Steven Mew – Australian Science Media Centre

The Bureau of Meteorology (BOM) has declared a La Niña alert this week after renewed cooling in the tropical Pacific Ocean, and climate models suggest a 70% chance of a third consecutive La Niña year forming. The BOM’s La Niña alert is the last step before an official La Niña year is declared.

With reservoirs already full and farmers at breaking point, Professor Julie Arblaster from the ARC Centre of Excellence for Climate Extremes told the AusSMC that a third La Niña year is very concerning.

“Many regions are still recovering from flooding events earlier this year and additional rainfall in already saturated catchment areas could impede this recovery,” she said.

While three back-to-back years of La Niña is not unheard of, it is still a rare event, according to Prof Arblaster, who said there will be an increased likelihood of drought in California and wet conditions in the south-east of Asia.

Dr Agus Santoso from the UNSW Climate Change Research Centre added that the wet La Niña conditions have been enhanced by a climatic phenomenon in the Indian Ocean called the negative Indian Ocean Dipole (IOD).

According to Dr Santoso, a negative IOD can enhance La Niña development by strengthening the Pacific trade winds that support a La Niña.

“The negative IOD, expected to peak in spring, will likely bring higher-than-normal rainfall across the southern parts of Australia, including NSW and Victoria in the coming months,” he said.

While La Niña and El Niño seasons are part of the natural climatic cycle, it’s not yet understood how much human-caused climate change can influence the frequency and severity of these climate patterns.

As a result, Aussie experts believe further funding is needed for research into climate variation from changes in ocean temperatures, which is one of the main drivers of swings in climate patterns such as La Niña and El Niño.

Dr Roger Stone from the University of Southern Queensland emphasised that this finding is particularly important for Australians because Australia, and especially eastern Australia, is one of the most vulnerable regions around the globe with regard to the direct impacts of La Niña and El Niño.

“We know that severe, drought-inducing El Niños are very often followed by intense or protracted La Niñas – so Australia should have been prepared for this period of back-to-back severe seasonal climate patterns of extreme drought and extreme flood,” he told the AusSMC.

Despite the recent La Niña years, Prof Arblaster says the global temperatures in the 2020s have remained over 1°C warmer than the pre-industrial period, which indicates the “overwhelming influence of human influence on the climate and the urgent need to reduce emissions”.

The BOM’s latest report indicates that Australia’s climate has warmed by around 1.47 °C over the last 110 years, with a trend toward a greater proportion of rainfall from high-intensity short duration rainfall events, especially across northern Australia.