Climate change: no consensus on consensus

Source: Climate Etc.

Judith Curry

by Judith Curry

The manufactured consensus of the IPCC has had the unintended consequences of distorting the science, elevating the voices of scientists that dispute the consensus, and motivating actions by the consensus scientists and their supporters that have diminished the public?s trust in the IPCC.

Our paper has just been accepted for publication.  A link to the final manuscript is provided here [consensus paper revised final].  Below is a ?reader?s digest? version of the main arguments made in this paper


The United Nations initiated a scientific consensus building process with the objective of providing a robust scientific basis for climate policy, under the auspices of the Intergovernmental Panel for Climate Change (IPCC). The key IPCC consensus finding from its latest assessment report is this statement:

?Most of the observed increase in global average temperatures since the mid-20th century is very likely due to the observed increase in anthropogenic greenhouse gas concentrations.?

The IPCC consensus findings on attribution have been echoed in position statements made by many scientific organizations. The IPCC consensus is portrayed as nearly total among scientists with expertise and prominence in the field of climate science. The idea of a scientific consensus surrounding climate change attribution has been questioned by a number of people, including scientists and politicians. Much effort has been undertaken by those that support the IPCC consensus to discredit skeptical voices, essentially dismissing them as cranks or at best rebels, or even politically motivated ?deniers?.

Students of science are taught to reject ad populam or ?bandwagon? appeals, a sentiment is articulated by the motto of the UK Royal Society: ?nullius in verba?, which is roughly translated as ?take nobody?s word for it?.  How then, and why, have climate scientists come to a scientific consensus about a very complex scientific problem that the consensus-supporting scientists themselves acknowledge has substantial and fundamental uncertainties?

Consensus and dissent

The debate surrounding the consensus on climate change is complicated by the complexity of both the scientific and the associated sociopolitical issues.  Underlying this debate is a fundamental tension between two competing conceptions of scientific inquiry: the consensual view of science versus the dissension view.  Under the consensual approach, the goal of science is a consensus of rational opinion over the widest possible field.  The opposing view of science is that of dissension, whereby scientific progress occurs via subversion of consensus in favor of new experiments, ideas and theories.

When is it reasonable for a person to conform to a consensus and when is it reasonable to dissent?

With genuinely well-established scientific theories, ?consensus? is not discussed and the concept of consensus is arguably irrelevant.  For example, there is no point to discussing a consensus that the Earth orbits the sun, or that the hydrogen molecule has less mass than the nitrogen molecule.  While a consensus may arise surrounding a specific scientific hypothesis or theory, the existence of a consensus is not itself the evidence.

The issue of challenges to the IPCC consensus statement on attribution is not analogous to Galileo-like revolutionaries.  Rather these challenges are associated with a concern about the oversimplification by the IPCC of a complex issue in the interests of policy making.  How to reason about uncertainties in the complex climate system and its computer simulations is neither simple nor obvious. Scientific debates involve controversies over the value and importance of particular classes of evidence as well as disagreement about the appropriate logical framework for linking and assessing the evidence. The IPCC faces a daunting challenge with regards to characterizing and reasoning about uncertainty, assessing the quality of evidence, linking the evidence into arguments, identifying areas of ignorance and assessing confidence levels.  An overarching concern is how the issue of climate change is framed scientifically and how judgments about confidence in complex scientific arguments are made in view of the cascade of uncertainties.

Given the complexity of the climate problem, ?expert judgments? about uncertainty and confidence levels are made by the IPCC on issues that are dominated by unquantifiable uncertainties. It is difficult to avoid concluding that the IPCC consensus is manufactured and that the existence of this consensus does not lend intellectual substance to their conclusions.

Consensus and bias

If the objective of scientific research is to obtain truth and avoid error, how might a consensus seeking process introduce bias into the science and increase the chances for error?  ?Confirmation bias? is a well-known psychological principle that connotes the seeking or interpreting of evidence in ways that are partial to existing beliefs, expectations, or an existing hypothesis. Confirmation bias usually refers to unwitting selectivity in the acquisition and interpretation of evidence.

