Weather conditions for bushfires like the Black Summer have occurred seven times in the past 2000 years, new research shows.
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The periods in which these conditions occurred were the 1980s and the Middle Ages from 1243 to 1247, 1233 to 1234, 1229 to 1231, 1193 to 1195 and 1173 to 1176.
They also occurred during the Byzantine era from 486 to 496.
The research, which involved University of Newcastle Associate Professor Anthony Kiem, will be released on Friday.
The team studied sea salt in ancient ice cores in Antarctica, which revealed that Australia could be seriously underestimating bushfire risk.
The researchers said multiple factors aligned to cause the Black Summer - drought, natural climate variability and human-caused climate change.
They warned that these conditions will align again and there was an "urgent need" to prepare.
The study's lead author, UNSW's Dr Danielle Udy, said "buried in the ice is a warning".
"This isn't just a future risk. We need to plan for bushfire seasons worse than the Black Summer," Dr Udy said.
Dr Kiem, a co-author, said "bushfire planning is based on observations - the observed record".
"Our bushfire weather observations only extend back to 1950.
"The assumption was that something like the Black Summer was impossible or a very big outlier."
He said the study showed that "it's possible to have bushfires as bad or worse than the Black Summer due to natural variability alone".
"But then you add climate change on top and the risk is exponentially greater. That on its own means we're underestimating things."
The study noted that the severity and frequency of past fires was influenced by vegetation type, fuel loads and land management decisions.
"The disruption of Indigenous cultural burning practices in Australia following colonial settlement has been argued to have increased shrub cover," it said.
"This may have exacerbated the intensity of the Black Summer fires beyond expectations from climate variability and change alone."
Dr Kiem said the Black Summer "exposed how flawed the planning and management of bushfires are".
"It was unprecedented in the observational record. Because of that it wasn't considered in the planning," he said.
"What our study showed was that just because it's unprecedented in the 60-odd years we have records for, doesn't mean it's not possible.
"Seven times over the last 2000 years we've had conditions as bad or worse than the Black Summer. Some were worse in terms of the intensity of the wind and heat."
The size of weather systems that cause extreme bushfire weather in Australia are so big, they can affect Antarctica at the same time.
This "weather bridge" between the two continents is preserved in the ice core record as changes in sea salt concentration.
The study's co-author Dr Tessa Vance, of the Australian Antarctic Program Partnership, said the ice cores were drilled at Law Dome camp.
That's a place where ancient snow is compressed in the ice.
Dr Vance said this had provided "valuable datasets of past climate that enable us to put recent extreme events into context".
