Has the Earth Experienced Statistically Significant Warming Since the Late 19th Century?

The answer to that question apparently is No, although you may need to be a statistician to fully appreciate Doug Keenan’s explanation. You don’t need any expertise in statistics, however, to follow the entertaining story of how the British government has bobbed and weaved in response to the Parliamentary Question, “whether they consider a rise in global temperature of 0.8 degrees Celsius since 1880 to be significant.”

The important news story is that the Met Office has recently admitted–although not in terms easily understandable by the layman–that the Earth’s warming since 1880 (assuming that can accurately be measured, which I doubt) is not statistically significant:

The statistical comparison of the model fits shows the likelihood of a linear trend model with first-order autoregressive noise in representing the evolution of global annual average surface temperature anomalies since 1900, ranges from 0.08 (Met Office data) to 0.32 (NOAA data), relative to the fit for a driftless third-order autoregressive integrated model. The likelihood is 0.001 if the start date is extended back for example to 1850 (Met Office data). These findings demonstrate that this parameter is very sensitive to the data period chosen and to the dataset chosen for a given time period, for such a statistical model.

Keenan explains:

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 1900–2012, and it is 0.001, if we analyze years 1850–2012 (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.

And this is the conclusion, expressed in non-technical terms:

[I]t 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, “the results depend on the statistical model used”.

What justification does the Appendix give for choosing the trending autoregressive model? None. In other words, the model used by the IPCC is just adopted by proclamation. Science is supposed to be based on evidence and logic. The failure of the IPCC to present any evidence or logic to support its choice of model is a serious violation of basic scientific principles — indeed, it means that what the IPCC has done is not science.

To conclude, the primary basis for global-warming alarmism is unfounded. The Met Office has been making false claims about the significance of climatic changes to Parliament—as well as to the government, the media, and others — claims which have seriously affected both policies and opinions. When questioned about those claims in Parliament, the Met Office did everything feasible to avoid telling the truth.

Harsh words, which could be applied with equal justice to pretty much the entire climate alarmism movement.

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