(for the first part, visit “The IPCC Is Never Wrong -1- Why Kevin Trenberth Is Right“)
Given that the scientifically-valid statements in the IPCC AR4 report are strictly capable to cover and include whatever outcome the Earth’s climate will compute for us, how can we find ourselves surrounded by people clamoring that, on the basis of the very same IPCC report, the “science is settled”?
“Chinese whispers”. That’s how.
The incoming strictly-orthodox and yet very open minded IPCC message is of an ongoing, complex, fascinating scientific analysis full of uncertainties that need to be investigated. Yet, at the other end of the “broken telephone” all channels are clogged by absurdist, simplistic claims of “the debate is over” (a statement that is, in a sense, the true denial).
(ironically, even RealClimate has recognized there might be a communication problem…)
Take a look for example at the magnitude of the solar forcing, again according to the IPCC. The “official value” everybody with even a remote interest keeps hearing about, is 0.12 and can be found in AR4-WG1-Chapter2 (*), page 193.
But then if you go to page 212, Table 2.11, it turns out that the “level of scientific understanding” for Solar Irradiance is “Low”, and for the component linked to cosmic UV rays is “Very low”.
And that’s not even remotely enough. All the known unknowns about the role of the Sun in shaping the Earth’s climate are clearly spelled out in Joanna D. Haigh’s “The Sun and the Earth’s climate” (**). True, that article might have been published after the official IPCC deadline. On the other hand, Dr Haig was well known at the time to the IPCC authors and reviewers, and appears four times among the References for that chapter alone.
What has happened then? Go back to page 193. The text actually reads:
The best estimate is +0.12 W m-2 (90% confidence interval: +0.06 to +0.30 W m-2)
That means that actual value can be half, or 2.5 times as much, and that’s just considering a confidence interval of 90% (“moderately confident” in statistical jargon) rather than the classic 95% (regarding which the spread between minimum and maximum possible value would have obviously been considerably wider).
And so we find the IPCC “moderately confident” about a forcing whose (1) known known components are “little to very little” understood, (2) known unknown components are not even considered despite being present in the Literature and (3) unknown unknown components… (well, “no comment” about those).
Add to that the fact that a “forcing”, like all “forcings“, is not a measurable quantity in the real world, and therefore exists strictly as an estimate. An estimate about which the IPCC is somewhat ‘schizophrenic’ to say the least.
And yet, all that fun is not found anywhere: instead of “low to very low understanding” about an estimate done with “moderate confidence“, what we read is how small the Solar forcing “IS”: 0.12.
Onwards and upwards, as they used to say…
(*) Forster, P., V. Ramaswamy, P. Artaxo, T. Berntsen, R. Betts, D.W. Fahey, J. Haywood, J. Lean, D.C. Lowe, G. Myhre, J. Nganga, R. Prinn, G. Raga, M. Schulz and R. Van Dorland, 2007: Changes in Atmospheric Constituents and in Radiative Forcing. In: Climate Change 2007: The Physical Science Basis. Contribution of Working Group I to the Fourth Assessment Report of the Intergovernmental Panel on Climate Change [Solomon, S., D. Qin, M. Manning, Z. Chen, M. Marquis, K.B. Averyt, M.Tignor and H.L. Miller (eds.)]. Cambridge University Press, Cambridge, United Kingdom and New York, NY, USA.
(**) Joanna D. Haigh, “The Sun and the Earth’s Climate”, Living Rev. Solar Phys. 4, (2007), 2. URL (cited on Oct 14, 2009): http://www.livingreviews.org/lrsp-2007-2