Published data were used to analyse the long-term annual temperature trends at six locations located on islands in the Southern Ocean. 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). All of the data were located in rural areas or in small towns.
The periods of the data ranged from 45 years to 98 years of complete annual data. The earliest record, at Orcadas Station, commenced in 1903.
The plots shown below are of the annual mean temperatures at each of the six 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 six 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 troughs around 1960. ]
ANNUAL MEAN TEMPERATURE TRENDS FOR INDIVIDUAL STATIONS
Orcadas (South Okney, Argentina) 1903-2015
Grytviken (South Georgia, UK) 1905-2015
Marion Island (South Africa) 1948-2015
New Amsterdam Island (France) 1950-2015
Macquarie Island (Australia) 1948-2015
Campbell Island (New Zealand) 1941-2002
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 six stations are all cyclical and similar.
- Few records exit prior to aroud 1950 when there is an apparent Low or plateau in the temperature trend-line.
- At four stations a well-defined High occurred around 2000 with a plateau for the other two stations.
- The ~2000 High was generally about 0.5-1.0 deg C higher that that in ~1960.
- The trendlines for all six stations were all cyclical and similar with Lows or plateaus around 1960 and Highs or plateaus around 2000.
- The increase in temperature between ~1960 and ~2000 was generally 0.5-1.0 deg C.
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.