What is a heatwave?
Good question. Everybody thinks they know what a heatwave is – long, languid days in the sun, sea swimming, lying out on burnt grass and queuing for ice-cream vans. Met Éireann, though, has a specific definition of a heatwave for Ireland – it is five consecutive days where the shaded air temperature is more than 25 degrees. By that criteria, the present fine weather matches the definition of a heatwave.
Didn’t we have a heatwave last month too?
The period between July 17th and 19th were intensely hot in many parts of the country. On July 18th the temperature peaked at 33 degrees in Dublin, the second hottest temperature ever recorded in Ireland. The highest temperature ever in Ireland of 33.3 degrees recorded at Kilkenny on June 26th, 1887, is now a matter of dispute among climatologists, some of whom state that the reading is not consistent with other temperatures recorded in Ireland that day.
In any case, the temperatures in July did not constitute a heatwave as the 25 degrees-plus temperatures only lasted three days in most places. The current hot spell constitutes a heatwave as it began on Tuesday and is likely to last until Sunday at the earliest. So far there have been 30 degrees-plus temperatures recorded in the southeast and Saturday’s forecast is for 31 degrees.
[ Ireland’s highest ever August temperature of 31.7 degrees recorded in Co CarlowOpens in new window ]
What is causing the current heatwave?
The heatwave is being caused by high pressure which is centred around Denmark and is drawing up warm continental air from mainland Europe. The high-pressure area over us now means there is little in the way of wind to ameliorate the high temperatures. Europe is experiencing record-breaking temperatures in France and Spain. So is the United Kingdom. Fortunately for farmers, gardeners and Irish Water, it looks like the high pressure will drift away on Monday, bringing with it much-needed rain.
Is this all part of climate change?
This is the critical question. Ireland has had some long periods of hot, dry weather in the past. The summers of 1976 and 1995 were particularly hot. There were five days at the end of July 1976 where the temperature breached 30 degrees in Ireland. Similarly, the summer of 1995 was the warmest of all time. Kilkenny had a total of 27 days with temperatures in excess of 25 degrees. It was also the driest summer on record. Then few were talking about climate change. The summers of 1976 and 1995 were expected as part of the natural variability, just as the summers of 1985 and 2007 saw particularly poor weather. However, there is no denying the hot summer in Europe is exceptional this year. For the first time it has really brought home to the public the potentially horrific impacts of climate change.
There have been record temperatures of 41 degrees in England, a temperature few meteorologists thought would ever be experienced there. Satellite photographs show the south and midlands of England burnt brown with the prolonged drought.
France, Spain, Italy, Greece and Croatia have been battling wildfires for days or even weeks. A paper published in June in the Environmental Research: Climate journal said the impact of climate change was making all weather events more extreme. Hence, the unprecedented temperatures and drought experienced this summer in Europe.
Met Éireann forecaster Conall Ruth concurs with this view. He said hot spells of weather have always been with us, but they will become more frequent and intense as a result of climate change. “We can’t say specifically that this heatwave is being caused by climate change. However, we are seeing these sorts of episodes more frequently now.”
