Published data were used to analyse the long-term annual temperature trends at nine locations located in Alaska State, USA. 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 were all over at least a century (the earliest record, at Sitka, commencing in 1828).
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 around 1940 ]
ANNUAL MEAN TEMPERATURE TRENDS FOR INDIVIDUAL STATIONS
Barrow (Alaska, USA) 1901-2015
Nome (Alaska, USA) 1906-2015
Fairbanks (Alaska, USA) 1929-2015
Talkeetna (Alaska, USA) 1918-2015
Homer (Alaska, USA) 1932-2015
Yakutat (Alaska, USA) 1917-2015
Juneau (Alaska, USA) 1881-2004
Sitka (Alaska, USA) 1823-2000
Kodiak (Alaska, USA) 1869-2000
DISCUSSION AND COMMENTS
- The data analysed was limited to that which were available on the KNMI website.
- The annual mean temperature trend-lines for seven of the nine stations are remarkably similar with the exception of Barrow and Juneau.
- A well-defined cyclical pattern in the trend-line is apparent at seven of the stations. A Low occurred in around 1960, and Highs occurred in around 1930 (but varied between 1910 and 1940) and 2010, indicating a cyclical wavelength of about 80 years.
- The ~2010 peak was generally about 0.2-1.2 deg C higher that that in ~1930.
- The ~1970 trough was generally about 0.3-1.0 deg C less than the peak in ~1930.
- Juneau did not show any trough around 1960.
- Barrow shows an increase in temperature trend exceeding 2 deg C between 1940 and 2010. However, the temperature trend at Barrow has been virtually constant for the past decade.
- The consistency of the annual mean temperature trend-lines at seven of the nine widely separated stations provides support for the good quality of the data and the conclusions drawn from the analysis. Barrow and Juneau are outlier records (the reasons are unknown).
- There is no evidence of alarmingly increasing temperatures in recent years (except, perhaps, at the outlier record at Barrow). 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 0.5 deg C could be anticipated to occur in the next 30-40 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.