El Niño has been declared by the US National Oceanic and Atmospheric Administration, marking the start of a natural climate phenomenon that will influence weather patterns right across the Pacific Ocean.
In a statement, NOAA said “El Niño conditions are present and are expected to gradually strengthen into the winter”. It suggests there is an 84% chance of a moderate El Niño by the start of the northern hemisphere winter and a 56% chance of a strong event.
Normally, trade winds in the eastern Pacific Ocean push warm water at the ocean’s surface west towards Asia and Australia. This causes cold water from the ocean’s depths to rise near South America.
El Niño – sometimes described as the Southern Oscillation or El Niño-Southern Oscillation (ENSO) cycle – occurs when these trade winds diminish, causing warm water to be pushed back toward the Americas.
The knock-on effects of this process can have major impacts on human lives. Beyond changes to climate in nations bordering the Pacific Ocean, changes to cold water upwelling off South America are typically unwelcome by local fishing industries, as warm waters are less nutrient-rich and can see fish stocks reduce.
El Niño typically changes weather patterns across many nations in or along the Pacific.
Wetter than average conditions become more likely for America’s southwest coast and along the Gulf of Mexico, while the northern US could be expected to have warmer winters and reduced rainfall from the Pacific Northwest across to the Ohio Valley.
Scientists are also increasingly warning of the effect climate change may have on climate phenomena.
“Climate change can exacerbate or mitigate certain impacts related to El Niño,” says Michelle L’Heureux from the NOAA Climate Prediction Center.
“For example, El Niño could lead to new records for temperatures, particularly in areas that already experience above-average temperatures during El Niño.”
For southern hemisphere regions, El Niño can present different conditions. For South American countries along the Pacific coast like Ecuador and Peru, it’s typically associated with increased rainfall and flooding. Some parts of central Chile may also experience increased precipitation.
It’s a different story in Australia and Asia where El Niño generally means reduced end-of-year rainfall. That’s bad news for southern parts of Australia that typically expect hot summers and encounter far drier conditions, and heightened fire and overnight frost risk.
Earlier this week, Australia’s weather bureau upgraded its El Niño watch status, but is yet to formally declare the emergence of the climate event.
“El Niño generally promotes hotter and drier conditions in Australia and increases the risk of drought and bushfire,” says Ruby Lieber from the ARC Centre of Excellence for Climate Extremes.
“While the tropical Pacific Ocean has warmed to El Niño thresholds, the atmosphere is not responding in the way typical of an El Niño. Every El Niño is different and so we cannot be certain as to what the weather and climate will do in response.”