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Consensus on consensus

Posted on 5 May 2016 by Andy Skuce

Originally published in Corporate Knights Magazine

In 1998 and 1999, American scientists Michael Mann, Raymond Bradley and Malcolm Hughes published two papers that reconstructed the average temperatures of the northern hemisphere back to the year 1000. The articles showed a temperature profile that gently declined from 1000 to 1850, fluctuating a little along the way, with a sudden increase in the late nineteenth and the twentieth centuries.  The graph was nick-named “the Hockey Stick”, with its long relatively straight handle showing the stable pre-industrial climate and the blade representing the sudden uptick in the last 150 years.

The diagram was a striking depiction of the abrupt warming that had occurred since the Industrial Revolution compared to what happened before. For those opposed to the scientific consensus on Anthropogenic Global Warming (AGW), the Hockey Stick posed a threat and had to be broken.

As detailed in Mann’s 2013 book The Hockey Stick and the Climate Wars: Dispatches from the Front Lines,his critics employed a variety of tactics to try to break the hockey stick. They disputed the statistical methods that Mann and his colleagues used, although they never produced new results of their own. Stolen private conversations were quote-mined for damning phrases. Senior US politicians and the right-wing press denounced the work a fraud.

Mann and other scientists were subjected to numerous investigations, all of which exonerated the Hockey Stick authors. Most importantly, other researchers, using alternative methods and new data, produced additional temperature curves that closely matched the original results of Mann et al. Nevertheless, the attacks on the original Hockey Stick continued, as has the harassment of Mann by right-wing pundits. If you need to deny the consensus on AGW, you have to keep repeating that the “Hockey Stick is Broken”. Never mind that it is intact and that there are enough new sticks to equip an NHL team.

There are parallels with the reception given to the paper Quantifying the consensus on anthropogenic global warming in the scientific literature, published in 2013 by University of Queensland researcher John Cook and eight volunteers associated with the website Skeptical Science (including me). The paper, published in the journal Environmental Research Letters (ERL), has been deemed a hoax and a fraud, by contrarian bloggers as well as by Republican presidential hopefuls such as Ted Cruz and Rick Santorum.

The most determined academic critic has been Dr Richard Tol, an econometrician at the University of Sussex. Tol is a prolific and widely-cited author on the economic impact of future climate change and is an advisor to the Global Warming Policy Foundation, a British organization opposed to taking action on climate change. Tol published a critique in 2014 in the journal Energy Policy, which I discussed previously at Corporate Knights.

The more you know the more you agree

Tol had made several attempts to publish a critical response in the ERL. After several rejections, the journal finally accepted a comment by Tol this year. Part of his new paper was a rehash of methodological quibbles that had been answered before. He made no estimate of how much these minor issues, even if they were valid, might affect the overall results.

Tol also surveyed the recent literature on consensus studies and claimed that the Cook et al study is an outlier. In an early draft of his article, which he put online before it was accepted by the journal, he grossly mischaracterized the results of several other studies, claiming that they had found low levels of scientific consensus. Dutch blogger Collin Maessen wrote to the authors of those articles and asked them what they thought of Tol’s manuscript. Here are samples of the reactions:

  • Naomi Oreskes (Harvard University): No it is not accurate. As usual, he [Tol] is misrepresenting scientific work, in this case mine.
  • William Anderegg (Princeton University): This is by no means a correct or valid interpretation of our results.
  • Bart Verheggen (Amsterdam University College): To claim, as Richard Tol does, that the outcome for this subsample is somehow representative of the scientific consensus is entirely nonsensical.

Reactions like these motivated the authors of those studies, from nine different universities in the US, UK and the Netherlands, to join the original volunteer team that worked on the 97 per cent paper in writing a rebuttal to Tol. This effort turned into a short review of several recent consensus research articles. It was published in ERL as an open-access paper on April 13 2016.

Examining fifteen different studies, we found that the results depended strongly on the exact question asked and the level of expertise of the scientists sampled. The more expert the group of scientists whose views were examined, the higher the level of consensus that recent global warming is man-made. Actively publishing climatologists are more in agreement than, for example, economic geologists. Consensus figures ranged from 90 to 100 per cent among the most expert climate scientists, with a clustering of results around 97 per cent: there is nothing exceptional about the Cook et al result.

