On the calendar, summer is defined as from the first day of December to the last day of February.

Winter on the calendar runs from the beginning of June to the end of August.

But the Australia Institute has looked at the temperatures recorded by the Bureau of Meteorology on and around December 1 from the middle of the last century. It concluded that we now reach those temperatures much earlier in the year and they last for longer.

Technically, summer lasts for three months but the summer-like heat of a previous era now lasts for about four.

The Australia Institute has done the same calculation for winter and concluded that we now cool to the temperatures we used to associate with the coldest season much later.

And we start warming up to what we used to think of as spring-like temperatures much sooner.

For Canberra, it reckons that the temperatures we used to experience in the 90 days of summer between 1950 and 1970 extended to 121 days of the "new", elongated summer of the two decades of this century.

And in the most recent years, the old summer temperatures have lasted for longer than four months.

In the same way, the old winter temperatures last for far fewer days before the season warms up so it feels like spring when it remains technically winter.

"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," Richie Merzian, the Australia Institute's Climate and Energy Director said.

"It's commonplace to hear older Australians claim summers aren't what they use do be. And they are right."

One of the consequences of shorter winters is that there is less time to burn potential fuel for fire safely.

"As the length of the bushfire summer season extends, the window to enforce bushfire management strategies, typically in winter, shrinks," Richie Merzian said.

He criticised Prime Minister Scott Morrison's government. "According to numerous modelling exercises, including those commissioned by the federal government, it is in Australia's national interest and economic interest to put in place a strong policy to reduce emissions.

"The Australian government's current policies only serve to further fuel the climate crisis."

Many scientists think conditions will continue to worsen even if emissions were reduced very soon.

"The worst is yet to come and that's regardless of what we do to reduce emissions because some warming is locked in," climate scientist, Dr Sophie Lewis of the University of New South Wales in Canberra said.

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"If we want to do something to avoid the worst impact of climate change, we really have to reduce emissions," she said.

This summer, Canberra Airport recorded maximum temperatures at 3.8 degrees hotter than the long-term average. Tuggeranong saw mean maximum temperatures 2.4 degrees hotter.

Bureau climatologist Blair Trewin said, "Clearly it was an exceptionally hot summer."

Temperature records have been broken repeatedly recently, including in the summers of 2018-19, 2016-17, 2013-14, 2009-10 and 2017-18 (hottest first).

The heatwave Canberra sweated through in January was also a new record, with four days in a row of 40 degrees or above.

On top of the heat, the dryness persists. For Australia as a whole, there have now been three winters in a row where the usual rains simply haven't happened, and that's unprecedented since records began.