Princeton philosopher Thomas Kelly provides some insight into confirmation bias, arguing that a prior belief can skew the total evidence that is available subsequently in a direction that is favorable to itself. Kelly also finds that individuals tend to be significantly better at detecting fallacies when the fallacy occurs in an argument for a conclusion which they disbelieve, rather than for a conclusion in which they believe.  Kelly identifies a further source of confirmation bias in the consensus building process, whereby as more and more peers weigh in on the issue, the higher order psychological evidence of what others believe can eventually swamp the first order evidence into virtual insignificance.

With regards to the IPCC, cognitive biases in the context of an institutionalized consensus building process have arguably resulted in the consensus becoming increasingly confirmed in a self-reinforcing way, to the detriment of the scientific process.

Role of scientific consensus in decision making

The mandate of the IPCC is to provide policy?relevant information to policy makers involved in the UN Framework Convention on Climate Change (UNFCCC).  Based upon the precautionary principle, the UNFCCC established a qualitative climate goal for the long term: avoiding dangerous climate change by stabilization of the concentrations of atmospheric greenhouse gases. The IPCC scientific assessments play a primary role in legitimizing national and international policies aimed at reducing greenhouse gas emissions. The main practical objective of the IPCC has been to assess whether there is sufficient certainty in the science so as to trigger political action to reduce greenhouse gas emissions. This objective has led to the IPCC assessments being framed around identifying anthropogenic influences on climate, environmental and socio-economic impacts of climate change, and stabilization of CO2 concentrations in the atmosphere.

This relationship between expertise and policy is described as the linear model of expertise, or ?speaking truth to power?, whereby first science has to ?get it right? and then policy comes into play. The influence of science on policy is assumed to be deterministic: if the scientific facts are ?sound,? then they have a direct impact on policy. In the linear model, the key question is whether existing scientific knowledge is certain enough, or there is a consensus of experts, to compel action.

Dutch social scientist Jeroen Van der Sluijs argues that the IPCC has adopted a ?speaking consensus to power? approach that sees uncertainty and dissent as problematic, and attempts to mediate these into a consensus.  The ?speaking consensus to power? strategy acknowledges that available knowledge is inconclusive, and uses consensus as a proxy for truth through a negotiated interpretation of the inconclusive body of scientific evidence. The ?consensus to power? strategy reflects a specific vision of how politics deals with scientific uncertainties and endeavors to create a  knowledge base for decision making following the linear model of expertise.

The linear model of expertise works well for ?tame? problems, where everyone essentially   agrees on both the problem and the solution.  Successes in managing tame problems are evident in the domains of engineering and regulatory science.  Climate change has been framed by the UNFCCC/IPCC as a relatively ?tame? problem that requires a straightforward solution, namely the top-down creation of a global carbon market. However, climate change is arguably characterized better as a ?wicked problem? or a ?mess?. ?Messes? and ?wicked problems? are characterized by multiple problem definitions, methods that are open to contention and solutions that are variable and disputed, and  ?unknown unknowns? that suggest chronic conditions of ignorance and lack of capacity to imagine future eventualities of both the problem and the proposed solutions.

Unintended consequences of the IPCC consensus

The consensus approach used by the IPCC has received a number of criticisms. Concerns have been raised about the need to guard against overconfidence and overemphasize expected outcomes. The consensus approach being used by the IPCC has failed to produce a thorough portrayal of the complexities of the problem and the associated uncertainties in our understanding, in favor of spuriously constructed expert opinion. Further, concerns are being raised that the IPCC?s consensus claim is distorting the science itself, as scientists involved in the IPCC process consider the impact of their statements on the ability of the IPCC to defend its previous claims of consensus.

While the IPCC?s consensus approach acknowledges uncertainties, defenders of the IPCC consensus have expended considerable efforts in the ?boundary work? of distinguishing those qualified to contribute to the climate change consensus from those who are not.  These efforts have characterized skeptics as small in number, extreme, and scientifically suspect.   These efforts create temptations to make illegitimate attacks on scientists whose views do not align with the consensus, and to dismiss any disagreement as politically motivated ?denialism?. The use of ?denier? to label anyone who disagrees with the IPCC consensus on attribution leads to concerns being raised about the IPCC being enforced as dogma, which is tied to how dissent is dealt with.

The linear model of expertise places science at the center of political debate. Scientific controversies surrounding evidence of climate change have thus become a proxy for political battles over whether and how to react to climate change. Therefore, winning a scientific debate results in a privileged position in political battle, hence providing motivation for defending the consensus. As a result, it has become difficult to disentangle political arguments about climate policies from scientific arguments about the evidence for human-induced climate change. The quality of both political debate and scientific practice can suffer as a consequence.

