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« Russell review due July 7 | Main | Andy Russell on the Hockey Stick »

On consensus

Some days ago I posted a short quote from a forthcoming paper by Mike Hulme. This is it:

Claims such as ‘2,500 of the world’s leading scientists have reached a consensus that human activities are having a significant influence on the climate’ are disingenuous. That particular consensus judgement, as are many others in the IPCC reports, is reached by only a few dozen experts in the specific field of detection and attribution studies; other IPCC authors are experts in other fields.

As is my wont, I set out Hulme's own words unadorned, leaving readers to draw their own conclusions. There were certainly a great many conclusions drawn, with Marc Morano Larry Solomon and others repeating the quote and filling in the blanks. Solomon, for example, said:

The UN’s Intergovernmental Panel on Climate Change misled the press and public into believing that thousands of scientists backed its claims on manmade global warming, according to Mike Hulme, a prominent climate scientist and IPCC insider.

Hulme now appears to have taken umbrage and has issued a statement clarifying his views. 

I did not say the ‘IPCC misleads’ anyone – it is claims that are made by other commentators, such as the caricatured claim I offer in the paper, that have the potential to mislead.

This is certainly true - Hulme did not discuss the IPCC in this context, but the question must remain of whether the IPCC was the source of the "2500 scientists" claim, the one that Hulme describes as "misleading". If the IPCC was behind it then the claims of Morano et al. are quite correct.

Hulme goes on to discuss the meaning of the word "consensus" in the context of IPCC reports.

The point of this bit of our article was to draw attention to the need for a more nuanced understanding of what an IPCC ‘consensus’ is – as I say: “Without a careful explanation about what it means, this drive for consensus can leave the IPCC vulnerable to outside criticism.” The IPCC consensus does not mean – clearly cannot possibly mean – that every scientist involved in the IPCC process agrees with every single statement in the IPCC!

In normal discourse, the word "consensus" means "agreement of various parts, agreements in opinion, unanimity" (Chambers Dictionary). In other words, the use of the word "consensus" would imply to most people that scientists were all in agreement, an idea that Hulme quite correctly sees as risible. (One should note in passing however that it is probably symptomatic of climate denial to say so).

There is also a secondary meaning, one which my dictionary says can only be used "loosely", and this meaning is "trend of opinion". It could be that this is the sense of the word that the IPCC has adopted. However, it's not even clear that what Hulme is describing is a "trend of opinion", except perhaps among the small select group responsible for the detection and attribution chapter of the IPCC report. So when we stand back a little, the word consensus has shifted from unanimity among 2500 scientists to the trend of opinion among them and has ended up as the trend of opinion of a mere couple of dozen.

There is surely no doubt that the decision to talk of "consensus" was a political one, designed to influence the public and policymakers and to keep the money flowing into climatology. If this spinning and deception now comes back to bite the backsides of some of the prime movers in the global warming movement, so much the better.

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Reader Comments (32)

It has always seemed clear to me that "consensus" is more a political term than one that should be applied to science. A scientific hypothesis lives and dies on whether evidence supports the hypothesis, not whether (some, perhaps 50%+) scientists agree with the hypothesis.

Jun 16, 2010 at 10:19 AM | Unregistered CommenterPhillip Bratby

There is some serious backpedalling going on, trying to re-write history and justify the unjustifiable.

The time for people like Hulme to be stating "Claims such as ‘2,500 of the world’s leading scientists have reached a consensus that human activities are having a significant influence on the climate’ are disingenuous" was a few years back, when politicians and the media were unthinkingly parroting such statements.

It's a bit late, now that the claim has been widely exposed as rubbish, to start nit-picking about the precise meaning of the word "concensus" and pretending that it never meant what everyone thought it meant.

Jun 16, 2010 at 10:30 AM | Unregistered CommenterMartin A

The Shorter Oxford English Dictionary (2007) is often considered to be the most authoritative two-volume dictionary (I prefer it to the OED). Its definition is as follows.

consensus noun.
Agreement or unity of or of opinion, testimony, etc.; the majority view, a collective opinion; (an agreement by different parties to) a shared body of views.

