Published data were used to analyse the long-term annual temperature trends at nine locations located in Greenland, Iceland and Jan Mayen (Norway). Five stations were in Greenland, three in Iceland and one on Jan Mayen. 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 ranged from 48 years to 1158 years(the earliest record, at Stykkisholmur, commencing in 1846).
The plots shown below are of the annual mean temperatures at each of the nine 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 nine 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 trend peaks around 1920-1950 ]
ANNUAL MEAN TEMPERATURE TRENDS FOR INDIVIDUAL STATIONS
Engesminde (Greenland) 1949-2015
Nuuk (Gothab) (Greenland) 1866-2015
Prins Christianssund (Greenland) 1949-2015
Angmagssalik (Greenland) 1895-2015
Danmarkshavn (Greenland) 1951-2015
Stykkisholmur (Iceland) 1846-2015
Vestmannaeyjar (Iceland) 1884-2015
Akureyri (Iceland) 1882-2015
Jan Mayen (Norway) 1921-2015
DISCUSSION AND COMMENTS
- The data analysed was limited to that which were available on the KNMI website.
- The annual mean temperature trend-lines for the nine stations are remarkably similar.
- A well-defined cyclical pattern in the trend-line is apparent at all of the stations. A Low occurred in around 1980-1990, and Highs occurred in around 1940-1950 and around 2010, indicating a cyclical wavelength of about 70 years.
- Due to incomplete data during the past decade it is difficult at fice stations to be definite about a trend peak around 2010.
- The ~2010 “peak” was generally about 0.2-1.0 deg C higher that that in ~1940.
- The ~1980 trough was generally about 0.7-1.5 deg C less than the peak in ~1940.
- The consistency of the annual mean temperature trend-lines of the nine widely separated stations provides support for the good quality of the data and the conclusions drawn from the analysis.
- There is evidence of significant temperature rises in the past 20 years, but is is unclear (due to badly broken records) if a trend peak occurs around 2010.
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.