New research has found a weather phenomenon that helped cause the recent horror bushfire season is becoming more frequent and more severe.

An extremely strong positive Indian Ocean Dipole (IOD) contributed to dry and warm conditions at the start of the year, which helped fan flames across eastern Australia, causing insured losses of $2 billion.

Research led by the Australian National University and the ARC Centre of Excellence for Climate Extremes warns that positive IODs are becoming increasingly common as Australia’s climate changes.

Lead researcher Professor Nerilie Abram says last year’s positive IOD was “a big one”.

“It cut off one of the major sources for southern Australia's winter and spring rainfall, and set up the extremely hot and dry conditions for the terrible fires that ravaged Australia this summer,” she said.

The research, published in the journal Nature, says these historically rare events became much more frequent and intense during the 20th Century – a situation that is expected to worsen if greenhouse gas emissions continue to rise.

The research team, which involved scientists from Australia, the US, Indonesia, Taiwan and China, used coral records from the eastern equatorial Indian Ocean to reconstruct IOD variability over the past millennium with unprecedented precision.

“Historically, strong events like the one we saw in 2019 have been very rare,” Professor Abram said.

“Over the reconstruction beginning in the year 1240, we see only 10 of these events, but four of those have occurred in just the last 60 years.”

Co-researcher Nicky Wright says the research shows even stronger events are possible.

“In 1675, an event occurred that was up to 42% stronger than the strongest event we have observed so far during the instrumental record, which was in 1997,” Dr Wright said.

“By causing positive IOD events to become stronger and more common, we are now upping the odds that an extreme event like this one could happen again.”