Australian summers have become, on average, 31 days longer in Australia's capital cities, and in regional areas that number is even higher, according to a new report.

Researchers at the Australia Institute crunched Bureau of Meteorology (BOM) data from between 1999 to 2018 and compared it with Australian weather records from 1950 to 1969.

The analysis found all Australian capital cities experienced longer summers and shorter winters, with summer 31 days longer and winter three weeks shorter than in the 50s and 60s.

In regional areas the trend was even more pronounced — including the NSW town of Port Macquarie, on the Mid-North Coast.

Two researchers examined the BOM data from 70 weather stations across the non-tropical parts of Australia.

The discussion paper, titled Out of Season, concluded climate change had led to significant changes in Australian seasons.

Australia Institute Climate and Energy Program director Richie Merzian said average temperatures previously recorded around the start of December were setting in much earlier.

"If summer feels like it's getting longer and longer, it's because it actually is, especially if you're an older Australian," Mr Merzian said.

"Those average summer temperatures are starting a lot earlier and they're finishing a lot later, so summers have become twice as long as winters in the last five years."

The Australia Institute is a non-partisan organisation which conducts research on matters of public policy.

The discussion paper found Sydney was experiencing an extra 28 days of summer and 15 fewer days of winter, compared to the 50s and 60s.

Summer came earlier in the nation's capital too, with 35 more summer days recorded in Canberra in the past five years and 35 fewer days of winter.

Melbourne has had an additional 38 days of summer temperatures and 19 fewer days of winter.

To calculate these results, researchers worked out what the average temperature was for the start of summer in the 50s and 60s and then determined what the date was when the same temperature was reached in the past two decades.

The Lindfield Park Road fire near Port Macquarie first ignited in July 2019 and burnt for almost seven months.

Responding to the report, NSW Rural Fire Service Mid Coast District Officer and Port Macquarie resident Stuart Robb said bushfire seasons would also get longer as temperatures increased.

"This would put additional pressures on landholders and agencies to undertake hazard reduction works ahead of the summer months," he said.