YESTERDAY, IRELAND RECORDED its hottest temperature in 135 years, with the Met Éireann measuring site at Phoenix Park recording a reading of 33.1°C at 3pm.
The temperature is second only to the record of 33.3°C measured in Kilkenny Castle on 26 June 1887.
However, one climatologist has cast doubt on the long-standing record, arguing that yesterday may in fact have been the hottest day ever reliably recorded in Ireland.
Peter Thorne, climatologist and professor at Maynooth University, has co-authored a paper entitled Reassessing Ireland’s Hottest Temperature Record, which is currently being peer reviewed and was resubmitted yesterday morning for what he hopes is the final revision.
The paper suggests that the recording in Kilkenny Castle in 1887 may be unreliable.
“My own personal take would be that [the Phoenix Park temperature] constitutes the hottest reliably observed temperature in the history of meteorological observation on the island of Ireland,” he told The Journal.
“That doesn’t mean it hasn’t been hotter way back in a time when we never observed, and of course it’s an observation at a place at a time, and we have not observed Ireland at a necessary density maybe in the past, and maybe even today. Almost certainly, somewhere was warmer than the Phoenix Park, we just didn’t happen to have a thermometer there.”
In 2020, Thorne assigned his Masters students at Maynooth’s Irish Climate Analysis and Research UnitS (ICARUS) to look at Ireland’s historical high temperature record and reassess how accurate it is
He said the study was inspired by various World Meteorological Organisation (WMO) assessments of new and historic heat records.
In 2013, the WMO reassigned the highest recorded temperature for the planet from an observation of 58°C made in north Africa in 1922 to a 56.7°C, recorded in California in 1913.
As part of the Irish study, one group of students spoke to Met Éireann about what is known about the 1887 temperature reading, while another group of students conducted a reanalysis, which involves running modern day weather forecast models retrospectively with the observations that were available at the time.
The first group found that the original time series record was not retained, so that only the observation of 33.3 degrees centigrade was recorded – but without the accompanying data which showed how it was measured.
“We know it was taken somewhere in the castle, and its grounds, but we have no idea where and we therefore have no idea whether it suffered from representativity errors. We also don’t know who the observer was and whether the ordinary observer took that observation or whether the ordinary observer, for example, was on holiday and the substitute observer was taking observations,” Thorne said.
There are just too many unknowns in there to really have confidence in that observation taken together with the fact that when compared to other stations around the island of Ireland on the same day, it looks a massive outlier.
When the temperature was taken in 1887, it was before the standardisation of meteorological instruments and methods of observation, which came later in the 20th century.
“It would have been mercury and glass thermometers, and it probably would have been a maximum and minimum thermometer. [The weather station] is something that would look like a meteorological shelter that we see today, but it would have been probably smaller because the large shelters were an innovation that came around in the First and Second World Wars,” Thorne explained.
“It would have been smaller and the smaller size of that would have left it more prone to solar heating effects during the day, and then coupled to that would have been [questions about whether] it well sited, was it near a wall of the castle that might heat during the day and expel heat. We know it wasn’t modern day instrumentation, and we know it wasn’t necessarily made with modern day standards.”
The reanalysis also compared the temperature recorded in Kilkenny to six other weather stations, including in Birr, Phoenix Park, Roches Point, and Sheffield in the UK.
These stations have nearly complete records through to today, many of which have been digitised, according to the study.
“We can look at the modern day differences between those and when we look at the date in 1887, the Kilkenny Castle difference is either entirely outside the distribution of expected daily occurrences or right in the extreme of that distribution,” Thorne said.
“So in every direction, north, south, east and west, Kilkenny’s difference in 1887 to those sites is a very, very extreme outlier, and there’s just no physical setup that could explain that difference.”
The group then examined what the actual record would be, and concluded that a site in Boora, Co Offaly, had the highest reliably recorded temperature since records began, at 32.5°C, which was attained on 29 June 1976.
That is, Thorne said, until yesterday. He added that the records are officially set by Met Éireann, and that it is up to them to decide if the Kilkenny record stands.
“I would hope that they would look objectively at the analysis that we have performed and undertake their own assessment of veracity of the Kilkenny Castle record. I think that the comparisons between Kilkenny Castle and the available network of surrounding stations on the island of Ireland is pretty firm, conclusive evidence in my view that that Kilkenny record is wrong,” he said.
“But ultimately that’s a call for Met Éireann to make, as we make very, very clear and continue to do so in the resubmitted draft. It is for Met Éireann to decide.”
He points out that the 2013 revocation of the world’s record hottest temperature by the WMO is “a far bigger deal than a national record standing or falling”.
“If [Met Éireann] are going to say ‘well, we can’t because it’s got precedent, it’s the record’, it’s a pretty weak argument given that the WMO decided to cast aside the world record value when they found it to be questionable for much the same reasons.”
What is not questionable, he said, is the reliability of the 33.1°C temperature recorded yesterday in Phoenix Park.
“It’s undertaken by Met Éireann in Phoenix Park using modern instrumentation in a well maintained site. I think we would have 100% confidence in today’s value given the way that Met Éireann maintain the instrumentation and the site,” he said.
“It would be as close as you can get to an unimpeachable value. Ask me where I’d put my money, I’d put my money on 33.1°C.”
Head of Forecasting at Met Éireann Evelyn Cusack has said that the 1887 Kilkenny Castle record is “sacred”.
Speaking on Newtalk’s The Hard Shoulder programme yesterday, she said: “Contrary to reports in the media, that is confirmed. That is a proper temperature.”
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