IRELAND CAN EXPECT more intense storms and wetter winters as global temperatures rise due to climate change, according to a meteorologist.

Overall, as greenhouse gas emissions push up the temperature of the planet, Ireland is gradually seeing hotter weather on average in all seasons, with winters likely to become warmer and wetter if the climate crisis is not mitigated.

A recent report on the latest climate science from the Intergovernmental Panel on Climate Change (IPCC) said that for Europe, rising global temperatures mean that cold spells and frost days will decrease, the intensity of hot weather extremes will increase, and sea levels (except in the Baltic Sea) will rise.

Met Éireann’s monthly statement for November 2021 recorded that all mean air temperatures were above their long-term average and nearly all sunshine measurements were above average too, while rainfall was below average almost everywhere.

Last year, all mean air temperatures were also above their long-term average in November – though dipped below average in most places in December – and rainfall for both months was above average.

An isolated patch of warm weather in winter is not necessarily related to climate change – for instance, Met Éireann’s head of forecasting Evelyn Cusack told The Journal last month that November’s “unseasonably warm” spell was due to a warm air mass that came from the south.

However, the national forecaster has observed a rise in temperatures during winter and throughout the year over recent decades, along with wetter winters and more intense storms, that can be linked to the changing global climate.

“We’ve seen that winter minimum temperatures are increasing and have been increasing over the past few decades,” said Pádraig Flattery, a Met Éireann meteorologist and climate researcher.

Higher winter temperatures lead to a reduction in the number of frost days and a shorter frost season, with projections suggesting that the number of frost days each year could decrease by up to 50%.

At the same time, while temperatures are gradually increasing, extreme cold events can still happen, like the big snowfall that hit the country in late 2010 and early 2011.
But it “all depends on how much warming we experience over the next few decades and the action we take now”, Flattery said.

“The less carbon we emit as a planet, the less warming we’ll experience and the less substantial impacts we’ll see here in Ireland, so it all depends on current action.”

“We know that Ireland is one degree warmer now than we used to be on average over all seasons. We know that the decade from 2006 to 2015 was the wettest on record and there’s a trend in the data set towards an increased winter rainfall, so we’re seeing wetter winters over the past few decades as well and a decrease in summer rainfall.

“We’re also seeing storm intensity increase. We know that a warmer atmosphere holds more moisture, so for every one degree the planet warms, we get 7% more moisture in the atmosphere, and this means the storms that do hit, hit harder, so we get more intense rainfall.”

In combination with a rise in sea levels, that means coastal flooding can be more extreme during winter storms.

Additionally, wetter winters can pose problems for the agriculture sector as changing weather patterns affecting crop yields.

“There’s also a theory that the melting of the Arctic is disrupting the jet stream – that air mass that travels around the latitude that Ireland’s at and brings us warm, moist air and keeps us at a temperate climate,” Flattery said.

“There’s early signs of the jet stream becoming more wavy rather than a constant stream, which can cause warm or cold air masses to linger over areas for longer,” he said.

“During the summer there was that extreme heatwave in North America and there’s a theory that that was due to the air mass hanging around for longer.

“We might see more of that in the future in Ireland, so a cold air mass could stay over Ireland for longer and lead to a more extreme cold event. It’s too early to say if that’s what’s happening or what will happen more with climate change, but evidence is starting to come in.”

How do we know if climate change caused a weather event?

Until recently, scientists were hesitant to declare whether a particular weather event was caused by climate change, but advances in research have created new ways of determining whether an event like a heatwave or storm would have happened or not in the absence of human-driven greenhouse gas emissions.

“This is a new field in climate science that’s called attribution science. It’s about attributing events to climate change or whether or not events would be possible under climate change or if climate change had an impact,” Flattery explained.

“We used to say, ‘oh, we can’t really tell if climate change has an impact’. But now the science has advanced to the point where we can run climate models and assess the weather events that would happen were we to not have released any greenhouse gases into the atmosphere,” he said.

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They can run a climate model to look at if fossil fuels were not burnt or greenhouse gases not produced, what would the weather patterns be like; and would a heatwave, a storm or a cold event be experienced in a world without any greenhouse gas emissions.

The World Weather Attribution initiative, a collaboration between climate scientists in the UK, Netherlands, France, the US, Switzerland, India and the Red Cross Climate Centre founded in 2014, is a leading group analysing weather events to determine whether or not – and how significantly – climate change plays a role.

It found the extreme heat that hit the northwest of the US and Canada this summer would have been “virtually impossible” without human-caused climate change, while the damaging flooding in Germany and Belgium that led to more than 200 deaths was made more likely and more intense by climate change.

In 2018, the WWA studied a summer heatwave in northern Europe that stretched from Scandinavian countries to southwest Ireland.

It estimated that the probability of that type of heat was more than two times higher than it would have been if human activities had not altered climate.

For a weather event like a heatwave, “you do need to do an analysis or study like that to be able to say, yes, climate change was a factor here”, Flattery said.

“But for things like storms, it’s basic physics to say that a warmer atmosphere carries more moisture and we know that will influence the power of storms, the intensity of storms, and the amount of rainfall that comes out of that storm, so extreme storms and the intensity of extreme storms can be linked to climate change on the basis of that physical fact,” he said.

“We don’t do much of it [attribution science] here in Ireland but we probably will end up doing more of it in the future.

“It’s hard to say for certain events in Ireland if that was due to climate change, but we can say generally that cold spells will decrease in Ireland, but that doesn’t mean we’re never going to have extreme snow again – we could have even more extreme snow because events become more intense.

“The main thing to highlight is that it all depends on the action that we take over the next few years how severe the impacts will be in the future,” he said.

These aren’t inevitable changes. While we have experienced changes already and we’ve committed ourselves to a certain level of warming, we don’t have to see the worst impacts of climate change.