The Australian Bureau of Meteorology has declared the end of the El Niño climate phenomenon for 2023-24, reports Guardian. Since 1910, there have been 29 El Niño events, a phase in which easterly equatorial winds in the Pacific are slowed or even reversed.
The opposite pattern, La Niña, has stronger easterly winds than usual. In the past 114 years, there have been 20 La Niña events, according to the bureau.
Carl Braganza, the bureau's chief of climate services, outlined the main characteristics of a completed El Niño and what comes next.
How strong was El Niño?
Sea surface temperatures in the Pacific Ocean, where the El Niño phenomenon originates, peaked last November with an anomaly of about plus 2.1C. By comparison, the 1997-98 El Niño, considered perhaps the strongest on record, recorded temperatures about 2,5C above normal.
"The atmospheric component of the recent El Niño was relatively weak compared to the 1997-98 event or even the previous El Niño of 2015-16," says Braganza.
Was El Niño the primary climate driver?
By September, when the bureau announced that El Niño was in effect, longer-term forecasts already indicated that eastern Australia's summer might not be unusually dry.
This is because Australia's climate is influenced not only by Pacific climate patterns, but also by the Indian and Southern Oceans.
As the spring ended, the southerly influence became more important as a very strong positive phase of the Southern Annular Mode (SAM) – marked by westerly winds contracting towards the Antarctic – took hold.
Will the La Niña phenomenon follow?
International climate models, including those of the bureau, predict that neutral conditions in the Pacific Ocean will continue through the Southern Hemisphere winter. However, La Niña is expected to kick in later this year.
The US National Oceanic and Atmospheric Administration estimates a 60% chance of La Niña starting between June and August. However, Braganza emphasizes that the phenomena at this time of the year have relatively low indicators.
"So far, we're really looking at what Pacific temperatures are likely to do in the models. The atmosphere has yet to be coupled to real-world oceanic conditions, and this is not a given. A string of three consecutive La Niña years – as happened between 2020-21 and 2022-2023 – followed by an El Niño and then another La Niña would be something new, at least according to the historical record,” he says.
What role does climate change play?
Another big reason meteorologists are cautious about predictions is how global warming could affect weather patterns.
“We have climate change trends going on in the background. We haven't seen ocean temperatures like this before, so we just have to be a little cautious. All of these factors are why using a climate model that collects millions of observations in real time is the best guide we have," says Braganza.