Valentia Monthly Temperatures

This post refers to my analysis of recorded monthly mean temperature trends at Valentia Observatory in south-western Ireland.  The station was established in 1869 on Valentia Island but was relocated to the mainland in 1892.  The analysis used raw data (as recorded, without any adjustments) as published by KNMI (the Dutch Meteorological Institute).   Polynomial curves of best fit were added to the plots.

The present Valentia station is near the town of Cathersiveen in County Kerry.  Records commenced in January 1869, having been relocated from nearby Valentia Island in 1892.

Over the 1869-2016 period (a period of 148 years) the years are 95% complete.

Valentia has a mild climate typical of coastal locations adjoining the northeastern Atlantic ocean.    Mean monthly temperatures vary from 7.1 degC (in February) to 15.2 degC (in August).  Extreme monthly mean temperatures recorded are 2.6 degC (in January 1963) to 18.0 degC (in August 1995).

Mean, Maximum and Minimum Monthly Temperatures


Plots are shown below for annual mean temperature and the monthly mean temperature for each of the 12 months.  A polynomial trendline was fitted to each graph.  A comparison of the monthy trendlines are also presented.   It should be noted that the trendlines (in red) can sometimes be misleading at either end of the series as the line is very dependent on the temperature values in individual years (this sensitivity does not occur away from the start and end of the series).


Annual Mean Temperatures


Monthly Mean Temperature Trendlines



























  • The plots all show cyclical monthly trendlines with peaks around 1930 and 2010 and troughs around 1900 and 1970, a cycle period of about 70-80 years.
  • The peak monthly trendlines around 1930 are generally of similar magnitude to those around 2010.
  • A peak or plateau in the trendline around 2010 is observed to occur in most months.
  • The average temperature trends since 1869 are about +0.25 degC/century (+0.5 degC/century for trend peaks and +0.3 degC/century for trend troughs).
  • There are no alarming increases in the temperature trendlines in recent decades.


Valentia is one of  257 stations, worldwide, for which I have analysed long-term temperature trends.   The analyses at 50 representative stations are summarised in the blog post:   world-50-temperatures



Please let me know what you think of my analyses.


The Author:

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 Australian Bureau of Meteorology.




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