The nation’s weather largely returned to typical levels in autumn after the Black Summer’s destructive bushfires and storms, but a clear long-term trend towards more frequent extreme weather remains, the latest Australian Actuaries Climate Index reveals.

The index, released today, shows the 19th consecutive season to record a positive index value for Australia as a whole, representing higher measures and a long-term progression to a more extreme climate.

“Climate change is expected to have major environmental, economic and social impacts, and poses a serious risk to the industries that actuaries advise," Actuaries Institute CEO Elayne Grace said.

The overall index has not been negative nationwide since 2015 versus the reference period of 1981 to 2010. Sea levels – which fluctuate less dramatically than other categories and are influenced by wider storm patterns and astronomical high tides – drove the latest index increase.

During autumn, multiple regions experienced the first below-average extreme high temperature value in many years as cooler weather was observed in south eastern parts of the country. These areas included the Central Slopes, the Murray Basin, the South & Southern Western Flatlands and Tasmania’s Southern Slopes.

Extreme rainfall was below the reference period average for most of the country, especially the north western parts of Australia.

Parts of the southeast did experience above reference period average extreme rainfall as ex-tropical cyclone Esther struck Victoria in March, bringing with it the largest amount of rainfall for that month since 1929 and creating the highest extreme rainfall value ever for the Murray Basin region.

The “Consecutive Dry Days” category was below the reference period in most regions, also reflecting an increase in rainfall.

The Actuaries Institute says the return to relative normality in weather metrics in Autumn was influenced by the El Niño– Southern Oscillation (ENSO) and Indian Ocean Dipole (IOD) remaining neutral.

It notes though that there are some early indicators that a La Nina may form in spring, with the Bureau of Meteorology estimating the likelihood at 50%, which is twice the normal likelihood.

This would result in above average winter and spring rainfall in Australia, particularly in the eastern and northern parts of the country, which may continue into summer, it says.

The index monitors cyclical weather patterns to provide insights into the potential links to natural perils.

Launched in late 2018, it measures extreme weather conditions and sea levels across Australia, and how these vary over time, showing changes in the frequency, or rate of occurrence, of extreme high and low temperatures, heavy precipitation, dry days, strong winds and changes in sea levels.