Why is the polar vortex in the news this week?
The UK Met Office has predicted a combination of changes to the polar vortex and El Niño could bring severe weather to northern Europe this winter.
What is the El Niño?
El Niño is a naturally-occurring phenomenon in the southern hemisphere. It happens when the trade winds that blow east to west in the south Pacific weaken and warm water flows, which usually follows the same east to west pattern, reverse. An El Niño happens every two to seven years. The last one was in 2023-2024.
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It usually leads to higher temperatures globally and extreme events. Though it is naturally-occurring, global warming has exacerbated this year’s El Niño with some forecasters calling it a super-El Niño.
Sea surface temperatures in the equatorial Pacific Ocean have already surpassed the highest recorded during any previous El Niño events.
What is the polar vortex?
The polar vortex is a current of air 50 kilometres above the North Pole. It keeps the jet stream in place which drives the relatively mild winters that Ireland and Britain experience as it funnels in mild, wet weather from the Atlantic.
When it weakens, it can lead to a sudden stratospheric warming event.
This causes the jet stream to divert southwards, dragging cold easterly winds across northern Europe. If it hits an Atlantic depression, it can bring significant snow events like the Beast from the East in 2018.
What might happen if the two combine?
In northern Europe it could lead to a wetter and milder winter, but following the peak of El Niño, the polar vortex can become weaker.
This increases the likelihood of a Sudden Stratospheric Warming (SSW) event. An SSW can lead to a prolonged period of very cold, dry weather from the east. Alternatively, if low pressure lurks on the boundary of the weather system, the combination could trigger significant snow storms.
What are the chances of that happening?
The UK Met Office has cautioned against assuming the worst-case scenario.
In response to some doomsday reporting, it clarified: “These are shifts in probability rather than guarantees. El Niño does not determine individual weather events, and the current forecast does not support the suggestion that the UK is about to be ‘smashed’ by widespread snow associated with changes to the polar vortex.”
Met Éireann has been even more cautious, saying: “The global mean temperature tends to be higher than average under El Niño conditions, usually with a time lag of several months.
“While El Niño has clear impacts on many regions worldwide through teleconnections (for example affecting monsoon systems), its influence on Ireland and Europe is comparatively weak, highly variable, and not robust in the present-day climate.”
[ How worried should we be about this year’s ‘Super-Duper El Niño’?Opens in new window ]
