For and against the "97% Consensus"

Climate sceptics are fond of challenging the oft-vaunted claim that 97% of climate scientists agree that current global warming is largely caused by mankind – the word commonly used is “anthropogenic”. So can that 97% figure be justified? Do the sceptics have a point?

Why 97%?  

This figure was arrived at in a study made in 2013 that examined the abstracts of nearly 12,000 papers on climate published between 1991 and 2011 in peer-reviewed journals. The criterion for including an abstract was a match with the terms “global climate change” or “global warming”.

Of these 12,000 abstracts, many (66.4%) did not offer an opinion on anthropogenic global warming (AGW), but of those that did (around 4,000 papers), 97.1% endorsed the consensus view that human activity is responsible for global warming.

The study (lead author John Cook of the Global Change Institute, Queensland, Australia) was published in the highly reputable Environmental Research Letters (Vol 8, No 2).

The overall conclusion of the study was: Our analysis indicates that the number of papers rejecting the consensus on AGW is a vanishingly small proportion of the published research.

This is not the only study that has produced a figure very close to 97%. For example, in 2009 Doran and Zimmermann concluded a 97% consensus, and in 2010 Anderegg et al reckoned that the actual figure was 97.5%. These researchers would have used different methods and criteria than those of Cook et al.

Cook et al also looked at the public’s perception of the consensus, and found a marked “consensus gap”. A representative sample of American people was asked the question: “How many scientists agree that humans are causing global warming?” The average response was around 50%, which therefore reveals a huge public misconception about what climate scientists believe is the cause of global warming.

The opposing view

This was expressed in the oft-quoted “Petition Project” that is widely touted as offering proof that the “97% consensus” figure is wildly optimistic.

The petition in question dates from 2007 and was issued by the “Oregon Institute of Science and Medicine”. By 2013 the petition organisers claimed that more than 32,000 American scientists had signed the petition, the main statement of which was:

“There is no convincing scientific evidence that human release of carbon dioxide, methane, or other greenhouse gases is causing or will, in the foreseeable future, cause catastrophic heating of the Earth's atmosphere and disruption of the Earth's climate.”

The fact that so many qualified people were prepared to put their names to this statement is taken as evidence that the 97% consensus must be false and that there is a considerable body of informed opinion that takes a very different point of view.

To be fair, it must be pointed out that the “Oregon Petition” is not the only attempt to come up with a similar conclusion. However, the attention directed towards the Petition, and the reliance placed on it by climate change deniers, make it a fair target for close examination.

A bogus petition

There are several circumstances surrounding the Petition that lead to the conclusion that it should not be taken seriously.

One of these is the status of the “Oregon Institute of Science and Medicine”. It sounds impressive, but in actual fact it is nothing of the sort. It sounds as though it ought to be research facility or a college, staffed by highly-qualified and well-respected personnel who undertake research at a high level and publish quality papers in the world’s leading scientific journals.

It turns out that the “Oregon Institute” is nothing more than a cover name for a small group of climate change deniers led by Dr Arthur B Robinson, whose doctorate is in chemistry. He has done no research in climate science and his motivation for entering the field appears to be entirely political (he has stood for the US Congress as a Republican).

As for the Petition itself, it claimed to be based on a rigorous selection procedure that ensured that it was only signed by suitably qualified people. In reality, anyone with a Bachelor’s degree in a scientific discipline was entitled to sign it, and very few checks were carried out with a view to weeding out signatories who were doing so from a purely political motive.

The reality is that the criteria for signing were so weak that more than 10 million people were qualified to sign, and 32,000 therefore represents a tiny minority of potential signatories.

The Petition was accompanied by an initially impressive document that appeared to be a reprint from a peer-reviewed journal and to be endorsed by the National Academy of Science.  This paper included graphs and other “evidence” that poured scorn on the consensus view of global warming. However, it was riddled with errors and misleading statements – so much so that the National Academy felt constrained to issue a rejoinder that dissociated itself from the Petition and declared that it was “a deliberate attempt to mislead scientists”.

Who do you trust?

So the question boils down to – Who do you trust to be more reliable when it comes to speaking the truth about the consensus on global warming?

On the one hand you have rigorous studies, conducted by people with pristine credentials, that make use of sound research published in peer-reviewed journals. On the other hand you have politically-motivated “cod science” in the form of a petition organised by highly dubious individuals and conducted in a manner that was far from scientific and nowhere close to being statistically sound.

And yet, for reasons best known to themselves, the climate change deniers tell us that we should be paying more attention to the latter than the former!

© John Welford