The concluding sentence of the rebuttal paper reads:

From a broader perspective, it doesn’t matter if the consensus number is 90% or 100%. The level of scientific agreement on AGW is overwhelmingly high because the supporting evidence is overwhelmingly strong.

Although the 2013 Cook et al study has received the most attention, several other independent studies have reached the same general conclusions. There is a consensus that there is a strong consensus that humans are the primary cause of recent global warming.

John Cook has prepared a short video, explaining all of this:

Opening the gateway

In the wake of the Paris Agreement, in which 195 countries unanimously pledged to cut fossil fuel emissions, readers might well ask why measuring the consensus on AGW matters.

One problem is that the electorate of the United States is not strongly committed to the Paris goals. In particular, the Republican party, which controls both houses of Congress and a majority of state capitols, overwhelmingly denies that humans are a major cause of climate change.

A recent survey of school teachers in the U.S. found that although two-thirds of them accepted a major human role in recent global warming, less than half were aware of the overwhelming consensus among climate scientists. When so many teachers believe that there is a substantial minority of experts who doubt AGW, it is not surprising that they often adopt a “both sides” approach to teaching the subject. This gives a bogus veneer of credibility to anti-AGW views.

It has long been an effective tactic for conservative thought leaders to cast doubt on the scientific consensus of man-made climate change. This has resulted in the so-called “consensus gap”: the mismatch between perceptions of the degree of scientific consensus that exists among teachers and the public at large, and the very strong agreement within the expert community.

Recent research by Sander van der Linden  of Princeton University and two colleagues has demonstrated that communicating the true degree of consensus is an effective strategy in influencing opinions across the political spectrum. Indeed, they conclude that public perception of the scientific consensus is an important “gateway belief” that allows people who doubt the reality of man-made climate change to move from rejection to acceptance.

This has also important consequences for policy outside the U.S. In December 2015, the nations of the world agreed unanimously in Paris to an aggressive program to reduce greenhouse gas emissions to limit the increase in global average temperatures to 2 C above pre-industrial levels. However, that target needs to be translated into effective policies at national levels and that will require solid support among electorates who do not understand how solid the underlying scientific consensus is. Unlocking the gateway of doubt is essential if governments are to maintain public support and move from good intentions to success in halting global warming.

Firm foundations

The climate change “merchants of doubt” are unlikely to give up peddling spurious uncertainty messages any day soon. Politicians like Ted Cruz will continue to question the temperature record despite the fact that multiple studies have confirmed that the anomalies observed in 2014 and 2015 are the highest since measurements began. The doubters also seem unable to accept that the “Hockey Stick” graphs, which show that post-industrial global warming is unprecedented over the past two millennia, have been independently replicated several times.  Although multiple studies demonstrate that the overwhelming majority of climate scientists conclude that this exceptional recent warming is caused by humans, obstinate deniers will continue to insist, against all evidence, that the consensus on climate change is crumbling.

The scientific consensus on climate change is not founded on a single study. Instead, many research projects using independent methods arrive at similar results. It is these multiple lines of evidence that give the scientific community such strong confidence that humans are responsible for the recent unprecedented warming of the surface of the Earth. And it is on this solid bedrock that policy makers have to construct the strategies that will reduce the irreversible changes that we are making to the livability of the only home we have.

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Comments 1 to 6:

  1. And yet, as has been pointed out by climate sceptics and scientists, Consensis has very little to do with science.  Evidence does and the evidence is pretty overwhelming that the climate is changeing and we are resposible.  Perhaps we should leave this argument alone and just argue on the evidence.

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  2. Personally, I find the evidence very convincing, but there are lots of different kinds of people and not all of them are swayed by evidence. Numbers and physics just turns some people off. The consensus is a way to reach those people. We need to bring as many people as possible on board to solve this problem.

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  3. william@1,

    In case you've missed the point of this "consensus on consensus" study: it does not argue that consensus is the evidence of AGW (as your comment incorrectly implies). It does provide the statistical evidence that 97% consensus on AGW among climate scientists is not an outlier.

    You're correct that such study does not prove AGW. But you're incorrect that such study is useless. The study provides evidence to the wide public - i.e. those who rely of expert opinion because they are incapable or unwilling to spend time and effort to shape their own oipinion - that expert climate scientists publish solid & accurate knowledge. That every eveidence indicates climate expert opinions should be acknowledged as much (if not more than) the opinions of other science experts, like e.g. astronomers. Any "news" of conspiracy theories among climate scientists dissiminated dniers are pure. often evil falshood.