Jun 16, 2010 at 10:33 AM | Unregistered CommenterDouglas J. Keenan

This is an extract from my post on the IAC and was prompted by the inclusion of Goverdhan Mehta, Past President of the International Council for Science (ICSU)

It shows the small world of the scientists who make up the "scientific consensus". This description is from the ICSU website.

"Currently, there are four global environmental change programmes co-sponsored by ICSU—the World Climate Research Programme (WCRP), International Geosphere-Biosphere Programme (IGBP), International Human Dimensions Programme (IHDP) and DIVERSITAS (an international programme on biodiversity). Together, these programmes promote, coordinate and integrate over 2 billion euros of research and provide the scientific basis for major international assessments and conventions, including the work of the Intergovernmental Panel on Climate Change."

In a powerpoint slide from an Earth System Science Partnership, (ESSP), presentation, in 2008, Susan Solomon says almost half of the contributors to IPCC AR4 are WCRP/IGBP/IHDP/Diversitas associated scientists.

Here are Solomon’s very revealing figures:

· 91% of Co-ordinating Lead Authors on AR4 were members of this grouping
· 66% of Lead Authors on AR4 were members of this grouping
· 68% of reviewers on AR4 were from this grouping
· 31% of contributing authors were from this grouping

World Climate Research Program, (WRCP) an offshoot of the WMO.
Kevin Trenberth is Chairman of WRCP Observations and Assimilation Panel. Trenberth is currently head of Climate Analysis at NCAR.

International Geosphere – Biosphere Program (IGBP)
ICSU appointees to IGBP include Ray Bradley, Jean Palutikof, a former Director of CRU and now spreading the message in Australia.

International Human Dimensions Program on Global Climate Change, (IHDP), is more global governance by the UN,

Diversitas is another group-think eco-catastrophe outfit with Paul Ehrlich on its advisory board. Its founding sponsors are the United Nations Educational, Scientific and Cultural Organization (UNESCO), the Scientific Committee on Problems of the Environment (SCOPE) and the International Union of Biological Science (IUBS)

As Founding Director of the Tyndall Centre, Hulme was responsible for much of the climate hysteria from which he now tries to dissociate himself, being responsible in part, amongst other scary initiatives, for the UK Climate Impacts Programme, 2002.

For an excellent treatment and discussion of Hulme's post-normal science check out

Jun 16, 2010 at 10:50 AM | Unregistered CommenterDennisA

I quite clearly remember the BBC news items at the time of the conference and direct from the conference. Consistently "2,500 scientists" with "90%" etc. I remember it so well because of course I thought what a load of...

If the BBC were doing reporting/propaganda directly from the location then you can guarantee this came from the IPCC spin doctors... or the consensus between the group think of the journalists.

The IPCC had the opportunity to clearly set the record straight at that time. which they did not do. Which is de facto an endorsement based on the proximity of the parties and short communication lines during those weeks.

Jun 16, 2010 at 11:17 AM | Unregistered CommenterJiminy Cricket

Now I'm really confused ! Is there a consensus now or what? I think the consensus must have changed to ..'quick nuance the history' before the brown stuff hits the spinning thingy.

I can hear the 'beep beep' sound of a juggernaut reversing from here.....

Jun 16, 2010 at 11:33 AM | Unregistered Commenterconfused

When everyone is fibbing --or speaking jibberish-- it is very difficult to determine the truth in the statements they are making. In fact, it is a waste of time and energy to even attempt to do so. Why is everyone fibbing --or speaking jibberish-- on the subject at hand? They're in the dark. They have no idea what the truth is. They're "swagging" it.

