On Consensus

The problem with several Climate Change denier arguments is that they are “meta” arguments – philosophical arguments about how people behave, what they intend and how things are done.

One such issue that they take is with the Intergovernmental Panel on Climate Change (IPCC) “consensus” method of operation. They seem to view the IPCC consensus as “blurred lines” – their conclusion is that the IPCC’s unified interpretation of the evidence is suspect.

When the Police want to interview eye-witnesses, and when a judge wants to hear witness evidence, the standard practice is to keep the witnesses apart, so that the lines of evidence can be as independent as possible.

By contrast, in Climate Change Science, there is a certain amount of collaboration between researchers during the course of their work, so you could say that no observations are made independently. However, this should not be labelled as “malicious collusion”, although many Climate Change deniers do do that.

In any particular dataset there may be issues of standardisation. Some satellites, for example, have had tracking errors which needed to be corrected. However, there are many lines of evidence, collected and collated by distinctly different groups, working on different areas.

Also, research articles are drawn up independently – the result being that there are often several different conjectures on the reasons for certain effects evidenced.

The IPCC reviews the most recent work in all the areas of research into Climate Change and synthesises the results.

The way that the IPCC works is that nothing appears in the final report unless it is accepted generally by the widely-spread team of reviewers, or is balanced by other opinion.

The normal case is that for those areas of the Science that are not sufficiently settled, or there has been abundant discussion in the scientific literature, the IPCC includes discussion of the varying results and opinions.

It may come as a shock for Climate Change deniers to know that well-known sceptics Ross McKitrick and Patrick Michaels have work on the Urban Heat Island effect reviewed in the IPCC report, as this was considered a valid piece of research.

The balance of evidence took the conclusions away from Ross McKitrick’s and Pat Michaels’ conclusions, however :-


For those findings of Science that are universally accepted by people with relevant knowledge, there is description, but often no discussion, as it is unnecessary.

However, this does not mean that the IPCC work is intolerant of other opinion. If there is other valid opinion, then it is discussed.

The challenge, surely, is to ask the Climate Change deniers to come up with some peer-reviewed, vindicated research that unsettles accepted Science instead of conducting a war of attrition in the blogosphere.

The “consensus” we see in the IPCC reports is a conservative agreement on what should be included – if any reviewer has been unable to accept something, and there is not alternative opinion with which to contrast it, or there has been no resolution in the scientific literature, it becomes categorised as “uncertain”, or is left out altogether from projections.

This is sometimes noted, as in the IPCC’s Fourth Assessment Report detailing sea level rises where the calculations on contributions to sea level rise projected from measurements of various kinds of melting ice were excluded, and the exclusion noted explicitly :-

Table 3.1 : “Model-based range excluding future rapid dynamical changes in ice flow”

If on the other hand there is strong agreement on what the empirical data is telling us, then this becomes a “robust” finding in the report.

A short summary is here :-


This is rigorous review of rigorous science.

So you see, IPCC consensus is good, not bad.

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