MANY PEOPLE DREAM of a white Christmas, but we may have to become used to a sodden Christmas instead due to climate change.
A white Christmas has always been a rare occurrence in Ireland and is becoming rarer still due to climate change, according to Met Éireann.
While there will be a brief cooler spell today, it won’t bring any snow as temperatures are not cold enough to bring any wintry precipitation.
Paul Moore is a climatologist at the State’s meteorological service and explained that a white Christmas is one where there is lying snow at 9am at one of the main primary stations.
The last time that happened was during the Big Freeze of 2010, and it’s happened nine times in all since 1964.
Back in 2010, the highest total of lying snow in Ireland on Christmas Day was recorded – 27 centimetres at Casement Aerodrome.
“But with climate change, cold extremes are becoming both less severe and less frequent,” Moore told The Journal.
“There are fewer cold nights and cold days on average, so with that, there’s going to be less chance of snow in general and of a white Christmas.”
The average December day now has a mean temperature of around seven degrees.
While Moore notes that December, January, and February are still the most likely months for Ireland to get snow, he adds that climate change means “one day events like a white Christmas become less common”.
Speaking to The Journal, environmental journalist John Gibbons recalled the Big Freeze of 2010.
He noted that while overall temperatures in Ireland are tracking the global average temperature rise, there can still be occasional and intense cold snaps.
“It was absolutely intense for around three weeks,” said Gibbons on the 2010 Big Freeze.
“The scientists looked at that event and it was considered to be due to increased waviness of the jet stream.”
Gibbons describes the jet stream as a “high-altitude, fast-moving air current that is pinned between the North Pole and the mid latitude”.
“This is a fast-moving zone, it’s called the jet stream because that’s where a jet aircraft literally flies in and that’s why it’s much faster to come back from America to Ireland than it is to go from Ireland to America, because the jet stream is traveling so quickly.”
Gibbons explained that the jet stream is the main controller of weather systems in the northern hemisphere, but that it is “becoming erratic”.
“Occasionally, it will wobble a huge blob of cold air over Europe that’s what happened in Ireland in 2010,” added Gibbons.
He also noted that this type of extreme cold, though rare, “is ironically one of the signatures of global warming, which is a destabilisation of the jet stream”.
While Gibbons said we will have fewer white Christmases on average in the future, he added that we will “still have occasional cold snaps, particularly ones related to the jet stream”.
Despite the possibility of a cold snap, Gibbons told The Journal that the “general climatic shift in Ireland is that we’re moving towards drier, warmer summers, and wetter, milder winters”.
“The amount of rainfall in Ireland in the last couple of decades has increased by 7%, it’s a huge change and one of the reasons we’re seeing more and more flooding events,” said Gibbons.
“With every additional degree of global warming, we get an extra 7% precipitation in the atmosphere.
“Assuming global warming continues on its current path, it’s going to get an awful lot wetter in Ireland.
“I think it’s far more likely that we’ll have sodden Christmases rather than white Christmases.”
However, there is what Gibbons refers to as a “joker in the pack”, which is the Atlantic meridional overturning circulation.
It’s an Atlantic current more commonly known as the AMOC.
“That’s the current that draws up warm, salty water from the Caribbean, and basically warms North-west Europe,” Gibbons told The Journal.
“That’s the reason we have the mild temperatures that we have in Ireland. At our latitude, we’re on the same as that of Newfoundland in Canada, which is frozen for seven or eight months of the year.
Gibbons warned that the AMOC has slowed down by about 15% in the last two to three decades.
A study published in Nature in July of this year had a “95% confidence range” that the collapse of the AMOC will occur between 2025 and 2095.
“In the event of an AMOC shutdown, we’re going to have a much colder climate in Ireland and across Northwestern Europe, which is kind of ironic that that would happen inside a global warming event,” said Gibbons.
“You’d have regional cooling set against a fast-warming globe.
“It that were to happen, it would mean not just white Christmases, but white Januarys and Februarys, probably white all the way out to May, starting in about September, in the event that we lost all or most of the heat energy from the AMOC.”
Gibbons added that the AMOC is the reason why a typical November’s day in Ireland is around 12 or 13 degrees, instead of two or three degrees.
“If one was looking for a white Christmas in the future, in an AMOC collapse scenario, we would have a climate similar to Northern Canada and that wouldn’t necessarily wouldn’t suit us, let’s just say.
“We’ve kind of evolved to our mild climate pretty well in agriculture and our transport system.
“Everything here in Ireland is built around this climate system, so it would be nice to hang on to this climate system if possible,” said Gibbons.
Gibbons added that the AMOC is a “very big system and it’s unlikely to simply switch off”, and that he doesn’t foresee it shutting off before 2050.
However, he noted that it is “beginning to break down and it’s definitely slowing and losing energy and there is a critical point at which it will stop”.
In that scenario, Gibbons told The Journal that “weather systems will turn upside down” and that “super” storms would develop which are “storms beyond anything that modern humans have experienced”.
“The consequences of the AMOC shutting down would be just unimaginable because this is the climatic system that we have evolved to work with.”
Meanwhile, Met Éireann climatologist Paul Moore told The Journal that “some research is saying that we may have started towards an AMOC collapse”.
However, he added that if the AMOC does collapse, “there won’t all of a sudden be snow every day in the winter”.
“It’s a gradual thing over 50 to 100 years where it’ll gradually get colder in the winter here due to the cooler temperatures that the collapse of AMOC would bring,” said Moore.
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