Friday, 1 April 2016

Before and after: temperature correlations before and with Australian greenhouse emissions – Part I

In two previous posts (here and here), I considered the relationship between England and Wales Precipitation (EWP) and Central England Temperature (CET) and showed that:
  1. the relationships in “summer” (April to September) and “winter” (November to February) are opposite in sign
    • in “summer” the relationship between EWP and CET is negative, whereas in “winter” it is positive
    • these differences are naturally due to the greater temperature variation of dry continental airflows producing low EWP values vis-à-vis moist maritime ones providing high EWP values
  2. despite a definite climatic impact through greenhouse emissions from Australia, South Africa and the Arab Gulf States, these relationships remain essentially the same as they were pre-1974 or even pre-1895
In this and the following post I will have a look at the relationship of winter CET with winter temperatures in various parts of the United States, with the aim of finding out whether a change in basic relationship has occurred between temperatures on a more global scale.
Ever since the discovery of the North Atlantic Oscillation in the middle nineteenth century, and especially since Frederick Löwe’s ‘The Temperature See-Saw between Western Greenland and Europe’, which celebrates its fiftieth anniversary this year, it has long been known that winter temperatures in the CET area, and as far east as the Ural Mountains, show a strong inverse correlation with those in western Greenland (but not necessarily eastern Greenland). It is important to recognise, as Löwe did, that winter temperatures in Greenland and other regions of the true Arctic (defined as those areas above the northern timberline) showed a major abrupt rise during the 1920s, as can be seen via the following graph:
Global virgin period northern winter temperatures before and after 1920. Note the large increase in northwest Greenland and other regions of the true Arctic and contrast with erratic changes elsewhere
We can see Löwe’s observations clearly for the very cold months over the UK in January and February 1895:
Note here that this figure was across western Greenland, as Löwe noted in his original article, much further above normals from 1881 to 1910 than this picture shows. Anomalies relative to 1881 to 1910 means reached during the first three months of 1895 as high as +6.9˚C or +12.4˚F in northwest Greenland. When we look at the next subzero UK or CET mean temperature in 1939/1940 we see the anticorrelation more clearly:
January to March 1947 was the first example of this anticorrelation to be widely publicised by the meteorological journals, owing to Jerome Namias’ Monthly Weather Review article ‘Characteristics of the General Circulation over the Northern Hemisphere during the Abnormal Winter 1946/47’ showing how abnormal was the easterly flow both at sea level and aloft during February and March:
1962/1963, though the third-coldest winter in the CET series, the coldest therein since 1739/1740, and the coldest over the UK since at least 1813/1814 (January 1814 had an estimated UK mean temperature of -3.4˚C or 25.9˚F, 1.4˚C or 2.52˚F colder than any month since) was less publicised at the time, but still demonstrates the same relationship observed in 1895, 1940 and 1947. Löwe shows that previously in 1846/1847, another cold winter in Europe was also very warm in western Greenland.
December 2010, despite the severe impact of Australian greenhouse emissions, remains a “classic” map over the high latitudes nonetheless:
We also naturally observe anticorrelation in mild UK winters that were very cold over western Greenland, though even if globally no warmer, such winters tend to see reduced energy demand due to warmth over more-populated areas. This is clear in the winter of 1883/1884, the coldest on record over western Greenland but among the ten warmest of the nineteenth century in CET – and more famous for record heavy rainfall in Los Angeles and San Diego, sometimes blamed on the previous August’s Krakatoa eruption:
The winter of 1897/1898, which began forty years of mild winters over the UK, is another conspicuous example:
More modern examples can be seen in the winters of 1921/1922, 1974/1975, 1988/1989 and 1992/1993. (I have used a 1921-1974 base period to show how unusual 1992/1993 was compared to the post-1920 mean, within which period it constitutes the coldest winter in the Greenlandic capital Nuuk). Despite the modest UK departure, the cold over Northeast Africa and warmth over Eastern Europe shows a clear positive NAO signal for this winter.
If we look at the above cold UK winter months, we might notice that there seems to be a pattern of cold weather in the southeast of North America and warm weather in the northwest, including Alaska. The warm winters do – to a smaller extent – seem to follow the reverse pattern of warm weather in the southeast and cold weather in the northwest and Alaska. To test this on a broader scale, I will take a representative selection of states and stations in the United States and see whether:
  1. these observed predictions do hold
    • I will measure this by means of the virgin (up to 1974) Spearman ρ Pearson r correlation coefficients between CET and the winter temperatures of each North American region
  2. following from the basic aim outlined at the start, testing whether these relationship still hold for the period influenced or completely controlled by Australian greenhouse emissions

