The Great Barrier Reef could be dead within 20 years if greenhouse gas emissions are not curbed, scientists say.

A report by Australia's Climate Council reveals the mass bleaching event in 2016, which killed two-thirds of all coral in the northern third of the reef, will occur every second or third year by the mid-2030s if greenhouse gas emissions continue to rise at their present rate.

"Which basically will kill the reef," Will Steffen, the lead author of Cranking up the Intensity: Climate Change and Extreme Weather Events, told AAP.

This is just one of the warnings from the report, which shows how extreme weather events in Australia are shaped by climate change.

Another example is coastal flooding. Sea level rises of about 20cm have been recorded in Sydney and Fremantle during the past century.

"That doesn't sound like a lot but it's significant in that we've seen a threefold increase in flooding in both Sydney and Fremantle," Prof Steffen said.

Under current projections, sea levels will rise between 50cm and a metre by 2100.

"That means if an event is now expected to happen once in 100 years, it would occur every year," he said.

As long as coal, oil and gas burns as it does now, heatwaves, droughts, floods and fires will become more frequent and fierce, the report says.

"All extreme weather events are now occurring in an atmosphere that is hotter and wetter than it was 60 years ago," Prof Steffen said.

"There is more energy in the system to drive more extreme weather."

For example, 2013 was Australia's hottest year on record, and Prof Steffen said there was only a one-in-12,000 or 13,000 chance the record could have been reached under pre-industrial greenhouse gas emission levels.