The linear model of expertise ?speaking consensus to power? tends to stifle discussion of alternative policy approaches. The IPCC has framed its assessment around the UNFCCC policy of stabilizing greenhouse emissions, focusing its scientific assessment on the attribution of climate change and the sensitivity of climate change to greenhouse gases. The narrow focus on issues of attribution masks major political implications, marginalizes issues around adaptation and development, and fails to engage with alternative approaches and to generate ideas to inform its ?solutions?.

While the public may not understand the complexity of the science or be predisposed culturally to accept the consensus, they can certainly understand the vociferous debates over the science portrayed by the media.   Further, they can judge the social facts surrounding the consensus building process, including those revealed by the so-called ?Climategate? episode, and decide whether to trust the experts whose opinion comprises the consensus.

In summary, the manufactured consensus of the IPCC has arguably had the unintended consequences of distorting the science, elevating the voices of scientists that dispute the consensus, and motivating actions by the consensus scientists and their supporters that have diminished the public?s trust in the IPCC.

Ways forward

The linear model of climate science expertise conceals uncertainties, ambiguities, dissent and ignorance behind a scientific consensus. The most important actions that are needed with regards to climate science ? particularly in context of the IPCC assessment reports ?  are explicit reflection on uncertainties, ambiguities and areas of ignorance (both known and unknown unknowns) and more openness for dissent in the IPCC processes.  Greater openness about scientific uncertainties and ignorance, and more transparency about dissent and disagreement, would provide policymakers with a more complete picture of climate science and its limitations. In the context of iterative risk management, policy makers need insight into the rate of learning, as well as what is known and unknown.

Moving forward requires a reassessment of the ?consensus to power? approach for the science-policy interface that has evolved in the context of the IPCC and UNFCCC. The challenge is to open up the decision making processes in a way that renders their primary nature more honestly political and economic, while giving proper weight to scientific reason and evidence.

There are frameworks for decision making under deep uncertainty and ignorance that accept uncertainty and dissent as key elements of the decision making process.  Rather than choosing an optimal policy based on a scientific consensus, decision makers can design robust and flexible policy strategies that account for uncertainty, ignorance and dissent.  Robust strategies formally consider uncertainty, whereby decision makers seek to reduce the range of possible scenarios over which the strategy performs poorly.  Flexible strategies are adaptive, and can be quickly adjusted to advancing scientific insights.


The climate community has worked for more than 20 years to establish a scientific consensus on anthropogenic climate change.  Perspectives from multiple disciplines support the inference that the scientific consensus seeking process used by the IPCC has had the unintended consequence of introducing biases into the both the science and related decision making processes. The IPCC scientific consensus has become convoluted with consensus decision making through a ?speaking consensus to power? approach.  The growing implications of the messy wickedness of the climate change problem are becoming increasingly apparent, highlighting the inadequacies of the ?consensus to power? approach for decision making on the complex issues associated with climate change. Further, research from the field of science and technology studies are finding that manufacturing a consensus in the context of the IPCC has acted to hyper-politicize the scientific and policy debates, to the detriment of both.  Arguments are increasingly being made to abandon the scientific consensus seeking approach in favor of open debate of the arguments themselves and discussion of a broad range of policy options that stimulate local and regional solutions to the multifaceted and interrelated issues of climate change, land use, resource management, cost effective clean energy solutions, and developing technologies to expand energy access efficiently.

JC comment:  The paper has been published in a new online journal, CAB Reviews.  My reasons for publishing in this journal are that CAB Reviews invited me to write the article and suggested the topic, it exposes me to a new audience, and it avoids the partisan sniping of publishing a paper like this in a climate-related journal.  I have to say that I was enormously pleased by the editorial handling of this manuscript, and the reviews contributed to improving the paper.  One reviewer self identified as a historian of science, and the other seemed to be in the field of science and technology studies; both had substantial familiarity with the topic of climate science.  Interestingly, the most controversial sections in the opinions of both reviewers were the Introduction and section on Consensus and the Philosophy of Science.

I?m experimenting with a new format for blogging about my published papers, by providing a reader?s digest version, let me know if you think this is effective (I hope that some of you will read the entire paper).

This is a technical thread; please keep your comments relevant.