Australia was already a land of extremes but it's hotter than before with a greater risk of more heatwaves and more severe weather.

The Climate Commission says the length, extent and severity of the present heatwave is unprecedented and shows climate change is making extreme heat and bushfires worse.

It says the impact needs to be understood to plan for more of the same.

In a report called Off the charts: Extreme Australian summer heat, one of the authors, David Karoly, says the heatwave has affected over 70 per cent of Australia and longstanding temperature records have been broken.

"Although Australia has always had heatwaves, hot days and bushfires, climate change is increasing the risk of more frequent and longer heatwaves and more extreme hot days, as well as exacerbating bushfire conditions," Professor Karoly said in a statement.

"The baseline conditions have shifted.

"We live in a hotter world and the rise of more frequent and severe extreme weather has already increased."

The current conditions are unusual because of their widespread nature and duration, the report says.

Heat is a "silent killer" because small changes in the environment can have dramatic impact on the human body.

The report says if the core body temperature exceeds 38 degrees Celsius for several hours judgment and behaviour can be impaired.

Heatwaves in recent years have resulted in increased hospital admissions and death.

The Climate Commission says having a good understanding of climate change risks can ensure that action is taken to reduce greenhouse gas emissions and plans are made to respond to more extreme weather.