Published data were used to analyse the long-term annual temperature trends at 17 locations located in the UK, Ireland and the Faroe Islands. Similarities in the trends for individual stations enabled a comprehensive trend to be established for the whole region.
The data used were all from the website of KNMI (the Royal Netherlands Meteorological Institute). Only raw data were used (ie as originally recorded, without any adjustments). Data were only used from stations located in rural areas or in small towns so as to avoid the possible influence of urbanisation on the temperatures.
The periods of the data varied considerably (the earliest record, at Gordon Castle, commencing in 1781) with many of the records (as published by KNMI) ending in the 1960s. However, several other records were available commencing in the 1930s and extending up to the present. It is expected that additional data may be available at some of the stations used and at other stations, but these were not available on the KNMI website.
The plots shown below are of the annual mean temperatures at each of the 17 locations. On each plot a polynomial “best fit” trendline has been added. It should be noted that the trendlines near each extremity (ie near the start and end of the records) are quite sensitive to individual data points, whereas trendlines within the main body of the record are much more stable and reliable.
COMPARISON OF TRENDLINES
Annual Mean Temperature Trends
[ The basis of these trendlines can be seen from the analyses for the 17 individual stations – see next section ]
Annual Mean Temperature Residual Trends
[ The individual trend-lines have been adjusted by constant amounts to be approximately zero at around 1940 ]
ANNUAL MEAN TEMPERATURE TRENDS FOR INDIVIDUAL STATIONS
Valentia Observatory (Ireland) 1869-2015
Malin Head (Ireland) 1955-2016
Tiree (Scotland) 1931-2016
Stornoway (Scotland) 1931-2016
Thorshavn (Faroe Islands, Denmark) 1867-2016
Lerwick (Scotland) 1931-2016
Orkney (Scotland) 1827-1906
Gordon Castle (Scotland) 1781-1975
Braemar (Scotland) 1856-1969
Eskdalemuir (Scotland) 1931-2016
Dumfries (Scotland) 1871-1969
Stoneyhurst (England) 1848-1969
Valley (Wales) 1931-2016
Aberystwyth (Wales) 1889-1969
Ross-on-Wye (England) 1877-1975
Cockle Park (England) 1898-1968
Scarborough (England) 1872-1969
DISCUSSION AND COMMENTS
- The data analysed was limited to that which were available on the KNMI website. No suitable data were available for southern England.
- The annual mean temperature trend-lines for the 17 stations are remarkably similar.
- A well-defined cyclical pattern in the trend-line is apparent at most of the stations. Lows occurred in around 1900 and 1970, and Highs occurred in around 1940 and 2010, indicating a cyclical wavelength of about 70 years.
- The ~2010 peak was generally about 0.3-0.4 deg C higher that that in ~1940.
- The ~1970 trough was generally about 0.2 deg C higher than that in ~1900.
- The ~1970 trough was generally about 0.3-0.5 deg C less than the peak in ~1940.
- The consistency of the annual mean temperature trend-line at the 17 widely separated stations provides support for the good quality of the data and the conclusions drawn from the analysis.
- The well-defined cyclical pattern of the trendlines over such a wide area raises the question (un-answered by me) of the causes of this pattern.
- There is no evidence of alarmingly increasing temperatures in recent years. Conversely, there is strong evidence that a peak in the temperature cycle was reached in about 2010 and a decrease in the annual mean temperature of around 0.3-0.4 deg C could be anticipated to occur in the next 20-30 years.
This article was written by Brian Gunter of Narooma, NSW. In his previous life Brian was an engineering hydrologist involved over many years in the analysis of rainfall and river flow data for the planning of water resources projects in Australia, Asia and Africa. In recent years he has been one of the Marine Rescue NSW (previously Royal Volunteer Coastal Patrol) volunteer weather observers who operate the Narooma station for the Bureau of Meteorology.