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And it will be decades before extreme temperatures stop rising due to the effects of human-induced climate change, one of the co-authors of the Australian Heatwaves report, Professor Will Stefan of the Climate Council, says.
Heatwaves are occurring up to two weeks earlier than previously recorded, are lasting longer and the number of record hot days has doubled in the last 50 years, the report says.
Scientists define a heatwave as more than three consecutive days where the temperature is in the top 10 per cent of days for that time of year, as well as being hotter than the previous month.
During the past decade there were three times as many hot-day records as there were cold, Prof Stefan said.
"That's virtually impossible to happen on the grounds of natural variability alone," he told reporters.
"What's behind this? The physics is really, really clear. The amount of greenhouse gases in the atmosphere is going up."
Co-author and heatwave expert Dr Sarah Perkins said "it is clear" heatwaves are becoming more savage and are lasting longer.
"This summer and last summer have been characterised by extreme temperatures a lot of which have been record breaking," she said.
Extended heatwaves will have significant negative impacts on health and infrastructure, co-author Professor Lesley Hughes said.
"Heatwaves have been dubbed the silent killer," she said.
About 1000 people in Australia, generally elderly or children, die each year due to heatwaves.
In the 2003 European heatwave about 70,000 people died and in Russia in 2010 more than 50,000 were killed by extreme heat.
Heatwaves also damage infrastructure, Prof Hughes said.
Roads can melt, train and tram tracks can buckle and over-stretched electricity networks can black out.
The final report is due out in late February.