Australia's summers have lengthened by as much as a month or more in the past half century, exposing people to greater fire and heat extremes and placing ecosystems and farm crops at risk.

Researchers from The Australia Institute analysed data from 70 of the Bureau of Meteorology's weather stations across southern and sub-tropical Australia, where the bulk of the population lives. They found in the past five years, summers were 50 per cent longer than they were in the mid-20th century.

"Reports that temperatures have increased by around 1 degree [with climate change] can tend to downplay the changes under way," the institute's study says. "The reality is the summers many Australians grew up with no longer exist."

The bureau will release reports on the recently concluded summer on Monday. This season ranked as the country's second-warmest summer, trailing only 2018-19, updated bureau data showed.