Jun 16, 2010 at 12:51 PM | Unregistered CommenterPascvaks

In the particular context of science, 'consensus' usually means that fundamental debate has ceased (although it may continue on the details) and a prevailing view is shared by most scientists concerned.
The '2500 scientists' idea comes probably from the number of authors cited in the IPCC report, which is of course totally unrelated to any 'consensus' on particular points, especially because many of the 2500 present conflicting results on their particular fields. On any specific point, say temperatures in the latest 1000 years or the future behavior of El Niño, it is a much smaller number of scientists who may be in consensus or disensus. The rest would probably stick to their field of specialization and say nothing on other matters. The fact that, say, an agricultural scientist declares that she agrees with the view that Greenland is rapidly melting is not of much significance, since she is only expressing her agreement on conclusions she is not involved with and on which she has no expertise.

On the other hand, deliberate selection of favorable views (and exclusion of dissenters) would probably create the impression of a higher consensus that actually exists.

Jun 16, 2010 at 1:55 PM | Unregistered CommenterHector M.

The last phrase of my previous comment should read "than actually exists". Sorry.

Jun 16, 2010 at 1:58 PM | Unregistered CommenterHector M.

"The last phrase of my previous comment should read "than actually exists". Sorry."

I had to look several times to find the difference.

The brain skates over many typos so it's hardly worth correcting errors that probably won't even be noticed - unless the typo changes the sense of what's being said.

Jun 16, 2010 at 2:05 PM | Unregistered CommenterMartin A

And STILL they won't give up - I saw the following article in a local paper and my blood pressure went through the roof:

Now it's not sufficient to have a "Low Carbon Economy", they want a "ZERO Carbon Economy"

Jun 16, 2010 at 2:25 PM | Unregistered Commenterdave ward

Well, there seems to be less "consensus" in the US Congress even with the oil spill.


Jun 16, 2010 at 2:35 PM | Unregistered CommenterDon Pablo de la Sierra

Perhaps the Congress needs to tell Patchi…. Not only is there back peddling but it seems they are spreading the load too…..

Dr R K Pachauri

I would like to start by saying that I am not deaf to those who do not agree with the scientific consensus on man-made climate change.
Nor, indeed, to those who do not agree with the findings - or, in some cases, the existence - of the IPCC.
Such scepticism is inevitable, and has been the case with every area of new knowledge that has burst into human consciousness.
We who are on the side of the consensus must remind ourselves that the evolution of knowledge thrives on debate.

Shared responsibility
The Intergovernmental Panel on Climate Change (IPCC) was established in 1988 through the mandate of the UN General Assembly.

It is not - and it is important to remember this - a UN body but, as its title suggests, an intergovernmental organisation, which means that ultimately its decisions have to be taken by the panel as a whole (ie all the governments of the world).

Jun 16, 2010 at 2:44 PM | Unregistered Commentermartyn

I always urge people to study VERY closely what it is that is being claimed as the subject of the consensus. It is usually so trivial, or so surrounded by 'coulds' and 'mays' and 'mights' as to be essentially meaningless.

For example the following was released in Texas a month or two back by some academics/universities, as being indicative of the 'consensus'

• • The global climate is changing.
• • Human activities produce heat-trapping gases.
• • Heat-trapping gases are very likely responsible for most of the warming observed over the past half century. No one has been able to propose a credible alternative.
• • The higher the levels of heat-trapping gases in the atmosphere, the higher the risk of potentially dangerous consequences for humans and our environment.

The first two are a fatuous stating of the obvious. The final two, meaningless vague assertions.

This then, is the much vaunted 'consensus' on which the mighty edifice of climate science rests.


Jun 16, 2010 at 2:57 PM | Unregistered CommenterChuckles

I listened to Martin Rees 1st reith lecture and here again it is all "wernot certain but co2 is a blanket you know so there is an effect..we shod insure ourselves.."

I think the consensus is there is a blanket effect.

However having an extra blanket for the road is beneficial. Not something I want to take an "insurance"against..

Jun 16, 2010 at 5:13 PM | Unregistered CommenterPhinnietw


While I realize what your position is, perhaps a few responses to the talking points:

• • The global climate is changing.

