John Sweeney: 'We are leaving behind a terrible climate legacy - but we can still act'
Winter 2017/18 seemed to be going out with a whimper. Admittedly, the storm-naming count had reached Storm Georgina, but after the excitement of ex-hurricane Ophelia in late autumn of 2017, Irish climate had resumed normal winter service.
At least, that was, until February. It was apparent by then that an event occurring high up in the stratosphere, known as sudden stratospheric warming, was instrumental in developing a mountain of cold air over Siberia which was beginning a remorseless push westward towards Ireland.
Bitterly cold easterly winds set in, which by the end of the month were producing overnight temperatures of close to -6C, and in some cases daytime values that failed to get above -1C. The 'Beast from the East' distorted the normal jet-stream circulation over large parts of Europe and pushed Ireland's normal Atlantic feed of air well to the south.
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But another ingredient had to be added to the mix. It was in this disturbed circulation off the coast of Portugal that Storm Emma formed and tracked north to Ireland. Rich in oceanic water vapour, once this moist air mass was forced to climb over the cold Siberian air over Ireland it dumped its moisture as snowfall, the worst since the 'Big Snow' of 1982. Blizzard-like conditions and large snow drifts developed, and a red warning was issued by Met Éireann.
Schools, offices, buses and flights were suspended. More than 100,000 customers were without electricity, and 145 homeless people were accommodated in emergency beds as services of all kinds struggled to keep going, even with the help of 300 Army personnel and their vehicles. Who can forget the panic buying of bread and the demolition of a supermarket by a JCB as the country went into near- lockdown for several days? As the easterlies resumed, temperatures plummeted further, with days of sub-zero temperatures in early March.
After a brief respite, the drought and heat which was to characterise the 2018 summer began to be established. June saw a total rainfall of 3.8mm in the Phoenix Park, its lowest monthly total since 1941.
To emphasise how extreme this was, 16 times as much rain fell in the Donegal flood of August 2017 in only six hours.
At the same time, temperatures soared, reaching 32C at Shannon Airport, the highest for more than 70 years.
For a time, it looked like Ireland's all-time record of 33.3C set in 1887 might be reached as the anticyclone took up residence over Ireland.
The distress that the lack of pasture caused farmers would persist for a number of months. Southern Europe was experiencing temperatures over 46C and, even north of the Arctic Circle, values of 32C were being recorded. Forest fires with high fatalities occurred as Europe's hottest summer on record progressed.
These two major events of 2018 were linked by a common theme, namely the radical displacement of the jet stream.
For the spring freeze it was displaced far to the south, while for the summer it was north of the Arctic Circle.
It is these aberrations that allow extremes to develop and a feature of recent years in Ireland has been the growing number of extreme events, especially high rainfall days.
According to the World Meteorological Organisation, the severe heat of 2018 can be linked to climate change, essentially to the rapid warming of the polar regions. This is believed to weaken the strength of the jet stream and cause it to meander erratically. Extreme weather events of various types result.
Some researchers have estimated global warming has doubled the likelihood of heatwaves such as happened this year.
The kind of weather events we have experienced in Ireland cannot be classed as once-off occurrences, but rather symptomatic of where we are headed as the planet warms. If this is so, we face into a future where the high price of not tackling climate change will increasingly be apparent and we will leave a most unwelcome legacy to those that come after us.
John Sweeney is Emeritus Professor at the Irish Climate Analysis and Research Unit, Maynooth University