Analysis: Long-term maximum and minimum air temperature series in Ireland show significant increasing trends

Ireland has a great heritage of instrumental meteorological observations dating back to the 17th century. The oldest known instrumental record includes daily barometer observations and weather remarks taken in Dublin in the period from January to April 1676, which have been published in the Philosophical Transactions of the Royal Society of London.

The interest in meteorological observations by cultural and scientific societies and educated individuals in Ireland emerged in the 17th and 18th centuries and flourished mainly up to the 19th century. Institutions, societies and amateur meteorological observers contributed to the temporal and geographical extension of instrumental records prior to the establishment of the Meteorological Office and Met Éireann, the latter in 1936.

The Royal Irish Academy, Royal Cork Institution and the Royal Dublin Society registered valuable historical meteorological observations. For instance, the Royal Irish Academy established a network of stations, including light-houses and coast-guard stations, that followed similar observational practices and instrumentation across the Island in the years 1850 and 1851, although these are short-term series.

Rainfall records from Blackrock, Co Cork in August 1881 Source: National Meteorological Library and Archive – Met Office, UK

Observers such as physicians, instrument makers, reverends, land owners, clerks, coast-guards, light-keepers, Royal Engineers at the Ordnance Survey, Army Medical Department, astronomers at observatories (Armagh, Birr, Dunsink, Markree) and professors at Queens College Belfast, Royal College of Surgeons in Ireland, Trinity College Dublin, University College Cork and University of Galway contributed to registering indispensable instrumental meteorological observations. An inventory of historical meteorological observations has identified 750 collections of documentary and instrumental records registered prior to the 20th century for distinct locations across the Island of Ireland.

Long-term historical meteorological observations are important to better understand past climate variability and assess the intensity, frequency, duration and distribution of extreme weather events. Moreover, daily and hourly meteorological observations are paramount to better assessing past and rare extreme weather events.

The analysis of long-term instrumental series is crucial to examining modern climate warming within a historical context. The long-term assessment and characterisation of extremes, namely of rare extremes, is important to support climate action, mitigation and adaptation policies, reduce vulnerability, enhance resilience, and mitigate the impact of future events in the context of changing climate.

Weather observations at Blacksod, Co Mayo in 1925 Photo: National Meteorological Library and Archive – Met Office, UK

For example, long-term daily maximum and minimum air temperature observations recorded in Ireland allowed for the first time the assessment of air temperature trends and daily extreme air temperature indices recommended by the Expert Team on Climate Change Detection and Indices (ETCCDI) based on quality-controlled and homogenised data dating back to 1885. These extreme air temperature indices have been widely used to assess changes in the frequency, duration and intensity of daily climate extremes of temperature ranging from the country to the global scale.

Significant increasing trends were assessed in the seasonal and annual maximum and minimum air temperature series in Ireland, with greater increases in the spring and autumn seasons in the period from 1885 to 2018. In the same period, significant increasing trends were determined in the warm nights (+7.5 nights), warm days (+6.8 days), warm spell duration index (+3.9 days), coldest night (+2.7 °C), coldest day (+1.5 °C) and growing season length (+22 days).

In contrast, in the same period, significant decreasing trends were identified in the frost days (−13.7 days), cold days (−9.3 days), cold nights (−7 nights), cold spell duration index (−6.9 days) and diurnal air temperature range (−0.1 °C) in Ireland. The results follow global patterns presented in the Sixth Assessment Report of the Intergovernmental Panel on Climate Change.

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From RTÉ Brainstorm, Conor Murphy, Conor Sweeney and Paul Dunlop look at how climate modelling works and what past data about our weather can tell us about what comes next

Despite the rich heritage of meteorological observations and data rescue efforts, numerous observations remain as paper data sources across multiple archives or online newspaper archives, which must be digitised in a computer-readable format and quality-controlled to fill important gaps in climate research. Additionally, metadata (information about data) on station surroundings, observation practices and instruments are crucial to examining the quality of historical meteorological records.

Climate data rescue projects consist of digitising observations from a scanned source into a computer-readable format, such as Excel templates. These projects are crucial to communicating climate science as part of outreach activities.

Historical meteorological observations have been rescued by secondary school students through student-scientist partnerships under service-learning, university students and as part of citizen science. Secondary school students have been engaged in climate data rescue by being hosted and trained at university and by receiving training at school. Further work should rescue, quality-control and homogenise the data available in paper data sources to fill key gaps in climate research.

Please contact the author if you know of any non-catalogued handwritten historical meteorological records or weather diaries held in private collections.

The views expressed here are those of the author and do not represent or reflect the views of RTÉ