Duh! So what's new? Been doing it for millions of years.

• • Human activities produce heat-trapping gases.

But so do animals, namely cows who fart methane into the air. And then there is that volcano in Iceland with a name nobody can pronounce. Not to mention other volcanoes all over the world. Then we could move on to the nasty Sun which produces billions of pounds of water vapor every day by evaporation of the oceans and seas.

• • Heat-trapping gases are very likely responsible for most of the warming observed over the past half century. No one has been able to propose a credible alternative.

How about the simple fact that the global temperature has varied noticeably over the last 1500 years -- oops! I forgot that that was erased. However the Romans did grow grapes in northern England and make wine while they were running the place, and according to Leif Ericson, they had nice pastures in Greenland.

• • The higher the levels of heat-trapping gases in the atmosphere, the higher the risk of potentially dangerous consequences for humans and our environment.

If true, we should turn off the Sun and stop it from pumping water vapor into the air. Yes, indeed, we need to stop the Sun from destroying us all.

Jun 16, 2010 at 5:28 PM | Unregistered CommenterDon Pablo de la Sierra

I wish someone could explain to me this property of gases to trap heat. I thought a molecule of say CO2, when it absorbs a bit of IR, either rapidly re-radiates it or gives it to another molecule by collision. Convection and radiation soon get rid of the excess heat compared to the neighbouring molecules. The only blanket we have in the atmosphere is clouds, which are water droplets, not gas. Water vapour holds a ot of energy, but latent heat is something entirely different.

Jun 16, 2010 at 5:33 PM | Unregistered CommenterPhillip Bratby

I actually posted this once before in relation to Consensus. It is almost 5 pages of a very interesting and thoughtful interpretation on what concensus is, and how it can be achieved by controlling the masses and how they think. Well worth a read.


Jun 16, 2010 at 5:35 PM | Unregistered CommenterRETEPHSLAW

Philip Bratby,

The physics of the greenhouse effect is a lot more complicated than the usual media version would give you the impression.

There's a short and reasonably understandable version here.

Jun 16, 2010 at 7:24 PM | Unregistered CommenterArima

Phillip Bratby

I wish someone could explain to me this property of gases to trap heat.

While I can't explain Stefan-Boltmann’s Radiation Law, I know someone who can -- Claes Johnson. Full of equations and physics, and just the thing to put you asleep unless you know something about physics, math and all that. However, it is quite good if you do, as I believe you do.


Jun 16, 2010 at 8:16 PM | Unregistered CommenterDon Pablo de la Sierra

Arima and Don Pablo:

"I wish someone could explain to me this property of gases to trap heat."

I was being tongue-in-cheek when I wrote that.

Jun 16, 2010 at 9:10 PM | Unregistered CommenterPhillip Bratby

Phillip Bratby

"My name is Phillip Bratby. I have a first class honours degree in physics from the Imperial College of Science and Technology (London University) and a doctorate in physics from Sheffield University. "

We know. But there are others who would like to know. It was posted for them :)

Jun 17, 2010 at 1:39 AM | Unregistered CommenterDon Pablo de la Sierra

Even if they themselves did not promote this incorrect position, wouldn't they be obligated to clarify that it isn't correct? Something they obviously did not do.

Jun 17, 2010 at 2:31 AM | Unregistered Commenterkuhnkat

I think Mike Hulme is being a tad disingenuous when he discusses "consensus" and its origins. It's right here in the climategate emails and he was party to its birth. Apparently he didnt' do as Alcamo asks him in this email. Or am I taking it all out of context?

Jun 17, 2010 at 6:21 AM | Unregistered Commentergeronimo

Arima and Don Pablo:

I forgot to thank you for the useful links. Thanks. I hope others find them useful.

