1. The year that’s just closing will have been, very probably, the hottest year on record, and in Britain and the US it’s been one of the warmest – and wettest – winters.
That’s partly due to climate change. But there’s been another factor: “El Niño”.
Every few years – between two and seven, on average – a huge swath of the Pacific Ocean heats up near the equator. It pumps enough energy into the air to warm the entire atmosphere. That’s El Niño, and it is part of a vast global climate cycle known as the El Niño Southern Oscillation (ENSO). “It drives weather patterns globally,” says Prof Adam Scaife, the head of long-range forecasting at the UK Met Office and an expert on El Niño patterns. “It’s the biggest fluctuation in global climate patterns.”
Waves crash over the Cobb at Lyme Regis, Dorset, as Storm Frank begins to batter the UK on its way towards flood-hit areas.
3. In western Europe, one thing that El Niño does is cause warm, wet, stormy weather at the beginning of winter.
There are other factors at play, says Scaife, but both climate change and El Niño increase the risk of major storms like those which have flooded parts of England in the last few weeks.
It may not last, though. “Later in the winter, El Niño is associated with colder, more blocked conditions,” he says.
5. What’s more, this isn’t just any El Niño. It’s a whopper.
“The big news is that this is the largest El Niño in 20 years,” says Scaife. “It’s 3°C above normal, and it’s peaking right now.
“What will happen is that that warmth will spread across the globe, and add to the effects of climate change.”
6. Which is why this year has been such a scorcher – and why next year, almost certainly, will be too.
Scaife says that 2015 “is at or near record temperatures. That’s mainly climate change, but El Niño is affecting that.” The Met Office, NASA, and the US National Oceanic and Atmospheric Administration all agree on that. What’s more, it follows 2014, which was itself a record year – without the input of El Niño – and because El Niño will drag on until next year, 2016 is predicted to be even warmer. “By the end of 2016, we may have had three records in a row,” Scaife warns.
A bridge in Tadcaster, North Yorkshire, which has collapsed in the floods.
8. Britain is struggling with devastating floods, which can be partly blamed on El Niño. But other parts of the world may be even worse affected, and less able to deal with it.
Scaife says that Australia, South Africa, and northern Brazil are all at risk of severe drought in the next few weeks, while Argentina and the eastern United States are facing the risk of floods.
All this has been observed in earlier El Niño years, he says, and is also predicted by Met Office climate models. “When you get that agreement between theory and observation, you can be pretty confident.”
9. And we can expect more of this in future, because while El Niño comes and goes, the effects of climate change will keep building up.
The ENSO cycle is part of what’s called “natural variability”, the semi-random, semi-cyclical ups and downs that the climate goes through anyway. But underneath all that, there is the steady impact of increasing global temperatures.
“When these natural factors add to underlying climate change, that’s when you get these unprecedented events,” says Scaife. A big upward bump added to the slow increase caused by climate change is enough to cause these really extreme events – especially, he points out, since climate change is also expected to increase rainfall, because warmer oceans means more water evaporating from the surface and forming rainclouds.
El Niño as observed by the TOPEX/Poseidon satellite mission in 1997. The 1997/98 El Niño was another huge one, which was part of the reason that 1998 was one of the hottest years on record. The white areas show the pool of warm water in the Pacific.
11. After next year, it may die down for a while. But we can expect more of this sort of thing in future.
This El Niño will come to an end in the first half of 2016, and 2017 will most likely not be as warm. But behind that natural, temporary cooling, the steady warming impacts will continue, and next time El Niño comes around, we can reasonably expect more of the same.