Dr Gray seeks precision, and looks to ascribe precise meanings to the published statements. He points out however that precision is not what the reports offer.
The most pervasive example is the "equilibrium climate sensitivity", the rise in global temperature from a doubling of carbon dioxide concentration. The range of figures used by the IPCC 1.5ºC to 4.5ºC, was decided by "a show of hands" at an early meeting of "experts". The IPCC Reports are full of statements of how "confident" they are of model results, and how they are "improved" (over what?).RELATED: Global Warming, Science, Politics
They have developed a series of purely qualitative guesses to judge the model results, to which they have the cheek to assign statistical figures, as follows:
"In this Summary for Policymakers and in the Technical Summary, the following words have been used to indicate approximate judgmental estimates of confidence:virtually certain (greater than 99% chance that a result is true);These creative guesses are obtained from meetings of "experts" who are all people who depend for their livelihood on the success of their models. These figures cannot therefore be taken seriously.
very likely (90-99% chance);
likely (66-90% chance);
medium likelihood (33-66% chance);
unlikely (10-33% chance);
very unlikely (1-10% chance);
exceptionally unlikely (less than 1% chance)."
It is useful to consider the following statement of the IPCC (often regarded as a"conclusion") using these assessments."In the light of the new evidence and taking into account of remaining uncertainties, most of the observed warming over the last 50 years is likely to have been due to the increase in greenhouse gas concentrations...""most." not all, but how much?Let us look at the other IPCC statements.
"observed" "over the last 50 years" restricts it to the unreliable surface record.
"warming' "over the last 50 years" The "observed" temperature fell for the first half, from 1950 to 1976.
"likely" This means, as stated above, one chance in 3 to one chance in 10 that they are wrong.
"greenhouse gas concentrations" No mention of humans. The most important greenhouse gas is water vapour and nobody knows whether its concentration has increased or fallen."The balance of the evidence suggests a discernible human influence on global climate..."Then there is
"balance" This presumably means more than 50% probability.
"suggests" Who decided that this suggestion should be made? Biased scientists?
"discernible" but has it actually been DISCERNED?
"human influence" No mention of greenhouse gases."There is new and stronger evidence that most of the warming observed over the last 50 years is attributable to human activities..."Then, on top of that, is this statement from Chapter 1 of "Climate Change 2001"
"most" Above 50%?
"warming ... over the last 50 years" Restricted to the unreliable "surface record."
"warming ... over the last 50 years" For the first half (1950 to 1976) the temperature fell.
"attributable" but it has not actually been ATTRIBUTED, has it?
"human activities" which do not include emissions of greenhouse gases."The fact that the global mean temperature has increased since the late nineteenth century and that other trends havebeen observed does not necessarily mean that we have identified an anthropogenic effect on the climate system.Climate has always varied on all time scales, so the observed change may be natural."How can anybody claim that this mixture of pronouncements can be interpreted to mean that "the science is settled"?