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  4. William.

    There is actually an evidence base for why consensus messaging is an important part of communication. It is evidence from psychology. Your argument has a basic assumption. That we are all rational, all of the time, and thus arguing the evidence about climate will work.

    When in reality, most of us most of the time are actually rather irrational. We use mental short-cuts, heuristics, quick gut-reactions, and all sorts of ways of forming a view of some sort with least effort. And we strongly filter what we hear based on our inner world-view, our value system, our fears and hopes. Difficult external knowledge can have a hard time sinking in when it conflicts with our prior ideas. And our minds are very good at doing all sorts of tricks and cognitive biases.

    So 'Just the facts Ma'am, just the facts' doesn't work so well when it is competing agaisnt our inner monologue.

    One important aspect of our biase-addled minds is that we follow the herd, want to fit in, want to be accepted by those around us. So we often tend to think what others think; it feels safer.

    This is the power of consensus messaging. It is saying to people, 'its alright, everyone else thinks this too'. So long as the scientific consensus is soundly based - which it is - there actually is no problem, and good reasons for using consensus messaging.

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  5. To further your basic point, Glenn:

    Edward DeBono wrote a book called mechanism of mind saying that the mistakes of the system were what made it work. (It's an old book so it might be wrong...!!??!)

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  6. A few thoughts about the importance of consensus.

    1. William – it seems to me that your comment is self-contradictory. You say

    a. Consensus has little to do with science.
    b. Evidence is essential to science.
    c. We should base our arguments on the evidence.

    The use of the term ‘we’ indicates consensus concerning the evidence. Without this consensus there is no we who, you say, are to base arguments on the evidence.

    The essence of science is the process of correction. As experiments are performed or as more data are gathered by a community of scientists, our understanding of physical processes increases, our instruments are improved and our measurements and our theories (i.e., models) become more precise.

    Science is a communal enterprise. If you fail to get colleagues in your field to understand your experiments and theories you are failing as a scientist. If your colleagues, assuming they have reputations as capable experimentalists, are unable to replicate your findings you are failing as a scientist. It doesn’t mean that, in the end, their judgments will not be revised. It does mean, however, that the judgments of the scientific community— i.e., the consensus judgments of that community are important to the process of the scientific enterprise.

    A certain measure of disagreement within the scientific community is sometimes helpful. Not all consensus or agreement is important. But deviate too far from the consensus views of this community : reject the importance of things such as measurements, experiments, data, and the use of mathematics and your ability to interact with the scientific community will come to an end. Science could not exist as an enterprise without shared views of the value of evidence, data, and instrumentation.

    BBHY –

    I am with you here. Evidence is only convincing if it is understood. I am not a scientist. I cannot claim to understand much at all beyond the introductory sentences of a science journal article.

    I am no more capable of looking at the evidence for warming and arguing that this evidence is sufficient warrant to show that humans are causing warming than I can look at my x-rays and other medical evidence and claim that I need xyz surgery. I leave it to the scientific and medical experts to come to their conclusions. I would be a fool to disagree with the consensus of the scientific or the medical community.

    William –

    I agree with you on your views about rationality, mental short-cuts, biases etc. But the problem runs deeper. It affects scientists too. You say our scientific consensus is soundly based. How to we ever know this? There is no simple instrument that registers positively when consensus is soundly based.
    How would we verify the accuracy of such an instrument?

    Right now, the scientific consensus on AGW is meeting very little opposition from credible sources. All objections to the consensus are coming from opponents based on their political and economic interests. None of the objections are coming from credible scientific sources.

    So, I would argue that we think that our scientific consensus is soundly based because we have a consensus concerning how to conduct scientific inquiry – we agree on the use of data, the use of various instruments to collect that data, the use of various mathematical methods to evaluate that data, and we agree on the importance of open inquiry. Based on this consensus concerning how the scientific enterprise to to be conducted we can form a meta-consensus about the well founded basis of climate science.

    Its not quite like turtles all the way down but it is turtles down a bit further than you suggest.

    My point is no more than consensus is important and perhaps more important than its been treated in the comments.

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