Jun 17, 2010 at 6:29 AM | Unregistered CommenterPhillip Bratby

Hulme's disingenuous attempts to distance himself from the import of his own words are actually worse than we thought :-)

As Geronimo noted above, Hulme certainly did contribute to the contrivance of the original pre-Kyoto "consensus", (see The fog of uncertainty and the precautionary principle) But I digress ...

The "2500" refers to the number of "Expert Reviewers". There were approximately 34,000+ Reviewer Comments on the Second Order Draft. Of these, 8905 (from a total of 307 Reviewers) were for WG1.

Of the 8905, only 3810 could be categorized as unambiguously "Accepted" by the "Chapter Team". Even if one adds the 180 "Agreed", [for a total of 3990 from 263 of the 307 reviewers]this is far from a majority, let alone a "consensus". Except perhaps amongst the Chapter Team - no doubt the "few dozen" to whom Hulme referred! Which, come to think of it, is - in itself - a rather telling comment on the weight that is given to the opinions of the Reviewers, is it not?

Consider, as well, that there's no way of knowing how many of the 307 actually read the entire WG1 Report.

This "consensus" is melting faster than a disappearing Himalayan glacier! I guess that in the world of climate science, "consensus" can be redefined as readily as .... hmmmm ..."peer review"?!

No wonder Hulme depicts the "idea of climate change [as] so plastic".

Jun 17, 2010 at 11:12 AM | Unregistered Commenterhro001

It seems Hume is trying to distance himself personally from the obvious frauds going on & which he has long endorsed as "post normal science" while doing his best not to be seen as in any way weakenong the frauds' influence.

"Consensus" is a word with no arithmetically definable meaning. It is typical that it should be used by eco-charlatans & politicians.

Jun 17, 2010 at 1:45 PM | Unregistered CommenterNeil Craig

It would clearly seem to me, that the 'consensus' story would be over much in the public interest for the bbc to report on?

Mike Hulme:

"Claims such as ‘2,500 of the world’s leading scientists have reached a consensus
that human activities are having a significant influence on the climate’ are disingenuous.
That particular consensus judgement, as are many others in the IPCC reports, is reached
by only a few dozen experts in the specific field of detection and attribution studies;
other IPCC authors are experts in other fields.

Especially in light of a climategate email discussion pre-kyoyo about consensus:

Mike Hulme for over 13 years has NEVER spoken up and said this IPCC consensu mantra is disengenous before:

Yet Mike Hulme was party to a number of climategate emails, where they discussed how to get a pr 1000's of scientists consensusstatement message to the media pre Kyoto

With just months until the Kyoto Climate Conference, we find the germ of this idea fertilizing in an email from Joe Alcamo,

Director of the Center for Environmental Systems Research in Germany, to Mike Hulme and Rob Swart:

"I think the only thing that counts is numbers. The media is going to say "1000 scientists signed" or "1500 signed".
No one is going to check if it is 600 with PhDs versus 2000 without. They will mention the prominent ones, but that is a different story."

I wonder if the media/politicians appreciate how they were being spun even then?

Jun 17, 2010 at 2:24 PM | Unregistered CommenterBarry Woods

Mike Hulme previoulsy ORGANISED sending out another consensus statement out for the signturies to sign! - 1997 pre kyoto..

The whole 2500 scientists thing, seems to have started much later, 2007?
possibly based ont hings like this, or just those involved in ar4, or just a made up comment for an interview/press release endlessly repeated..

Mike Hulme:
"Reference: Statement of European Climate Scientists on Actions to Protect
Global Climate

Dear Colleague,

Attached at the end of this email is a Statement, the purpose of which is
to bolster or increase governmental and public support for controls of
emissions of greenhouse gases in European and other industrialised
countries in the negotiations during the Kyoto Climate Conference in
December 1997. The Statement was drafted by a number of prominent European
scientists concerned with the climate issue, 11 of whom are listed after
the Statement and who are acting as formal sponsors of the Statement.......

..........We realize that you are very busy, but this action may have a very positive
influence on public discussions during the critical period leading up to
Kyoto and during the Conference itself.

