Subjective elements in climate policy advice

Subjective elements are an inevitable component of scientific advice on climate policies. Good practice warrants that the level of assumption underlying subjective elements be parsimonious, that their effects on policy decisions be identified, and that policy relevant variables be communicated with appropriate levels of precision. In the case of climate sensitivity, the level of precision is intrinsically difficult to quantify. There is no ‘true’ value of climate sensitivity to be discovered. Rather, best practice consists of the application of multiple methods to estimate the quantity. Best practice provides confidence that some values of climate sensitivity are more likely than others. This lends support to the notion of weighting climate sensitivity values, though the appropriate precision appears to be less than that implied by use of a probability density function (pdf) and greater than that implied by use of a simple range. Use of both a pdf and a range in this case can provide information about likely outcomes and possible extremes.

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