Analysis: New research shows that Ireland's coldest winters are warming faster than our hottest summer heatwaves
By Dáire Healy and Andrew Parnell, UCD
Climate change is typically associated with warmer summers and increasing heatwaves and changes in cold winter temperatures receive far less attention. But new research suggests that this is where some of the fastest changes in Ireland are taking place.
Using historical winter temperature records from weather stations across Ireland between 1950 and 2022, we found a large reduction in extreme cold. The coldest winter days are becoming both less frequent and less severe.
The disappearing deep freeze
In the last seven decades, our research shows that the coldest winter temperatures in Ireland have been warming at a much faster rate than average winter temperatures. Surprisingly, these winter lows are warming faster than our summer heatwaves.
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To contextualise this change, we can look at the most extreme cold on record. The lowest temperature ever observed in Ireland was -19.4°C (Omagh, Co. Tyrone, January 1881). Since 1950, the likelihood of any weather station reaching this level has fallen by around a factor of 100. An event that was once very rare but plausible has become extremely unlikely under current conditions.
The changes are not uniform across our island. Inland areas, which experience larger winter temperature swings, show the greatest warming of extreme cold. Coastal regions, moderated by the surrounding seas, show smaller changes, but the same overall trend.
On average, Irish winter temperatures increased by about 0.9°C over the study period, but the "coldest of the cold" days have warmed considerably more than that.
Why severe cold still occurs
You might remember the Big Freeze of 2010, when temperatures in Co. Mayo plummeted to -17.5°C. Such events can appear to contradict the broader picture. If winters are warming so fast, how did that happen so recently?
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The explanation lies in the jet stream, a fast-moving band of air high in the atmosphere that plays a central role in shaping Irish winters. When the jet stream weakens or meanders southwards, it can allow cold Arctic air to pour over Ireland for extended periods.
These cold snaps can temporarily obscure the longer-term warming trend. Our study teases out short-term atmospheric variations from the long-term underlying climate change signal. Once this distinction is made, a clear long-term warming trend of extreme winter temperatures emerges.
Recent cold snaps, such as the winter of 2010, were likely warmer than they would have been 50 years prior under the same atmospheric conditions. This helps explain why public experience and climate statistics do not always align. A single severe winter can leave a strong impression, even as the probability of such winters continues to decline.
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What this means for Ireland
While fewer icy mornings might reduce heating costs and improve road safety, the rapid loss of extreme cold brings about its own set of challenges. Many native plants and animals rely on prolonged cold to regulate growth and reproduction. Hard frosts help suppress pests and agricultural pathogens.
As winters warm, these controls weaken. Invasive species are more likely to survive, disease pressure can increase, and seasonal timing in ecosystems can shift. That Ireland's winters are becoming milder matters for ecosystems, agriculture and infrastructure, all of which are designed around assumptions about temperature extremes.
The rapid loss of extreme cold brings about its own set of challenges
The jet stream plays a strong role in shaping winter extremes, and its variability can obscure long-term change. Cold snaps remain possible when atmospheric conditions align, but the baseline has changed. The coldest outcomes now occur in a warmer climate than they once did.
The story of climate change in Ireland is not only about hotter summers, but also about the rapid retreat of the coldest nights.
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Dr Dáire Healy is a post-doctoral researcher in the Research Ireland Climate+ Co-Centre for Climate, Biodiversity and Water at UCD. Prof Andrew Parnell is the Met Éireann Professor of Data Science for Climate and Weather at UCD, deputy director of the Research Ireland Climate+ Centre and Director of the AIMSIR research institute for Artificial Intelligence in Meteorological Services, Innovation and Research.
The views expressed here are those of the author and do not represent or reflect the views of RTÉ
