A NEW STUDY raises questions about the highest temperature recorded in Ireland.

A preprint of the research garnered attention last year but the final version has now been peer-reviewed and published in full this week.
33.3C was recorded at Kilkenny Castle in June 1887 and remains unbeaten 135 years later.

The highest temperature since was 33.1C in Dublin’s Phoenix Park on 18 July last year.

This makes Ireland as the only country in Europe with a record temperature set in the 19th century.

A team of Masters students led by Katherine Dooley at Maynooth University have examined the record and found reason to doubt its veracity.

Highest daily maximum temperature records (at the time of the study's publication) of several NW European countries surrounding Ireland.

The study found that information relating to the 1887 record is missing or unknown, such as who made the recording, and where the recording was made on the grounds of Kilkenny. Some limited data is available: the type of thermometer used and the fact that it was housed in a Stevenson screen.

The team then looked to use similar methods employed by the World Meteorological Organisation (WMO) in assessing other historic records, as was used when examining the debunked 1922 hottest world temperature.

The team compared the temperature recorded on that day with temperature recorded at other stations that existed at the time, and also with temperatures recorded at a modern weather station at Greenshill in Kilkenny, close to the site of Kilkenny Castle.

Professor at Maynooth University and an author of the report, Peter Thorne told The Journal:

“What you find is that in every compass direction [...] that value in 1887 is either right on the edge of the distribution of modern-day differences, or entirely outside, particularly in the case of Phoenix Park.

“The difference in 1887 between Kilkenny Castle and Phoenix Park is larger than any value of difference in the modern era between Kilkenny Greenshill and Phoenix Park that has ever been obtained.

A graph from the study showing how much of an outliner the Kilkenny record was compared to other stations in 1887

“The final piece of evidence was using things that we call reanalysis which are effectively weather forecasts run retrospectively. There’s one type that uses just surface pressure and sea surface temperature and we could use that to look at the circulation.

Although it was consistent with warm conditions, it was not consistent with the pattern of temperatures that are not implied to be present on that day by that 1887 value on a physical basis.

Thorne said it is also unlikely that Kilkenny was significantly warmer than all surrounding areas:

“Temperature gradients tend to be low in summer and in daytime. There’s a diurnal cycle in wind so you get more mixing in the daytime than you do at night, particularly in the summer.

“So those kinds of temperature gradients may well be attainable in nighttime minima temperatures, particularly in winter, but are highly unlikely to occur in daytime maximum temperatures, particularly in summer.

The study notes that it is ultimately the responsibility of Met Éireann to interrogate the findings and determine whether a decision should be made to alter the 1887 record.

“We need to constantly look – and we do as the climate science community – at and reassess our understanding of historical measurements,” Thorne said.

“And that’s both extreme temperatures or extremes of climate, but also long-term changes in climate. So we’re constantly looking to improve our understanding of these measurements. No measurement is perfect.”

Thorne added that any change to the record will likely be a moot point within a decade, as the increasing impact of climate change is likely to see the 33.3C record matched or exceeded, with a temperature of 35C or 36C possible under the right weather conditions.

The study concludes that the highest verifiable temperature in Ireland was recorded in Boora, Co Offaly, in 1976, when 32.5 C was recorded.

This was before 33.1C was reached in the Phoenix Park in July last year, which is still undergoing verification, but will likely be confirmed as surpassing the 1976 record.

In a statement, Met Éireann said many other stations reported warm temperatures on that same day in 1887.

“The thermometer at Kilkenny Castle was housed to acceptable standards, inspected regularly, and was certified as accurate, therefore the observation is considered to be accurate and reliable,” the statement continued.

Met Éireann is the repository for climate data dating back to the mid to late 1800s. Data prior to the mid-1900s is still mainly on paper. Data rescue projects are ongoing to digitise this data. As more historical observations and new scientific research become available, all national records, indeed all climate observations are reviewed.  When as many as possible of the twenty-one stations mentioned above are rescued and quality controlled, we will reassess the Kilkenny Castle record.