Confusion, Consensus and Robust Policy Options

December 8th, 2004

Posted by: Roger Pielke, Jr.

“Consensus science can provide only an illusion of certainty. When consensus is substituted for a diversity of perspectives, it may in fact unnecessarily constrain decision-makers’ options.”

Naomi Oreskes, a scholar who I have a lot of respect for, caused a stir last week when she published an article in Science making the shocking claim that the consensus reflected in the Intergovernmental Panel on Climate Change (IPCC) appears to reflect, well, a consensus.

Like others, I think that it is clear Oreskes’ claim that there are no papers in the climate literature that disagree with the consensus is simply wrong. In fact, logically, this would have to be the case. The word “consensus” means “the judgment arrived at by most of those concerned”. Most is not all. The word “unanimity” means, “having the agreement and consent of all.” I have seen in email traffic a claim made that there are some 11,000+ articles on “climate change” referenced in the ISI database, and of these about 10% somehow contradict the consensus position.

But so what?


If that number is more like 1% or more like 40% it doesn’t seem to me to make any difference whatsoever from the standpoint of policy action. Of course, one has to be very careful using the imprecise phrase “policy action” because people tend to read into that a particular course of action that they themselves advocate. So let me be very clear. In the IPCC one can find statements to use in arguing for support of the Kyoto Protocol. But as well, in the IPCC one can find statements to use in arguing against supporting the Kyoto Protocol. And the same is true for any specific course of action on climate change. The IPCC does not point to, support, or lend credence to any single course of action. There is without a doubt an infinite array of policy options on climate change consistent with the knowledge represented in the IPCC.

So in addition to arguing about the science of climate change as a proxy for open policy debate, we now can add to that arguments about the notion of consensus on the science itself as a proxy for open political debate. My perspective is that neither of these debates should matter, are both a distraction from progress on climate change and a reflection of the tendency of all involved in the debates to politicize climate science. The actions that we take on climate change should be robust to (a) the diversity of scientific perspectives, and (b) the diversity of perspectives of the nature of the consensus. A consensus is measure of central tendency, but it necessarily has a distribution of perspectives around that central measure, and almost all of this distribution is well within the bounds of legitimate scientific debate. Our policies should not be optimized to reflect a single measure of central tendency, but instead, to be robust enough to accommodate the distribution of perspectives around that central measure, thus providing a bit of a buffer against the possibility that we might learn more in the future (on this see the excellent work of Rob Lempert).

For more on my perspective read this essay: Pielke, Jr., R. A., 2001: Room for doubt. Nature, 410:151.

Here is an excerpt from that essay:

“Consider once again global climate change. For many years, policy debate has centred on the degree of certainty that decision-makers ought to attach to competing visions of the future climate. Lost in this doomed enterprise is the point that climate will certainly have an increasingly strong effect on the environment and society, simply because of growing vulnerability related to factors such as population, wealth and use of land. If a goal of climate policy is to reduce the effects of climate on the environment and society, then effective action need not wait until we are more certain about details.

Seen in this light, efforts to reduce uncertainty via ‘consensus science’ – such as scientific assessments – are misplaced. Consensus science can provide only an illusion of certainty. When consensus is substituted for a diversity of perspectives, it may in fact unnecessarily constrain decision-makers’ options. Take for example weather forecasters, who are learning that the value to society of their forecasts is enhanced when decision-makers are provided with predictions in probabilistic rather than categorical fashion and decisions are made in full view of uncertainty. As a general principle, science and technology will contribute more effectively to society’s needs when decision-makers base their expectations on a full distribution of outcomes, and then make choices in the face of the resulting – perhaps considerable – uncertainty.”

One Response to “Confusion, Consensus and Robust Policy Options”

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  1. Timo Hämeranta Says:

    Roger Pielke Jr. ignores that within natural sciences new findings replace old ones.

    E.g. the IPCC TAR 2001 is already obsolete.

    Political consensus always drags along, badly, and therefore all political actions are always obsolete, too.

    See “The SCIENTIFIC BASIS of PREVAILING CLIMATE CHANGE ACTIONS and CLIMATE POLICIES in EU are OBSOLETE” online http://personal.inet.fi/koti/hameranta/euoncc.htm

    Best wishes

    Timo Hämeranta