In these next two posts I will give detailed plots of EWP versus CET for all months and seasons, and for the fiscal year from July to June, consequently updating details to October 2015, a month whose warmth shows Australian greenhouse gas emissions to be taking even firmer control of the climate. I will do them from July to June rather than by the calendar year, since owing to the greater variance in temperature during the northern hemisphere winter the problem of unusually cold or warm seasons being divided between two years is thereby minimised.
I originally intended one post, but will do the first half of the fiscal year in this post and then do January to June and a full fiscal year EWP versus CET graph later.
Graphs are done at intervals of 0.25˚C for the hotter half of the year from April to September and 0.5˚C for the cooler half from October to March to deal with larger mean temperature variance.
To clearly distinguish natural variability I will colour in a dark red all data points beyond 1974 when it became clear man-made greenhouse pollution was controlling the climate, a trend that intensified after the botched Kyōtō Protocol – whose absolutely first priority should have been an absolute and uncompromising zero-emissions target for Australia (both the most infertile and oldest continent, a feature that ought to demand exceedingly low per capita emissions, and the worst per-capita polluter) before any reductions in Europe, East Asia or the Americas were contemplated – untenably allowed the worst polluter the most lenient increase!
As we can see from this scatter plot, in July there is a general trend for drier months to be hotter-than-average. The effects of anthropogenic greenhouse pollution upon these trends is not large, since the red diamonds follow a similar type of pattern to the white ones, only the lower part (very cool Julys) is largely or completely absent.
The major outliers are the “hot-wet” Julys of 1779, 1828 and 1834, and the “cool-dry” Julys of 1913 (EWP 32.6 millimetres; CET 14.6˚C) and 1919 (EWP 57.9 millimetres; CET 13.9˚C). July 1919 was extremely dry in Northern Ireland – it is among the top twenty driest months there since 1910 – and clearly possessed a very striking block over Iceland. This Iceland block drew Arctic air over the UK, which was cooler than normal, but produced conditions settled enough for the UK to be unusually dry except in the east which was on the western side of a low pressure anomaly and most exposed to Arctic air:
The notoriously cold and sunless August 1912 is an outlier at the opposite end – it was certainly duller than February 1891, 1907, 1949 or 2008, and possibly duller than Februaries 1887 and 1895 – whilst the anthropogenic August 2004 is a “hot-wet” outlier, as is the extremely hot and thundery August 1997, which actually had a strong pre-anthropogenic parallel in July 1808, a month well-known by historians for its violent thunderstorms and large hail.
If anything there are fewer outliers that for the individual summer months, with no real “hot-wet” outlier since Australian greenhouse emissions seized control of the global climate. The main outliers are the “cool-dry” summers of 1972 (EWP 160.3 millimetres; CET 14.19˚C), the above-mentioned 1913 (EWP 114.4 millimetres; CET 14.70˚C) and 1864 (EWP 118.1 millimetres; CET 14.44˚C). 1913 was notable for the worst Sahel drought between 1870 and 1970, and no doubt the midlatitude westerlies were pushed south allowing lower-than-normal pressure over Europe and a persistent block over the north Atlantic.
|Temperature anomaly relative to virgin mean for northern summer of 1913. Note that the hot anomaly over West Africa reflects the worst drought (weakest monsoon) over that region during the base period.|
|US precipitation plus US and global temperature (GISS and NOAA) anomalies for February and September 1986. Note the similar cold across Western Europe and the extreme wet over the contiguous US|
It might be thought potentially possible in this transitional month that the red diamonds (largely controlled by man-made global warming) would follow a different pattern from the white diamonds largely controlled by natural climatic variability. This does not really seem to be the case on first glance, and even on a brief statistical examination I did not find anything to suggest that there had been a major change since 1974 in either Spearman’s ρ or Pearson’s r.
A striking feature is that the “cold-wet” outlier November 1910 was very sunny – possibly the sunniest of the century over the UK with 93 hours over Durham – yet the “warm-dry” outlier 1945 was distinctly dull with only 42 hours of sunshine over England and Wales (virgin mean around 60 hours). This apparent contradiction is not actually even rare, as we will see when discussing December.
Autumn:red diamonds near the top of the graph, as it is in this season where the influence of Australian mineral and road pollution is most apparent.
In addition to the hot autumns of 2011, 2006 and 2014, the record wet autumn of 2000 and the record dry autumn of 1978 are also anthropogenic outliers, whilst the record cool autumn 1786 is a natural outlier nearly equalled in 1740 and 1676.
The “warm-dry” outliers are:
- 1842 (EWP 50.9 millimetres; CET 7.2˚C)
- 1843 (EWP 18.2 millimetres; CET 7.4˚C)
- 1857 (EWP 31.0 millimetres; CET 7.3˚C)
- across the UK as a whole, these last two Decembers may in fact have been warmer than 1934 or 1974, since data suggest Scotland was much more exceptionally warm than central England
- 1953 (EWP 34.5 millimetres; CET 6.9˚C)
- 1971 (EWP 37.6 millimetres; CET 6.6˚C)
- 1988 (EWP 45.7 millimetres; CET 7.5˚C)
The “cold-wet outliers” are:
- 1874 (EWP 96.6 millimetres; CET -0.2˚C)
- 1886 (EWP 145.2 millimetres; CET 1.9˚C)
- 1981 (EWP 93.3 millimetes; CET 0.3˚C)
The reason such a cold, snowy month was at the same time so abnormally sunny is actually relatively easy to understand: that the disturbed nature of the atmosphere eliminated anticyclonic gloom and allowed the sky to complete clear even during short fine spells. This is quite unlike December 1953 or 1971 or 1988, where stable air and lack of wind meant low cloud never dissipated.
Even December 1981 was no gloomier than the average, whilst very limited reports on 1874 are uncertain. However, the snow-drenched but bright December 1886 is no isolated case: November 1910 (noted above) and January 1959 (second part) were similarly snowy yet exceptionally sunny, and many other cold months were also much sunnier than usual.