Declaring a La Nina event is “jumping the gun” according to experts on climate science and atmospheric science.

University of Melbourne’s Andrew King and Kimberley Reid have published an article outlining why unofficial media reports can be harmful.

Last week, Sky News Weather Meteorologist Rob Sharpe declared Australia's fourth La Nina in five years is underway, as he warned a major state is bracing for further heavy rain this summer.

But King and Reid are wary.

“At the moment, some of the indicators used to track the state of the Pacific are just breaching the thresholds used for a La Niña event,” they said. 

“This has led to discussion in some media outlets that we’re heading into a “rare summer La Niña”.”

La Niña events are characterised by below-average temperatures in the central and eastern tropical Pacific Ocean and warmer waters in the west, nearer to Australia. They often, but not always, bring wetter conditions for eastern and northern Australia. 

Some studies suggest we should expect stronger La Niña events and stronger rainfall responses the planet warms.

In contrast, El Niño events usually bring drier weather to most of the continent.

Lower sea surface water temperatures in the central Pacific Ocean are leading to speculation about a La Niña event starting to form, raising the risk of wet weather. 

Image - Bureau of Meteorology

King and Reid say that would be unusual because La Niña events typically start in winter and get going properly in spring before “decaying” in late summer and autumn, according to the experts.

“Given the time of year, it would be hard for a proper La Niña event to get going now,” the report reads. 

“But the Bureau of Meteorology’s outlook does point to a probable wet end to summer over most areas of Australia.”

However, King and Reid say there are numerous challenges in monitoring and predicting El Niño and La Niña events.

“Keeping track of how the drivers of Australia’s climate are evolving is tricky. Climate change makes it even more complicated.

“The rapid warming of our oceans means the characteristics of La Niña events may well be changing. 

“Just identifying if we are in a La Niña is trickier than it used to be, so new measures to keep track of the El Niño-Southern Oscillation (ENSO) may become more useful.

“It’s worth noting that a criterion for a La Niña event is sustained cooler-than-normal conditions in the central Pacific because there is some week-to-week fluctuation in sea surface temperatures.

The Bureau of Meteorology (BoM) has not declared a La Niña and instead notes that the ENSO is currently “neutral” (neither El Niño nor La Niña).

“Any unofficial declaration of a La Niña is jumping the gun,” King and Reid’s report says.

“The Bureau’s long-range forecasts are the best source of information for Australians wishing to know what weather and climate conditions the next few months may bring.”