the scientists who wrote this latest response, told us he felt it was important to respond in this case because Lindzen is "an established atmospheric scientist and hence likely to have some influence". He and the other scientists thought it was important to make it clear to UK policymakers that Lindzen's view that the threat of substantial climate change is minimal runs "completely counter to the view of almost all who work actively in the field."