The UK could be in for a wet and stormy autumn followed by a colder, calmer winter – and an unusually powerful El Niño may be partly responsible.
El Niño is a natural climate pattern in the tropical Pacific, but its effects can be felt around the world. This year’s event is already the strongest on record, and is expected to strengthen further before peaking later this year.
El Niño is the warm phase of the El Niño Southern Oscillation, a natural cycle involving the tropical Pacific Ocean and the atmosphere. During El Niño, unusually warm sea-surface temperatures in the central and eastern Pacific reverse the direction of certain winds, affecting weather patterns far beyond the region. A stronger El Niño has a larger influence on global weather patterns than a weaker one.
So how does a climate pattern thousands of miles away affect the weather in the UK and Europe?
How El Niño reaches Britain
The link between El Niño and weather in the UK is complicated and not direct. Weather systems in different parts of the world can influence one another through links known as teleconnections. El Niño has teleconnections both in the troposphere, the part of the atmosphere we live in, and the stratosphere, the part of the atmosphere just above us.
Through these teleconnections, El Niño is linked to the North Atlantic oscillation, a weather pattern which involves differences in air pressure over the ocean. El Niño is associated with the oscillation’s negative phase, when this pressure difference is less than usual. This tends to weaken the winds that bring mild air from the Atlantic to the UK, increasing the chance of colder, calmer weather in late winter.
El Niño can also affect the stratospheric polar vortex, a band of strong winds that circles the Earth high above the Arctic. It has been found to weaken the vortex which then can disrupt the jet stream – the high moving body of air that is a driver behind much of the UK’s weather. This can increase the chances of storms and wetter and potentially colder weather in the autumn and early winter.
Vortex weakening is also linked with an increase in sudden stratospheric warming events, when parts of the atmospheric layer above ours warm up rapidly. These events are one driver of some cold snaps in the UK as they can alter the jet stream and allow colder air to reach the country. However, not all of these events result in cold weather in the UK.
These links are relevant to the UK’s latest seasonal forecasting from the Met Office. This forecast shows autumn is likely to bring wetter and stormier weather followed by colder, calmer weather in winter.
Colder, calmer weather in UK winters is known to present a challenge for energy production from renewable sources, especially when it is also cloudy. Wind power generates 40% or more of the UK’s electricity during winter, and cold, calm periods can require more gas power to make up for lower wind generation and increased demand for heating.
El Niño also improves our ability to [predict weather at long lead times] because of its links with major drivers of different weather patterns. This includes for winter weather but also in some cases summer heatwaves. There are limits, however: we cannot tell when a particular heatwave or storm will occur. We cannot predict the associated impacts in detail. We can only say whether a certain season is more likely to be hotter or drier or colder or wetter, and identify related trends in impacts.
It is important to remember that two things happening at the same time do not mean they cause one another. In the case of El Niño and the weather in the UK, the response is non-linear and not direct.
There is little evidence yet about whether human-induced climate change is causing more intense or more frequent El Niños. But it certainly amplifies the warming effect of climate change. Some research suggests that it can also amplify climate whiplash, where some regions flipflop from wet weather to hot-dry weather either within seasons or in one season after another.