http://www.bishop-hill.net/blog/201...aims-of-significant-temperature-rise-unt.html
The second paragraph gives the relative likelihood of the trending autoregressive model with respect to the driftless model. The relative likelihood is 0.08, if we analyze years 1900â2012 , and it is 0.001, if we analyze years 1850â2012 (using Met Office data). In either case, then, the trending autoregressive model is much less likely than the driftless model to be the better model of the data. Hence, the statistical model that was relied upon in the Answer to the original Question (HL3050) is untenable.
Most of the third paragraph is verbiage. In particular, the cited âphysical climate modelsâ, which the Met Office runs on its supercomputer, do indeed provide some evidence for global warming. Physical climate models and statistical models are both known as âmodelsâ, but they are different things. It is only the statistical models that are relevant to the Question. The physical climate models, though impressive in many ways, do not provide observational evidence for global warming.
The issue here is the claim that âthe temperature rise since about 1880 is statistically significantâ, which was made by the Met Office in response to the original Question (HL3050). The basis for that claim has now been effectively acknowledged to be untenable. Possibly there is some other basis for the claim, but that seems extremely implausible: the claim does not seem to have any valid basis.
Plainly, then, the Met Office should now publicly withdraw the claim. That is, the Met Office should admit that the warming shown by the global-temperature record since 1880 (or indeed 1850) might be reasonably attributed to natural random variation. Additionally, the Met Office needs to reassess other claims that it has made about statistically significant climatic changes.
Lastly, it is not only the Met Office that has claimed that the increase in global temperatures is statistically significant: the IPCC has as well. Moreover, the IPCC used the same statistical model as the Met Office, in its most-recent Assessment Report (2007). The Assessment Report discusses the choice of model in Volume I, Appendix 3.A. The Appendix correctly acknowledges that, concerning statistical significance, âthe results depend on the statistical model usedâ.
What justification does the Appendix give for c
