At the outset, let's be quite clear: There is no consensus about dangerous anthropogenic global warming (DAGW) -- and there never was.  There is not even a consensus on whether human activities, such as burning fossil fuels to produce useful energy, affect global climate significantly.  So what's all this fuss about?

Let's also be quite clear that science does not work by way of consensus.  Science does not progress by appeal to authority; in fact, major scientific advances usually come from outside the consensus; one can cite many classic examples, from Galileo to Einstein.  [Another way to phrase this issue: Scientific veracity does not depend on fashionable thinking.]  In other words, the very notion of a scientific consensus is unscientific.

The degree of consensus also depends on the way the questions are phrased.  For example, we can get 100% consensus if the question is "Do you believe in climate change?"  We can get a near-100% consensus if the question is "Do you believe that humans have some effect on the climate?"  This latter question also would include also local effects, like urbanization, clearing of forests, agriculture, etc.

So one has to be rather careful and always ask: What is the exact question for which a consensus has been claimed?

Subverting Peer Review

Finally, we should point out that a consensus can be manufactured -- even where no consensus exists.  For example, it has become very popular to claim that 97% of all publications support AGW.  Here the key question to ask is: Which publications and what exactly is the form of support?

Thanks to the revelations of the Climategate e-mails, we now have a more skeptical view about the process which is used to vet publications.  We know now that peer-review, once considered by many as the 'gold-standard,' can be manipulated -- and in fact has been manipulated by a gang of UK and US climate scientists who have been very open about their aim to keep dissenting views from being published.  We also know from the same e-mails that editors can be bullied by determined activists.

In any case, the peer-review process can easily be slanted by the editor, who usually selects the reviewers.  And some editors misuse their position to advance their personal biases.

We have, for example, the case of a former editor of Science who was quite open about his belief in DAGW, and actively discouraged publication of any papers that went against his bias.  Finally, he had to be shamed into giving voice to a climate skeptic's contrary opinion, based on solid scientific evidence.  But of course, he reserved to himself the last word in the debate.

My occasional scientific coauthors David Douglass (U. of Rochester) and John Christy (U. of Alabama, Huntsville) describe a particularly egregious instance of the blatant subversion of peer-review -- all supported by evidence from Climategate e-mails.

Confusing the Issue

Further, we should mention the possibility of confusing the public, and often many scientists as well, by clever use of words.  I will give just two examples:

It is often pointed out that there has been essentially no warming trend in the last 15 years -- even though greenhouse forcing from carbon dioxide has been steadily increasing.  At the same time, climate activists claim that the past decade is the warmest since thermometer records were started.

It happens that both statements are true; yet they do not contradict each other.  How is this possible?

We are dealing here with a case of simple confusion.  On the one hand we have a temperature trend which has been essentially zero for at least 15 years.  On the other hand, we have a temperature level which is highest since the Little Ice Age ended, around 1800 A.D.

Note that 'level' and 'trend' are quite different concepts -- and even use different units.  Level is measured in degreesC; trend is measured in degC per decade.  [This is a very general problem; for example, many people confuse electric energy with electric power; one is measured in joules or kilowatt-hours; the other is measured in kilowatts.]

It may help here to think of prices on the stock market.  The Dow-Jones index has more or less been level for the last several weeks, fluctuating between 15,000 and 16,000, showing essentially a zero trend; but it is at its highest level since the D-J index was started in 1896.

This is only one example by which climate activists can confuse the public -- and often even themselves -- into believing that there is a consensus on DAGW.   Look at two typical recent headlines:

               "2013 sixth-hottest year, confirms long-term warming: UN"
               "U.S. Dec/Jan Temperatures 3rd Coldest in 30 Years"

Both are correct, but neither mentions the important fact that the trend has been flat for at least 15 years -- thus falsifying the greenhouse climate models, all of which predict a strong future warming.

And of course, government climate policies are all based on such unvalidated climate models -- which have already been proven wrong.  Yet the latest UN-IPCC report of Sept 2013 claims to be 95% certain about DAGW!  Aware of the actual temperature data, how can they claim this and keep a straight face?

Their laughable answer: 95% of climate models agree; therefore the observations must be wrong!  One can only shake one's head sadly at such a display of "science."

Another trick question by activists trying to sell a "consensus": "If you are seriously ill and 99 doctors recommend a certain treatment, would you go with the one doctor who disagrees?" 

