This post summarises my analyses of recorded annual mean temperature trends at 250 stations worldwide. The stations were all with long records (many over 100 years) and located in rural areas or small towns. The analysis used raw data (as recorded, without any adjustments) as published by KNMI (the Dutch Meteorological Institute) or BOM (the Australian Bureau of Meteorology). Polynomial curves of best fit were added to the plots.
There was a sparcity of suitable records in Central/South America and in Africa, whereas good records were often found to exist for isolated island locations and in the polar regions.
The following characteristics of the trendlines at the individual stations were assessed:
– the occurrence of a cyclical trendline pattern,
– the occurrence of a peak or plateau of the trendline in the period since about 2000,
– the occurrence of a trough in the trendline in the approximate period 1950-1990,
– the occurrence of a level or steadily decreasing trendline over the past century or more.
The assessments of each of these characteristics are somewhat subjective, so the resulting statistics have been rounded to the nearest 5%. In some cases there were insufficient data (for example, due to short, incomplete or missing data), so the sample sizes for each characteristic are not equal.
RESULTS OF THE ANALYSES
About 95% of stations had good records over a period of at least 70 years (used to identify cyclical and trough trendlines).
About 85% of stations had good records since about 2000.
About 75% of stations had a cyclical trendline.
About 80% of stations had a peak or plateau trendline in the period since about 2000.
About 50% of stations had a trendline with a defined trough during the approximate period 1950-1990.
About 20% of stations had a trendline which had no peak or plateau since about 2000.
About 10% of stations had a trendline over the past century or more which was either essentially level or steadily decreasing.
Examples of stations that show the following characteristics are:
– Prince Albert (Canada) – stations with cyclical trendlines with a peak or plateau since 2000 and a trough between about 1950 and 1990.
– Bodo (Norway) – stations with no peak or plateau in their trendlines since about 2000.
– Isla Juan Fernandez (Chile) – stations with essentially level or steadily decreasing trendlines over the past century or more.
Prince Albert (Canada) 1884-2015
[ The Prince Albert station is located in a small prairie town in Saskatchewan, Canada. There is a well-defined cyclical trend with peaks around 1930 and 2000 and a trough around 1970. ]
Bodo (Norway) 1868-2015
[ The Bodo station is located in a small coastal town in northern Norway . There is a cyclical trend with a peak around 1940 and a trough around 1980. Since about 1980 there has been a steady increase in the trendline without any indication of a peak having been reached. ]
Isla Juan Fernandez (Chile) 1901-2015
[ The Isla Juan Fernandez station is located on an island in the Pacific Ocean about 650 km off the South American coast. There is no cyclical trend with peaks, but a fairly steadily decreasing trendline since records commenced in 1901. ]
A cyclical trendline of annual mean temperatures was identified in about 75% of the 250 stations analysed.
Typically the cyclical trendlines had peaks in around 1920-1940 and 2000-2010, with troughs in around 1960-1980.
A peak or plateau in the trendline was identified in about 80% of the stations analysed.
Conversely, about 20% of the trendlines were increasing, with no peak, in the period since around 2000.
Trendlines that were decreasing or were essentially level over the past century were identified in about 10% of the stations analysed.
The analyses show that, worldwide, annual mean temperature trendlines are predominantly cyclical with cycle periods of around 80 years.
At the present time (2017) the annual mean temperatures at the vast majority (about 80%) are at ,or maybe even past, the peak of the natural cyclical trendline.
The increases in the annual mean temperature trendlines between about 1960 and 2000 are general of similar magnitude to those that occurred in about 1900-1940.
If the cyclical trendline continues, it would be expected that worldwide temperatures will stabilise, or perhaps decrease, in the coming years until the next trough in about 2014. This would be a repetition of the historical trendline between about 1930 and 1970.
Links to the analyses of the long-term temperature trends at all 250 stations analysed are presented within 27 smaller regional blog posts:
Please let me know what you think of my analyses. email@example.com
This article was written by Brian Gunter of Narooma, NSW, Australia. 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.