But the Australian Climate Council has warned that the cooler weather associated with La Niña will be temporary and will not slow the advance of hotter, drier weather for Australia.
The Bureau of Meteorology declared on Tuesday, September 29, that La Niña has developed in the Pacific Ocean, upgrading from a La Niña alert status to an active event.
This means that recent changes in ocean temperatures and weather patterns over the Pacific are now likely to remain until at least the end of the year.
La Niña is the cool phase of the El Niño Southern Oscillation. It is associated with cooler than average sea surface temperatures in the central and eastern tropical Pacific Ocean.
La Niña events often form in autumn or winter, then decay in late summer. The greatest impact normally occurs during the spring and early summer period.
La Niña events normally last for about a year, however they can be shorter, or much longer.
The Bureau of Meteorology said recent observations and model forecasts showed the central tropical Pacific Ocean is now 0.8°C cooler than normal, and that has resulted in changes to trade winds and pressure patterns. Climate models suggest these patterns will continue until at least the end of the year.
La Niña typically results in above-average spring rainfall for Australia, particularly across eastern, central and northern regions. It can also mean cooler days, more tropical cyclones, and an earlier onset of the first rains of the wet season across the north.
While climate scientist Professor Will Steffen said the extra rain would be useful for spring and summer crops, the weather pattern will likely reset in January or February to resume a trend towards hotter and drier weather, representing underlying climate change.
A three-decade trend in the cooler seasons was a reduction in rainfall.
Prof Steffen said the change was principally caused by the global burning of coal, oil and gas.
A Climate Councillor based in Canberra, Prof Steffen said farmers needed to be aware of the trend and be prepared to adapt their farming practices and crop choices to cope.
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