Doug Keenan has just pointed me to a very interesting parliamentary question and answer. As ever the protagonists are our old friends Lord Donoughue and Baroness Verma, and once again the subject is statistical models. I've inserted some clarification suggested by Doug in brackets. This has no bearing upon the answer.
To ask Her Majesty’s Government, further to the Written Answer by Baroness Verma on 25 May 2013 (WA 44–5) which stated a linear trend model with first-order autoregressive noise [is very unlikely to be an appropriate model] in representing the evolution of global annual average surface temperature anomalies, and in the light of the Working Group I Contribution to the Intergovernmental Panel on Climate Change Fifth Assessment Report which states that statistical analyses of climatic time series “have to assume some kind of model, or restricted class of models”, what models they rely upon for statistical analyses of global temperature series; and why they chose those models.[HL4497]
The Parliamentary Under-Secretary of State, Department of Energy and Climate Change (Baroness Verma) (Con): Her Majesty’s Government does not rely upon any specific statistical model for the statistical analysis of global temperature time series.
Global temperatures, along with many other aspects of the climate system, are analysed using physically-based mathematical models, rather than purely statistical models.
Read that again. The government no longer performs statistical analyses of the temperature records. They rely instead of comparisons of the temperature records to GCM outputs. Having admitted the inadequacy of the AR1 model normally used to make claims of significant changes in the temperature record, and having also agreed that an alternative model - suggested by Doug and under which these temperature changes can only be seen as natural variation - is much more likely to be correct, this approach seems to be the only one open to them.
Carbon dioxide is still a greenhouse gas of course, but it is startling to realise that the government has effectively abandoned the temperature records as evidence for global warming. Everything comes down to the climate models.