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| False-colour images provided by Nasa compare Pacific Ocean water temperatures from the El Niño in 1997 (right) and the current El Niño. Photograph: AP |
El Niño is one of the most predictable climate events on the planet, according to the US National Oceanic and Atmospheric Administration, but it also has a way of keeping climate scientists guessing.
In March the oceanographers predicted the current event could be the weakest on record, but in August the same agency warned it could be the strongest.
Right now it still looks strong, says Nasa's Jet Propulsion Laboratory (JPL) in Pasadena, California. Using satellite data, meteorologists keep a steady watch on El Niño because it can play out demurely, or it can bring catastrophe. It has been linked to drought and harvest failures on the African continent, devastating fires in the normally moist rainforests of the Indonesian archipelago, both drought and flood in Australia, damaging floods in the Americas, and unusually mild winters in Europe.
This month, tens of thousands of people have been forced to flee their homes in the border areas of Paraguay, Uruguay, Brazil and Argentina due to severe flooding in the wake of heavy summer rains brought on by El Niño. Paraguay's national emergencies office has said the flooding is "directly influenced by the El Niño phenomenon, which has intensified the frequency and intensity of rains".
El Niño is a blister of sea surface heat that every few years floats eastwards across the tropical Pacific Ocean. It was given its name by the fishermen of Peru, who called it "the Child" because they became aware of it around the Christmas season, as the fish catches failed. The shift of warm seas leaves the western Pacific cooler, and both temperature shifts seem to play out in disruption of global weather patterns.
The last great El Niño, in 1997-98, helped make 1998 the then warmest year on record – that too was accompanied by a series of devastating events around the world, among them ice storms in North America, floods on the west coasts of the Americas and forest fires in Borneo. It also delayed the monsoon rains in India, warmed tropical waters so severely that coral reefs started to "bleach" and die, and signalled a record-breaking season of typhoons and tropical cyclones in the eastern Pacific.
Although researchers are fairly sure that climate change as a consequence of the combustion of fossil fuels, and the release of greenhouse gases, could make El Niño more frequent, or more devastating, or both, it remains a natural, cyclic event. Climate historians have linked it, with sometimes faltering levels of confidence, to historic events, among them the epidemic of Spanish influenza that claimed millions of lives in 1918 and even the Biblical plagues of Egypt linked to the story of Moses.
Sometimes oceanographers watch an El Niño develop, and then fade gently. And sometimes it develops powerfully, with consequences for the rest of the globe. Oxfam has already warned that this time millions could face famine as a consequence.
However, as the rains fail in Africa, Californians – still in the grip of a prolonged and damaging drought – may see a silver lining. In 1997 and1998 storms slammed into the US west coast, crossed the mountains, drenched Texas and even hit Florida. This time, El Niño may be seen as bringing relief.
"The water story for much of the American west over most of the past decade has been dominated by punishing drought," said JPL climatologist Bill Patzert. "Reservoir levels have fallen to record or near-record lows, while groundwater tables have dropped dangerously in many areas. Now we're preparing to see the flip side of nature's water cycle – the arrival of steady, heavy rains and snowfall."
What a heat bubble on the eastern Pacific – where the much warmer water means that a great stretch of ocean is actually up to 25cm higher than the cooler waters north and south of it – means for the UK is much less certain. "There are a number of factors that affect winter conditions in Britain," the Met Office said earlier this year. "The increase in risk of a colder winter this year from the developing El Niño is currently considered small."
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