Every two to seven years, the equatorial Pacific Ocean gets up to 3°C warmer (what we know as an El Niño event) or colder (La Niña) than usual, triggering a cascade of effects felt around the world. This cycle is called the El Niño Southern Oscillation (ENSO) because every El Niño is naturally followed by a La Niña and vice versa, with some months of neutral conditions in between events. The change in sea surface temperature associated with ENSO events might seem marginal, but it is more than enough to disrupt weather patterns globally and even the large-scale circulation of air in the polar stratosphere 8km above the Earth.
It is not surprising for La Niña conditions to last two consecutive years, but a three-year La Niña, which the world has had since 2020, is more rare. The US National Oceanic and Atmospheric Administration (NOAA) has reported that the equatorial Pacific Ocean will return to its neutral state between March and May of 2023, and it is likely that El Niño conditions will develop during the northern hemisphere’s autumn and winter.
