A striking new phenomenon is emerging across the planet, with distinct regions – especially in Europe – seeing repeated heatwaves that are so extreme, according to US scientists, “they fall far beyond what any model of global warming can predict or explain”.
The effect, which is most intense in northwestern Europe, may be due to increased “wobbles” of the jet stream, a narrow band of strong winds in the upper atmosphere about 30,000 feet above sea level, moving from west to east due to the Earth’s rotation.
The jet stream affects Ireland’s weather, delivering low pressure weather systems and storms arising from sharp temperature differences where warm tropical air meets cold polar air in the mid-latitudes. Many studies suggest it is becoming “wavier”, moving northwards and increasing in speed, thereby exacerbating extreme weather events – most likely due to climate change.
In their study, published by Proceedings of the National Academy of Sciences, researchers based at Columbia Climate School provided the first worldwide map of hotspot regions, which show up on every continent except Antarctica “like giant, angry skin blotches”.
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In recent years these heatwaves have killed tens of thousands of people, withered crops and forests and sparked devastating wildfires. They conclude: “The most intense and consistent signal comes from northwestern Europe, where sequences of heatwaves contributed to some 60,000 deaths in 2022 and 47,000 deaths in 2023.″
The Arctic is warming on average far more quickly than most other parts of the Earth, which appears to be destabilising the jet stream, causing it to develop so-called Rossby waves, which suck hot air from the south and park it in temperate regions that normally do not see extreme heat for days or weeks at a time.
“The large and unexpected margins by which recent regional-scale extremes have broken earlier records have raised questions about the degree to which climate models can provide adequate estimates of relations between global mean temperature changes and regional climate risks,” the study concludes.
“This is about extreme trends that are the outcome of physical interactions we might not completely understand,” said lead author Dr Kai Kornhuber of Columbia Climate School. “These regions become temporary hothouses.”
Looking at heatwaves over the past 65 years, they identify areas where extreme heat is accelerating considerably faster than more moderate temperatures – often resulting in maximum temperatures “that have been repeatedly broken by outsize, sometimes astonishing, amounts”.
During the early summer last year, the jet stream was in effect locked for weeks over Europe. Locations to the north of it, including Ireland, experienced cooler Arctic air and areas of low pressure with increased rainfall. To the south, a high-pressure system stalled, drawing hot air from North Africa and maintaining hot, dry conditions.
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