90% Chance of the El Niño Global Weather Phenomenon Striking this Year

“It is very much odds-on for an event,” said Tim Stockdale, principal scientist at European Centre for Medium-range Weather Forecasts, who said 90% of their scenarios now deliver an El Niño. "The amount of warm water in the Pacific is now significant, perhaps the biggest since the 1997-98 event.” That El Niño was the biggest in a century, producing the hottest year on record at the time and major global impacts, including a mass die-off of corals.

“But what is very much unknowable at this stage is whether this year’s El Niño will be a small event, a moderate event – that’s most likely – or a really major event,” said Stockdale, adding the picture will become clearer in the next month or two. “It is which way the winds blow that determines what happens next and there is always a random element to the winds.”

What is El Niño?

El Niño is a climate phenomenon that occurs when a vast pool of water in the western tropical Pacific Ocean becomes abnormally warm. Under normal conditions, the warm water and the rains it drives are in the western Pacific.

El Niño occurs every few years. Its most direct impacts are droughts in normally damp places in the western Pacific, such as parts of Indonesia and Australia, while normally drier places like the west coast of South America suffer floods. But the changes affect the global atmospheric circulation and can weaken the Indian monsoon and bring rains to the western US.
It is not certain what tips the unstable Pacific Ocean-atmosphere system into El Niño, but a weakening of the normal trade winds that blow westwards is a key symptom. In 2014, the trigger may have been a big cluster of very strong thunderstorms over Indonesia in the early part of the year, according to Dr Nick Klingaman from the University of Reading in the UK.

An El Niño is officially declared if the temperature of the western tropical Pacific rises 0.5C above the long-term average. The extreme El Niño year of 1997-98 saw a rise of more than 3C.

El Niño is one extreme in a natural cycle, with the opposite extreme called La Niña. The effect of climate change on the cycle is not yet understood, though some scientists think El Niño will become more common.