It all depends.  Suppose I do some research and find that all 99 doctors got their information from a single (anonymous) article in Wikipedia, what then?

Opinion Polls

Both sides in the climate debate have made active use of opinion polls.  In 1990, when I started to become seriously involved in climate-change arguments and incorporated the SEPP (Science & Environmental Policy Project), I decided to poll the experts.  Having limited funds, and before the advent of widespread e-mail, I polled the officers of the listed technical committees of the American Meteorological Society -- a sample of less than 100.  I figured those must be the experts.

I took the precaution of isolating myself from this survey by enlisting the cooperation of Dr Jay Winston, a widely respected meteorologist, skeptical of climate skeptics.  And I employed two graduate students who had no discernible expertise in climate issues to conduct the actual survey and analyze the returns.

This exercise produced an interesting result: Roughly half of the AMS experts believed there must be a significant human influence on the climate through the release of carbon dioxide -- while the other half had considerable doubt about the validity of climate models.

Subsequent polls, for example those by Hans von Storch in Germany, have given similar results -- while polls conducted by activists have consistently shown strong support for AGW.  A classic case is a survey of the abstracts of nearly 1000 papers, by science historian Naomi Oreskes (UC San Diego); published in 2004 Science, she claimed a near-unanimous consensus about AGW.  However, after being challenged, Oreskes discovered having overlooked some 11,000 abstracts -- and published a discreet Correction in a later issue of Science.

On the other hand, independent polls by newspapers, by Pew, Gallup, and other respected organizations, using much larger samples, have mirrored the results of my earlier AMS poll.  But what has been most interesting is the gradual decline over the years in public support for DAGW, as shown by these independent polls.

Over the years also, there have been a large number of "declarations, manifestos, and petitions" -- signed by scientists, and designed to influence public opinion -- starting with the "Leipzig Declaration" of 1995.  Noteworthy among the many is the Copenhagen Diagnosis (2009), published to build up hype for a UN conference that failed utterly.

It is safe to say that the overall impact of such polls has been minimal, compared to the political consequences of UN-IPCC (Inter-governmental Panel on Climate Change) reports that led to (mostly failed) attempts at international action, like the Kyoto Protocol (1997-2012).  One should mention here the Oregon Petition against Kyoto, signed by some 31,000 (mostly US) scientists and engineers -- nearly 10,000 with advanced degrees.  More important perhaps, in July 1997 the US Senate passed the Byrd-Hagel Resolution against a Kyoto-like treaty by unanimous vote -- which probably dissuaded the Clinton-Gore White House from ever submitting Kyoto for Senate ratification.

Is Consensus still an issue?

By now, the question of a scientific consensus on AGW may have become largely academic.  What counts are the actual climate observations, which have shaken public faith in climate models that preach DAGW.  The wild claims of the IPCC are being offset by the more sober, fact-based publications of the NIPCC (Non-governmental International Panel on Climate Change).  While many national science academies and organizations still cling to the ever-changing "evidence" presented by the IPCC, it may be significant that the Chinese Academy of Sciences has translated and published a condensation of NIPCC reports.  

In the words of physicist Prof Howard "Cork" Hayden:

"If the science were as certain as climate activists pretend, then there would be precisely one climate model, and it would be in agreement with measured data.  As it happens, climate modelers have constructed literally dozens of climate models.  What they all have in common is a failure to represent reality, and a failure to agree with the other models.  As the models have increasingly diverged from the data, the climate clique have nevertheless grown increasingly confident -- from cocky in 2001 (66% certainty in IPCC's Third Assessment Report) to downright arrogant in 2013 (95% certainty in the Fifth Assessment Report)."

Climate activists seem to embrace faith and ideology -- and are no longer interested in facts.

S. Fred Singer is professor emeritus at the University of Virginia and director of the Science & Environmental Policy Project.  His specialty is atmospheric and space physics.  An expert in remote sensing and satellites, he served as the founding director of the US Weather Satellite Service and, more recently, as vice chair of the US National Advisory Committee on Oceans & Atmosphere.  He is a senior fellow of the Heartland Institute and the Independent Institute, and an elected Fellow of several scientific and engineering organizations.  He co-authored the NY Times best-seller Unstoppable Global Warming: Every 1500 years.  In 2007, he founded and has since chaired the NIPCC (Nongovernmental International Panel on Climate Change), which has released several scientific reports [See www.NIPCCreport.org].    For recent writings, see http://www.americanthinker.com/s_fred_singer/ and also Google Scholar.