Cyclones are expected to be less likely in the future due to climate change, though the intensity and impact of extreme weather will be greater, according to a senior climatologist with the Bureau of Meteorology (BOM).

Key points: BOM climatologist expects climate change will reduce the frequency of cyclones

BOM climatologist expects climate change will reduce the frequency of cyclones Cyclone intensity and impact expected to increase

Cyclone intensity and impact expected to increase Storm surges expected to become worse as sea levels continue to rise

Dr Blair Trewin has told an Australian emergency management conference in Sydney that tropical cyclones are holding more moisture and dumping more rainfall.

He said Hurricane Harvey produced record rainfall because it parked for four days over Texas in the United States.

Loading

Dr Trewin said storm surges would also become worse as a result of sea levels that were rising at 3.4 millimetres per year.

He said extreme heat events were already occurring with greater frequency and intensity, which he said were both indicators of a changing climate.

Dr Trewin said "off the scale" heat events had become more common, particularly in the southern hemisphere.

The Bushfire and Natural Hazards Cooperative Research Centre (CRC) will release its bushfire outlook for southern Australia on Tuesday.

Its northern outlook, released in late July, predicted above-normal fire potential for western and northern Queensland and Western Australia and throughout parts of the Northern Territory's centre and north.

Dr Trewin said no matter what policies governments adopted today, climate changes have been locked in for about the next 30 years.

Increased extreme heat and bushfire risks

The senior climatologist said Australia's Forest Fire Danger Index has been rising and the length of the fire season has also been increasing, with fire danger likely to increase throughout the 21st century due to climate change.

Live fuel moisture content in forest areas of the Sydney basin in July 2013 (left) and July 2017 (right). ( Supplied: The Conversation. )

He said unprecedented heat events are becoming more common, with temperatures more than four degrees above previous records.

"Two summers ago it was South Africa. Last summer it was Chile. And so far in Australia we have been lucky that we haven't seen an event in that scale in summer, in a more heavily populated area," he said.

A heatwave in Paris in 2003 led to an estimated 10,000-30,000 deaths.

"However you look at extreme high temperatures, the frequency of extreme high temperatures is increasing," he said.

Heatwaves the biggest killer

Natural hazards expert Andrew Gissing said heatwaves have killed more people in Australia than floods, cyclones and bushfires put together.

In Australia, more than 4,500 people have died in extreme heat events since 1900.

Fatalities to extreme weather: Hazard Period Fatalities High risk states Extreme Heat 1900-2011 4,555 Vic, NSW, SA Flood 1900-2015 1,859 Qld, NSW Tropical Cyclone 1900-2015 1,216 WA, NT, Qld Bushfire 1900-2011 825 Vic, NSW, Qld Wind storm 1900-2015 525 NSW, Vic, Qld Source: Andrew Gissing, Risk Frontiers

Mr Gissing said the increasing number of heatwaves posed a challenge to emergency services.

"As emergency management agencies move forward, we're going to have to get a better understanding of vulnerability in heatwaves, who are the most vulnerable people during heatwave events," he said.

In terms of rainfall, Dr Trewin said increasing extreme rain events in a hotter world is a matter of basic physics.

"The warmer the atmosphere, the more moisture it is capable of holding", he said.

However, predictions were difficult to make, Dr Trewin said, "because extreme rainfall tends to vary a great deal from year to year, you need quite a strong underlying trend to be able to get a convincing signal in the observations".

Climate locked in

The effects of greenhouse gases can take a generation to take effect, Dr Trewin said.

"The time lag between a change in an emissions pathway and its effect on climate is about 20 to 30 years," he said.

"That's largely because the oceans take a long time to catch up with the atmosphere.

"So what happens over the next 20 to 30 years is more or less locked in.

"Even the low range scenarios take us beyond where we've been before."