With best wishes,
Michael Hulme, Climatic Research Unit, UEA, Norwich
Joseph Alcamo, University of Kassel, Germany"

sent and collated by Tim Mitchell - PHD student CRU, at MIKE HULMES request?! (missing Tim the programmer - in Harry_read_me.txt

Tom Wrigley email response was devastingly critical:

"I was very disturbed by your recent letter, and your attempt to get
others to endorse it. Not only do I disagree with the content of
this letter, but I also believe that you have severely distorted the
IPCC "view" when you say that "the latest IPCC assessment makes a
convincing economic case for immediate control of emissions." .

"It is not IPCC's role to make "convincing cases"
for any particular policy option; nor does it. However, most IPCC readers
would draw the conclusion that the balance of economic evidence favors the
emissions trajectories given in the WRE paper. This is contrary to your

"This is a complex issue, and your misrepresentation of it does you a
dis-service. To someone like me, who knows the science, it is
apparent that you are presenting a personal view, not an informed,
balanced scientific assessment. What is unfortunate is that this will not
be apparent to the vast majority of scientists you have contacted.

In issues like this, scientists have an added responsibility to keep their
personal views separate from the science, and to make it clear to others
when they diverge from the objectivity they (hopefully) adhere to in their
scientific research. I think you have failed to do this.

People who endorse your letter will NOT have "carefully examined" the issue.

When scientists color the science with their own PERSONAL views or make
categorical statements without presenting the evidence for such
statements, they have a clear responsibility to state that that is what
they are doing. You have failed to do so. Indeed, what you are doing is,
in my view, a form of dishonesty more subtle but no less egregious than
the statements made by the greenhouse skeptics, Michaels, Singer et al. I
find this extremely disturbing.

Tom Wigley"

There is a lot more criticism, see the full email below
(statement from Tom Wrigley's response Mike Hulme, tim mitchell statement underneath )
search for:
Statement of European Climate Scientists on Actions to Protect

the climategate email, list all thos names it was sent out to... (13 years ago)
some of these names below:

Sir Professor John Houghton in there, Chair IPCC three reports
Professor Nigel Arnell - now director Walker Institute fro Climate Change Research
Professor Julia Slingo - Now chief scientis at the Met office.

Scientists trying to drive public policy even then..

Jun 17, 2010 at 2:31 PM | Unregistered CommenterBarry Woods

Barry I'm not sure Prof Hulme, in fact took part in this charade, the letter was sent from Mitchell, there's no mention of Hulme's involvement.

Jun 17, 2010 at 5:33 PM | Unregistered Commentergeronimo

tmitchell was a phd student at the time, he sent the email statement on Mike Hulme's behalf, organised collation..(ie the donkey work)

Mike Hulme was responsible, see signed statement below....

From the statement:

"We realize that you are very busy, but this action may have a very positive
influence on public discussions during the critical period leading up to
Kyoto and during the Conference itself.

With best wishes,

Michael Hulme, Climatic Research Unit, UEA, Norwich
Joseph Alcamo, University of Kassel, Germany

(On behalf of the other signatories of the Statement)"

Jun 17, 2010 at 6:08 PM | Unregistered Commenterbarry woods

Very last bit of the email, look for yourself, link attached, search for the text mentioned.

> ** This message originated from the
> ** Climatic Research Unit, University of East Anglia, Norwich, UK.
> ** It was sent out by
> ** Mike Hulme and Tim Mitchell on behalf of the 11 key signatories.
> ** If you object to being on this email address list,
> ** please accept our apologies and inform us;
> ** we will then remove your address from the list.
> ** Please direct any comments to:
> **
> ************************************************************************
> The list below consists of the people with UK email addresses to whom this
> message has been sent:
> all CRU staff
Tim Mitchell had just started his phd, Hulme was his boss.

search in the search box for:

Statement of European Climate Scientists on Actions to Protect

Jun 17, 2010 at 6:25 PM | Unregistered Commenterbarry woods

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