Published data were used to analyse the long-term annual temperature trends at six locations located in South America. Stations selected were located in French Guiana, Brazil, Argentina and Chile.
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 mainly 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 used ranged from 51 years to 117 years of complete annual data. The earliest record, at Punta Arenas, commenced in 1888.
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 the trend-lines around 1970.
ANNUAL MEAN TEMPERATURE TRENDS FOR INDIVIDUAL STATIONS
Cayenne (French Guiana ) 1994-2015
Sao Gabriel da Cachaeira (Brazil) 1931-2014
Quixeramobin (Brazil) 1896-2014
La Quiaca (Argentina) 1911-2015
Pilar Observatory (Argentina) 1931-2015
Punta Arenas (Chile) 1888-2015
DISCUSSION AND COMMENTS
- The data analysed was limited to that which were available on the KNMI website.
- The annual mean temperature trend-lines for six stations showed cyclical, but different, patterns.
- Apart from Punta Arenas, the other stations all had large periods of missing data that made the assessment of trends difficult.
- Punta Arenas was an exception with a Low around 1980 and Highs around 1930 and 2010.
- At Punta Arenas the 1930 and 2010 temperature trends were respectively about 0.8 deg C and 0.4 deg C higher than in 1980.
- At the other stations the increase in temperature from ~1980 to ~2010 was generally 0.3-1.0 deg C.
- Prior to ~1980 the temperature trends were variable, with the temperature in ~1940 being generally between 0.5 deg C below to 0.4 deg C above that in ~1980.
- The trend-lines for the six stations are cyclical but variable.
- Incomplete data at five of the stations made trend assessment difficult.
- Most stations had a Low or plateau around 1970-1980.
- Punta Arenas was the only good record, having a cyclical trend-line but with a Low around 1980 and Highs around 1930 and 2010.
- The increase in temperature from ~1980 to ~2010 was generally 0.3-1.0 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.