by Judith Curry

In our view, the fact that so many scientists agree so closely about the [causes of the] earth’s warming is, itself, evidence of a lack of evidence for [human caused] global warming. – D. Ryan Brumberg and Matthew Brumberg

The latest nonsensus on consensus from Cook, Oreskes et al. has been published [link]. The title ‘Consensus on consensus’ pretty much sums up what the paper is about — they claim that the combined weight of all the climate consensus papers that finds >90% agreement by scientists should convince us that ‘97%’ is robust.

I have criticized the idea of the 97% consensus many times [link], and I will leave it to others to critique this latest paper.

In this post I focus on the paradox of the climate consensus, as articulated in a blog post by D. Ryan Brumberg and Matthew Brumberg entitled The Paradox of Consensus. Excerpts:

Consensus, in and of itself, is not necessarily a bad thing. The more easily testable and verifiable a theory, the less debate we would expect. But as a question becomes more complex and less testable, we would expect an increasing level of disagreement and a lessening of the consensus. On such topics, independent minds can—and should—differ.

We can use a simple formula to express how an idea’s popularity correlates with its verifiability. Let us introduce the K/C ratio—the ratio of “knowability,” a broad term loosely encapsulating how possible it is to reduce uncertainty about an idea’s correctness, to “consensus,” a measure of the idea’s popularity and general acceptance. Topics that are easily knowable (K ~ 1) should have a high degree of consensus (C ~ 1), whereas those that are impossible to verify (K ~ 0) should have a low degree of consensus (C ~ 0). When the ratio deviates too far from the perfect ratio of 1, either from too much consensus or too little, there is a mispricing of knowledge. Indeed, in cases of extreme deviations from the perfect ratio, additional support for a concept with such a lopsided K/C ratio increasingly subtracts from its potential veracity. This occurs because ideas exist not simply at a single temporal point, but rather evolve over the sweep of time. At the upper reaches of consensus, there is less updating of views to account for new information—so much so that supporters of the status quo tend to suppress new facts and hypothesis. Government agencies deny funding to ‘sham’ scientists, tenure boards dissuade young researchers from pursuing ‘the wrong’ track, and the establishment quashes ‘heretical’ ideas. Too high consensus (skewed K/C ratio) inhibits the ability of an idea to evolve towards truth.

While not always clear why the K/C ratio can become highly skewed, one interpretation is that more than just the search for knowledge is at play.

The scope of agreement achieved by the world’s climate scientists is breathtaking. To first approximation, around 97% agree that human activity, particularly carbon dioxide emissions, causes global warming. So many great minds cannot possibly be wrong, right?

Yet something nags us about this self-congratulatory consensus. Our intuition is that this narrow distribution of opinions yields a knowability to consensus ratio far removed from the perfect ratio of 1. To reach their conclusions, climate scientists have to (a) uncover the (historical) drivers of climate, (b) project the future path of these inputs and others that may arise, and (c) predict how recursive feedback loops interact over multi-decadal time horizons, all without being able to test their hypotheses against reality.

We would, therefore, expect this limit on empirical verifiability to birth widely divergent views on the path, causes, and consequences of earth’s future climate. In other arenas, only after a theory has been empirically verified has the scientific community coalesced around it. Even then, scientists continue to subject such theories to rigorous testing and debate.

Yet the expectation of a rich debate among scientists about climate change does not reconcile easily with the widely endorsed shibboleth that human activity will warm the globe dramatically and dangerously over the next one hundred years. Any discussion that doubts the fundamental premises of climate change is dismissed by the mainstream media and climate scientists as pseudo-science conducted by quacks or ideologues.

In our view, the fact that so many scientists agree so closely about the earth’s warming is, itself, evidence of a lack of evidence for global warming. Does this mean that climate change is not happening? Not necessarily. But it does mean that we should be wary of the meretricious arguments mustered in its defense.

JC reflections

This essay provides an important insight in the K/C ratio — the ratio of knowability to consensus.

There is genuine scientific consensus on the following points:

global temperatures have increased overall since 1880

humans are contributing to a rise in atmospheric CO2 concentrations

CO2 emits and absorbs infrared radiation

For the most consequential issues, there remains considerable debate:

whether the warming since 1950 has been dominated by human causes

how much the planet will warm in the 21st century

whether warming is ‘dangerous’

whether radically reducing CO2 emissions will improve the climate and human well being

Leveraged by the consensus on the three points above that are not disputed, the climate ‘consensus’ is being sold as applying to all of the above, even the issues for which there remains considerable debate.

For past a certain point, each increase in the level of consensus makes it more difficult for new information to surface, thereby lowering the veracity we should assign to it.

The skewed scientific ‘consensus’ does indeed act to reinforce itself, through a range of professional incentives: ease of publishing results, particularly in high impact journals; success in funding; recognition from peers in terms of awards, promotions, etc.; media attention and publicity for research; appeal of the simplistic narrative that climate science can ‘save the world’; and a seat at the big policy tables.

The net result of this skewed ‘consensus’ is that inadequate attention is being paid to natural climate variability, and too many people, including scientists, assume that CO2 is a giant control knob that, if reduced, can eliminate bad weather, sea level rise, etc.

While not always clear why the K/C ratio can become highly skewed, one interpretation is that more than just the search for knowledge is at play.

Apart from the professional incentives described above, there are a range of political drivers that incentivize the consensus, including broad environmentalism, anti-fossil fuel sentiments, anti-capitalism sentiments, and a desire for world government that transcends national policies.

And finally, there is the seductiveness of identifying a simple cause of all of society’s problems, and a simple solution.

I think the Brumbergs are correct to conclude:

In our view, the fact that so many scientists agree so closely about the [causes of the] earth’s warming is, itself, evidence of a lack of evidence for [human caused] global warming.

Eliciting the opinion of experts is worthwhile, but it is important to clearly delineate which ‘experts’ should count:

There must be a sufficient number of others who did arrive (and continue to arrive) at the same conclusion through independent verification and testing.

A substantial majority of the individuals responding to the ‘expert’ surveys have not contributed to the primary literature on detection and attribution and have not conducted an independent assessment of this issue. Instead they have arrived at their conclusion based on the second-order evidence that a ‘consensus’ exists.

This consensus that has been manufactured by the IPCC in response to perceived desires of policy makers “makes it more difficult for new information to surface, thereby lowering the veracity we should assign to it.”

So, what have Cook, Oreskes et al. accomplished with their new paper? They are further reinforcing a very skewed consensus that is not defensible based upon our knowledge base.