BBC: The Australia Institute found that summer across most of the country over the past 20 years was about a month longer than in the mid-20th century, while winters had become shorter.
Between 2014 and 2018, summers were found to be about 50% longer.
“Our findings are not a projection of what we may see in the future. It’s happening right now,” the Australia Institute’s Richie Merzian said.
The country experienced a devastating bushfire season, which killed 33 people and an estimated one billion native animals.
In its analysis, the Australia Institute think tank compared official Bureau of Meteorology data from 1999 to 2018 with mid-20th century benchmarks.
It found that summer temperatures had lasted 31 days longer than in the 1950s and 1960s, while winter was about 23 days shorter.
“Summers have grown longer even in recent years, with the last five years facing summers twice as long as their winters,” Mr Merzian said.
“Temperatures which were considered a regular three-month summer in the 1950s, now span from early to mid-November all the way to mid-March.”
Mr Merzian said global warming had made Australian summers “a more dangerous ordeal” than they used to be.