To finish the survey this post will give an overall examination of the observed correlations for each month and for all months. The first step will be to graph the observed CET anomaly versus global temperature anomaly correlation coefficients between 1880 and 1974 for each of the twelve calendar months. They are arranged in fiscal year order in the graph to fit in with my previous research on CET – a choice made because temperature anomalies are larger in winter than in summer.
|Monthly Central England Temperature anomaly versus global temperature anomaly correlation coefficients, 1880 to 1974|
- There would be no difference in correlation for all months
- There would be a maximum in summer (when natural variance of CET and global temperature anomalies are smallest) and minimum in winter (when they are largest because air advection influences are greatest and most independent of greenhouse gas concentrations)
- There would be maximum in autumn (when CET has increased most consistently and the effect of retention of heat by greenhouse gases appears greatest) and minimum in late winter and early spring
A likely conclusions is that, for the summer months when natural variability is lowest, a sample size of ninety-five years is too small to give accurate correlations at the monthly level. When variability is lower at the local level, smaller changes in temperature can have more effect on the anomaly, especially upon its sign.
If this be so, then we can conclude that over an adequately long period, the correlations between CET and global mean temperature would trough in the winter months at around +0.09. What value they would take in months with negative EWP versus CET correlations (April to September) is less certain. The graph above shows +0.11 and +0.21 as the plausible limits, but what to expect is not certain. We cannot test any years before 1880 since I cannot gain access to compatible values of global temperature anomaly. Testing the post-1974 period is a possibility to expand the sample size, but I am too wary that global warming via greenhouse pollution out of Australia, the Gulf States and South Africa will have distorted the results vis-à-vis the relatively consistent climate of the 1880 to 1974 period.