Michael Mann’s narrow definition of “Skepticism”

Climate Scientist MM continues his dogged defence of the climate consensus at Thinkprogress.

Consider the following statement

Make no mistake: Skepticism is fundamental to good science. Whenever a conclusion is drawn or a proposition is made, the demand that it stand up to scrutiny is the self-correcting machinery that drives us towards a better understanding of the way the world works. In this sense, every scientist should be a skeptic. Good science responds to good faith challenges, and to contradictory evidence that is presented, and climate-change science should be no different.

The spirit of the following statement is at first beguiling, and the spirit is something that many would agree with, although “good faith challenges” allows for discrimination against people you disagree with. However, it is his meaning of “scepticism” that I want to take issue with here.

Mann’s definition is most clearly expressed by John Cook of “Skeptical Science“, but also supported by (amongst others) Tamino of “Open Mind” blog. The clearest expression is in the article “Are you a genuine skeptic or a climate denier?

Genuine skeptics consider all the evidence in their search for the truth. Deniers, on the other hand, refuse to accept any evidence that conflicts with their pre-determined views.

Compare this with a more established source of word definitions – the Oxford English Dictionary. I don’t have the full 20 volume edition, but I think my 1983 book club edition of the Shorter OED will do well enough. There are a number of definitions of “sceptic” on page 1900.

Definition 1 pertains to a school of philosophy after the Greek Pyrrho, which doubts the possibility of knowledge of any kind.

Definition 2 is someone who doubts the validity of knowledge claims in a particular area of inquiry. This includes, but is not confined to the natural sciences. In the area of climate is the Climate Realists like Tallbloke, who doubt the greenhouse gas theory.

Definition 2.1 “one who maintains a doubting attitude with reference to a particular question or statement“. The OED has this as the popular definition.

Definition 3 is one who doubts the truth of Christianity. An older definition, not applicable here.

Definition 4 is one who is seeking the truth. That is “an inquirer who has not arrived at definite convictions“. This is only occasionally used, at least in the late 20th century.

Cook’s definition is at odds with all the definitions in the dictionary. There is nothing there about how much evidence a genuine skeptic must consider. Indeed, it by his own definition Cook is not a skeptic. More seriously, Cook is disagreeing with the experts in their field. According to Cook’s definition, a skeptic is someone who formerly had a doubting attitude as in 2.1, but now has fallen into line. The philosophers are a school of deniers. (Desmogblog will no doubt now unearth evidence that they were in the pay of big olive oil producers.) Some who still doubts the truth of climate change will not have “considered all the evidence” yet. For those who have read the evidence, this category ceases to exist. The doubter of Christianity is irrelevant, whilst the seeker of truth is someone who is behind the curve.

But then who do you believe on the definition of “skeptic / sceptic”. A consensus of the world’s leading experts, or a group of dogmatic people using language for partisan purposes?

NB. I use sceptic with a “c” to denote the expert definition, and with a “k” to define the partisan definition. However, I quite realise the use of “c” was probably as a result of King George III trying the separate Britain from the revolting colonies by means of a common language.

With respect to Dr Mann, I may have got him totally wrong. Maybe he does not realise that skepticalscience.com is based on a misrepresentation. If Dr Mann (or a nominated associate) would like to clarify that he follows expert opinion, I will be more than happy to distance him from the polemicists who allegedly support him.

Aerosols – The UNIPCC AR4 adjustment factor

Scientific effort should be dedicated towards resolving the biggest unknowns. After feedbacks, the largest area of uncertainty in forecasting future global warming is the measurement of radiative forcing components.

A quick analysis of the radiative forcing components table in the 2007 AR4 Summary Figure 2.4, page 17 (4.1MB pdf) , would suggest a number of fudge factors have been used to arrive at the results.

I have summarised the table below, less the fancy bars, but with the uncertainty spreads and some check totals.

Radiative Forcing Components
Derived from AR4 (accessed March 2012)

RF Effect (W m-2)

Forcing Component Mid-point



Spread %

Carbon Dioxide










Nitrous Oxide










Ozone – Stratospheric





Ozone – Tropospheric





Stratospheric water vapour from CH4





Surface Albedo – Land Use





Surface Albedo – Black Carbon on Snow





Aerosol – Direct effect





Aerosol – Cloud lbedo effect





Linear Contrails





Net total





Of which:-
Positive Forcings





Negative Forcings





Assymetric Summing





Total per the Report





If these were financial figures, an external auditor might ask the following questions.

  1. Why do the columns not add up? The difference of 0.12 is the same as the figure for solar irradiance. I would guess that the error in the mid-point is due to someone having deducted this figure from the total, erroneously believing that they had previously included it.
  2. Given the breadth of uncertainty, is it more than a coincidence that the negative forcings almost exactly offset all the positive forcings with the exception of CO2? This conveniently reduces the language of the debate from discussing “anthropogenic greenhouse gases”, to “rising CO2”.
  3. Given the breadth of uncertainty, is it more than a coincidence that the range of negative forcings are exactly equal to 200% of the sum of the mid-points?
  4. Given the breadth of uncertainty, is it more than a coincidence that the range of postive forcings are almost exactly equal to 40% of the sum of the mid-points? Adjust any of the figures by .01, and the result becomes less exact.

This is an important issue, as this situation doubly increases the influence of CO2 on future warming. Firstly, it is the anthropogenic greenhouse gas that is consistently increasing. Others, like methane, levels, have stablised. Secondly, aerosols are likely to decrease in the future as countries develop and clean air legislation is enacted. Given the huge uncertainties in the other forcings, and possible fudge factors employed, it is possible that the significance of CO2 could be over-estimated a number of times. This is before water vapour feedbacks are considered.

Update June 3rd 2012.

Comparing with a paper published by James Hansen et al. in 2000, gives further circumstantial support to the fudge factors being employed.