Guest post by Tony Brown
This short paper is a preliminary examination of BEST data to 1753, as compared to the Central England Temperature Record (CET) to 1660 (instrumental record) and 1538 (Extended by Tony Brown using thousands of contemporary observations)
This extension to 1538 was a central part of my article ‘The Long Slow Thaw,’ which also examined historic temperature reconstructions by Dr Michael Mann and Hubert Lamb
In the article, warming from the start of the CET instrumental record in 1660 to the present day was noted, albeit with numerous advances and reverses.
The extended CET record coincides well with a 2000 year reconstruction by Craig Loehle here;
And one by M. V. SHABALOVA and A. F. V. VAN ENGELEN : Evaluation of a reconstruction of winter and summer temperatures in the Low Countries, ad 764–1998
According to studies made by a number of climate scientists, CET is a reasonable proxy for Northern Hemisphere -and to some extent global temperatures- as documented in ‘The Long Slow Thaw’. However, as Hubert Lamb observed, it can ‘show us the tendency but not the precision’. In that light there are a number of comments that can be made about the Combined CET/BEST graph which are shown above in two versions that, viewed together, provide the opportunity to follow the ups and down of the ever changing climate over the 350 years of instrumental records.
(Note; The BEST extension to 1538 and the extension to both trend lines after 2012 in the first graphic are merely a graphing feature.)
There are a complex set of important UHI corrections applied to CET and described by the Met office as follows.
“The urbanisation corrections to the CET series have been applied since 1974. Initially they were just 0.1 degree C, in certain months, then gradually for more months of the year; from about 1995 onwards some of the corrections increased to 0.2 deg C, and by about 2002 all the corrections were 0.2 deg C.
The above applies to Mean CET. The urban heat island effect is much more noticeable for minimum temperatures than for maximum, so for the Minimum CET series the corrections are double those for Mean Temperature, whereas for Maximum Temperature it was deemed in fact that no correction was required.”
That the Met Office correct for urbanisation is interesting in itself, whether it is sufficient is also a matter of debate, but is outside the current scope of the current paper. BEST do not correct for UHI, in fact they make some mention of it having a cooling effect.
The crossover point of BEST and CET around 1976 –when BEST starts to rise steeply- may or may not therefore reflect that one record allows something for uhi whilst the other doesn’t.
CET has been in steep decline since around 2000.
BEST has been broadly level in recent years, which does not reflect the reasonable historic correlation between the ‘tendency’ of the two graphs as can be seen by following the trend lines since the start dates, albeit those of BEST seem at times to be exaggerated, perhaps reflecting Britain’s temperate climate.
The cold BEST period around 1750-1760 possibly reflects the very small number of stations used in their reconstruction-all in the Northern Hemisphere-which are not necessarily as representative of the global climate as CET has been found to be. Also, most of them were part of the Mannheim Palatine-a network of stations that predated GISS by 200 years. Each of these older stations have been very thoroughly scrutinised and their temperature record often adjusted downwards under the EU funded ‘Improve’ programme, as it was generally felt there was a warm bias.
The BEST trend line from 1753 to the present day is somewhat exaggerated through not being able to reflect the very warm period centred round 1730 which would provide a better balance than starting the record in a trough. The CET warming period from 1690 to 1730 (un-paralleled even in the modern record ) is well documented by such as Hubert Lamb and was noted here in the 2000 book ‘History and climate-memories of the future?’ This chapter from Phil Jones-page 61;
‘All five series show long term warming from either the late 18th or early 19th centuries. Recent years are only marginally the warmest of the entire series because of the warmth of the 1730′s (particularly in Western Europe) and the 1820′s (Northern Europe) The five series are CET, De Bilt, Berlin, Uppsala, Stockholm.’
That the start of the temperature rise noted in ‘The Long Slow Thaw’ precedes the start date of GISS and Hadley by many centuries is illustrated by Tony Brown (CET extended), Craig Loehle (revised reconstruction) M. V. SHABALOVA and A. F. V. VAN ENGELEN, and BEST. In this context such records as Hadley, GISS, and even BEST itself, can be seen as merely plugging into the long established warming trend at various points along the way, and do not mark the start of it. There is no sign in observational records, or in many well regarded scientific reconstructions, of the 900 year long sequence of gently falling temperatures as noted by Michael Mann in the ‘hockey stick’ handle, nor an ‘uptick that is any more notable than many periods in the past.
That there was a gradual warming of winter temperatures-the severity of which had substantially reduced the overall mean annual temperature during much of the earlier historic record- was noted by Reginald Jeffery in his book ‘Was it Wet or was it fine,’ written in 1898.
“By 1708 the middle aged would say where are our old winters?”