Alissa MacMillan
Q: My aunt keeps talking about El Niño and how worried she is about its impact on the climate this coming year. Is there cause for concern?
A: With the summer that’s nearly behind us, in particular the many heat waves across Europe, it only makes sense that your aunt would look for an explanation and even some insight about what’s to come.
And while El Niño is on the minds of many of us, it’s a naturally occurring weather pattern that happens every two to seven years, explains Paul Moore, a climatologist with the Climate Services Division of Met Eireann. It’s one of many “oscillations,” or periodic changes in sea surface temperatures. El Niño refers to warmer sea surface temperatures in the central and Eastern tropical Pacific, while its counterpart, La Niña, refers to colder sea temperatures there, these variabilities having an effect around the globe.
“El Niño, especially in equatorial regions, tends to lead to similar patterns each time,” Moore explains, including drier spells in the south of Africa, Indonesia, Australia, and parts of South America and wetter weather in the Horn of Africa, the central west Pacific, and the Southern US during the winter. While these effects are “locked in every time closer to the equator,” Moore adds, in the mid-latitudes, where we are, “it’s not that simple, it depends on everything else.”
For us, El Niño has more influence in winter, “a strong El Niño tending to lead to a wetter, milder late autumn and early winter and a colder and drier late winter for northwest Europe.” Of course, he adds, “that’s what tends to happen, but it’s not as straightforward as that.” The numerable atmospheric circulation systems are connected and interacting in varied ways. They are, as Moore says, “teleconnected.”
“In terms of the summer that’s gone, with El Niño and the mid-latitudes, for us in northwestern Europe, it’s highly variable what effect it has had. It interacts with other global drivers that can be stronger for us.” What happened and what’s to come weather-wise is a matter of how El Niño interacts with other large-scale climate patterns, like the Stratospheric Polar Vortex, the Arctic Oscillation, and the North Atlantic Oscillation.
For example, what Moore noticed over the summer, which might be a tentative link to the heat waves, was a stagnation of the Madden-Julian Oscillation (MJO), a disturbed area of weather around the equator which moves through different phases from west to east, starting off in the Indian Ocean and moving through Indonesia out to the Pacific. “It’s a periodical atmospheric disturbance going on all the time and it can be strong or not strong depending on different factors,” he explains. “If it’s strong and it moves over the Pacific, it teleconnects to increase high pressure at certain times of year, especially over northern Europe.”
But, Moore noticed, “during the summer, because of El Niño, the MJO was kind of stuck in the Pacific because that’s where the warm water is,” activating, dying out, and reactivating, but not going anywhere else, this also teleconnecting, leading to more high pressure for northern Europe.
“Another fly in the ointment is the Indian Ocean Dipole (IOD),” Moore adds, an oscillation of sea surface temperatures in that region. If it’s in a “positive phase,” when the ocean temperature is warmer, it brings warmer waters toward Africa, cooler waters toward Asia, and this “teleconnects” with wetter, windier conditions for late autumn and early winter in northwest Europe. The IOD is developing into a positive phase now, he says, helped by El Niño. This can also have a strong influence on weather, acting to increase the strength of the Atlantic jet stream.
WETTER, WINDIER LATE AUTUMN ON THE WAY
While these varied oscillations are at work, we are already in one of the strongest El Niños on record, and it’s still strengthening – it normally peaks in November and February and should slowly die down through 2027. But this is with already-rising average temperatures.
“This El Niño is going to be the strongest on recorded record, on top of the background warming,” Moore says, with global warming already “locked in” at 1.4 degrees from the pre-industrial era. “It could be up to 1.7 degrees above preindustrial next year,” El Niño kicking it up even further.
With El Niño, the surface water temperature usually rises, but this time it’s been noticeably higher. “In the past it would have gone to 2.5 or 2.6 degrees above average; this upcoming one is not one we’ve seen in direct records,” looking like it will be at least 3-3.4 degrees above average, making for a possibly stronger, more impactful system and, again, a wetter, windier late autumn for us.
2026 WARMEST ON RECORD?
While the increase in temperatures will be temporary, there is still long-term impact.
“The effects in the atmosphere will linger,” he says, adding, “it will be high next year, then La Niña will likely bring the global temperatures down a bit, but it’s not going to go down to what it was before,” he says. “If we are continually burning fossil fuels, which we are, that background warming will keep going up,” El Niño and La Niña adding to weather events amid ever-rising temperatures. With a year of 1.7 degrees higher globally, more extreme events are likely.
Forecasters have also been saying that 2027 will be the warmest year on record globally, but 2026 could also surpass 2024 and become the warmest year on record first. There is normally a lag in the atmospheric temperature from the ocean temperatures, so “some now are saying, because it’s so strong coming to the end of this year – at the moment sea surface temperatures are 2.8 degrees above average – forecasts are showing a chance of 2026 being the warmest because El Niño is so strong and because it got so warm so quickly.” For Ireland, the effect of this is not as clear because of our variable climate.
Of course, all of this has an impact on climate events, in particular more extremes.
“When it’s hotter, droughts are going to be worse,” Moore explains. “Droughts are worse because the earth is also thirstier because it’s warmer air which holds more moisture. Dominated by high pressure, we also get more evaporation from the ground. When it’s wetter, we’ll get heavier rainfall events.”
So, you might tell your aunt that El Niño isn’t to blame, but it is part of a complex system, with natural and human-caused contributors, all tending to a change in the weather.
