A ‘super’ El Niño is on the way: what does it mean for the climate?

The name comes from seventeenth-century Peruvian fishermen, who noticed that this warming often appeared around Christmas: they named it after the Christ Child (‘El Niño’ means ‘the boy’ in Spanish). During the opposite phase, known as La Niña (‘the girl’), the same waters instead become colder than normal. There is also a third, neutral phase, during which temperatures return to average. The phenomenon’s full name also includes the word ‘oscillation’ because, together with sea temperatures, atmospheric pressure also changes between the western Pacific, near Australia, and the eastern Pacific, near the Americas. Normally, when pressure is higher in the east, winds push warm waters westwards, allowing cold, nutrient-rich water to rise from the depths along the American coasts. From time to time, however, the situation reverses: higher pressure shifts westwards, the winds weaken and warm water remains in the eastern Pacific. This is precisely the sign that El Niño has returned.

What makes an El Niño a ‘super’ El Niño? An El Niño is officially declared when the sea-surface temperature in the eastern equatorial Pacific remains at least 0.5°C above average for several months. But when the waters rise more than 2°C above average, it is considered a truly exceptional event: a ‘super’ El Niño. Since last April, temperatures in that part of the ocean have remained well above average, and in June scientists began to grow concerned: according to the latest forecasts, there is a 63% chance that temperatures this winter will exceed 2°C above average, signalling an approaching super El Niño. Some computer models predict ‘surprisingly high’ global temperatures for November and December. One interesting detail is that global warming, caused by human activity, now makes it more difficult to detect the onset of an El Niño because average temperatures are already higher than in the past. Scientists have therefore had to update their forecasting tools so that they can distinguish El Niño’s contribution from that of general global warming. A strong El Niño can have very significant consequences: the additional heat transferred from the ocean to the atmosphere can cause a surge in heat-related health problems and encourage the spread of mosquito-borne diseases such as cholera, typhoid and malaria. El Niño also alters the path of the jet stream - a band of very strong high-altitude winds - making some parts of the planet drier than normal and others wetter. In the United States, for example, more numerous and intense cyclones are expected in the Pacific, while Atlantic hurricanes may find it more difficult to form. The good news is that each El Niño event lasts for a relatively short time: it usually develops in summer, strengthens during winter and fades by the following spring. The strongest previous El Niño events occurred in 2015-2016, 1997-1998 and 1982-1983. The 1997-98 event remains the most powerful ever recorded: it temporarily raised the global average temperature by 1.5°C and triggered devastating weather events around the world, including torrential rain and flooding in Peru and East Africa, drought-fuelled fires in South-East Asia, storms and landslides in California, and the bleaching of around one sixth of the planet’s coral reefs. The economic costs were also enormous: the 1982-83 event is estimated to have cost the world around 4.1 billion dollars, while the 1997-98 event is thought to have caused damage amounting to approximately 5.7 trillion dollars. It is not yet clear how strong this year’s event will be. But, as climatologists point out, given the global warming already under way, it would not even take an exceptionally strong El Niño to break this year’s heat record.