Florida (Southeast Region)

For Florida, representing the southeastern United States, we see a very simple positive correlation based on both Spearman and Pearson coefficients (not significantly different) for both the virgin period and even the post-1997 period where the influence of largely Australian-made greenhouse pollution took a further step beyond what it was from 1974 to 1997. Indeed, for all three colours of dots there is a clear line of best fit.

Ohio Valley Region (WV, KY, TN, OH, IN, IL, MO)

For the Ohio Valley Region, north of Florida, the graph is essentially similar in shape (only with of course vastly cooler temperatures). Winter temperature clearly correlates positively with CET, and this correlation is not contradicted except by a few outliers such as 2013/2014 and 1898/1899.

Texas (South Central Region)

Here, unlike the more easterly regions of the United States, only a slight positive correlation exists, with the virgin Spearman and Pearson standard deviations only a third of those for Florida and the Ohio Valley region.

The thing to do here is to look closely at the light red and dark red diamonds and see whether they form a similar sort of graph to the white diamonds. Without detailed calculation, it appears that in fact they do. Looking closely at the graph of CET versus Texas winter temperatures certainly visualises a similar shape for the diamonds of all three colours, although the full-period Spearman and Pearson correlations are considerably higher than for the three climate periods (1896 to 1974, 1975 to 1997 and since 1998) taken separately. Most especially, there are no extreme outliers coloured light or dark red – which could theoretically occur if opposing influence of natural variability and man-made greenhouse emissions gave different results over Texas and the UK.

Maine (Northeast Region)

Maine, lying near the boundary between positive temperature correlations with NAO to the south and negative correlations to the north, shows a more consistent increase in winter temperatures than seen in the southern United States. As can be seen, the virgin Spearman and Pearson correlations with CET are near zero, but for the whole period a positive correlation is definitely detectable; however, the lack of diamonds in the bottom left is notable compared to the Ohio Valley. Like Texas, however, there are no outliers caused by differential response when global warming and natural variability oppose one another.

If we look at the dark red diamonds, it is clear that those at the top show a full spread re their CET value. The same is clearly true of the lighter red diamonds – the temperature in Maine in the cold UK winter of 1978/1979 and the very warm winter of 1974/1975 – nor does any pattern exist for the dark red diamonds. Thus, Maine, like the southeastern regions, does not contradict the thesis that no change in natural relationships of CET with temperatures elsewhere has been caused by Australian greenhouse emissions.


We can see that, from out studies relating CET winter temperature to winter temperatures in the eastern half of the United States that:
  1. owing to greenhouse gas emissions largely sourced from Australia, South Africa and the Arab Gulf States, temperatures have risen steadily since 1975 in both the UK and eastern North America
  2. before 1975 definite natural positive relationships existed between UK winter temperatures and winter temperatures in southeastern North America
  3. no significant relationship exists between UK winter temperatures and those in:
    1. south-central North America (Texas)
    2. east-central North America (Maine) 
  4. despite the marked increase in all regions’ temperatures, the relationships between them have not changed substantially under the influence of man-made greenhouse emissions largely sourced from a few mineral-rich desert states

No comments: