Australians face the prospect of sweating through more intense heatwaves, and being swamped by more frequent downpours of heavy rain in the coming decades as a result of climate change.

The worrying predictions are contained in the fifth annual biennial State of the Climate report prepared by scientists at the CSIRO and Bureau of Meteorology released on Thursday.

Using the latest scientific data on trends in Australian temperatures, rainfall, fire weather and ocean conditions, they discovered Australia has warmed by more than 1C since records began in 1910 as carbon dioxide levels in the atmosphere climb to record levels.

They predict more extremely hot days on land will be accompanied by rising temperatures in the seas off Australia's coast, including the waters of the Great Barrier Reef where back-to-back coral bleaching occurred in 2016 and 2017 as a result of warmer conditions.

But there's also expected to be more intense heavy rainfall throughout Australia, particularly for short-duration extreme rainfall which raises the risk of damaging floods.

"As the climate warms, heavy rainfall is expected to become more intense, based on the physical relationship between temperature and the water-holding capacity of the atmosphere," the report said.

"For heavy rain days, total rainfall is expected to increase by around seven per cent per degree of warming.

"For short-duration, hourly, extreme rainfall events, observations in Australia generally show a larger than seven per cent increase."

The scientists behind the report say that while there's already evidence that downpours are becoming more intense, overall rainfall between May and July in Australia's southwest has dropped 20 per cent since 1970.

In the southeast, rainfall has eased by 11 per cent between April and October.

"The drying in recent decades across southern Australia is the most sustained large-scale change in rainfall since national records began in 1900," the report said.

The drier conditions are likely to bring with them more droughts and an increase in the number of high fire weather danger days, as well as longer fire seasons for southern and eastern parts of the country.

One of the report's authors Dr Helen Cleugh said the aim of the document was to provide credible information to help Australia's adapt to climate change risks.

"We certainly find that the impacts associated with these long-term trends that we are seeing have an impact on Australia's environment, economy, our people and health of our ecosystems, and so that is certainly a concern," she told reporters.

While the Earth has already warmed 1C since the 19th century, experts fear if it heats up by another 1.5C or 2C there will be more heatwaves, water shortages and flooding.

Under the 2015 Paris agreement, countries are required to limit their greenhouse emissions to limit global temperature rise this century to below 2C, with an aspirational target of 1.5C.