The Bureau of Meteorology has declared the El Niño weather event of 2023-24 to be over, with odds increasing that its cooler counterpart, the La Niña, will return by the coming spring.
Conditions in the central equatorial Pacific have now returned to neutral conditions, about seven months after the El Niño had got under way, the bureau said on Tuesday.
For Australia, an El Niño typically delivers below-average rainfall for much of the country’s east, while La Niñas are associated with wetter than usual weather for northern and eastern parts during the winter-spring period, the bureau said. August to October was Australia’s driest three-month period ever recorded by the bureau.
The El Niño-Southern Oscillation – which gauges air pressure differences between Darwin and Tahiti – is one of the key drivers affecting global climate.
“International climate models suggest ENSO is likely to continue to remain neutral until at least July 2024,” the bureau said, adding the main climate models it uses are predicting a La Niña may form by spring if not before.
Climate models, though, are pointing to a La Nina forming, perhaps by September. (There is an autumn 'predictability barrier' - so forecasts need to be taken with some caution.) pic.twitter.com/KGQf79muMT
— @phannam@mastodon.green (@p_hannam) April 16, 2024
Should a La Niña get under way later this year it would be the fourth such event in the past five years. Such a sequence – of three La Niñas followed by an El Niño and La Niña – hasn’t been recorded previously, Cai Wenju, a former senior CSIRO researcher, told Guardian Australia earlier this year.
Other agencies have also been forecasting the possibility of a La Niña event later this year. The US’s National Oceanic and Atmospheric Administration, for instance, last week put the odds of a La Niña at about 85% although its thresholds are slightly lower than the bureau’s.
La Niñas typically see a strengthening of the easterly equatorial winds, shifting rainfall patterns towards Australia and south-east Asia. The number of cyclones affecting Australia are usually above average during La Niña years.
The Pacific tends to absorb more warmth than during El Niño years, exacerbating the background warming from climate change.
“Global sea surface temperatures (SSTs) have been the warmest on record for each month between April 2023 and March 2024,” the bureau said. “Month-to-date data for April 2024 indicates this month is tracking warmer than April 2023.”
The bureau noted that predictions made in mid-autumn “tend to have lower accuracy than predictions made at other times of the year. This means that current forecasts of the ENSO state beyond July should be used with caution”.
That run of record-breaking heat might also add to the uncertainty about how conditions evolve in the Pacific and the resulting weather impacts.
“The global pattern of warmth is affecting the typical historical global pattern of sea surface temperatures associated with ENSO variability,” it said. “As the current global ocean conditions have not been observed before, inferences of how ENSO may develop in 2024 that are based on past events may not be reliable.”
