The rare event behind our crazy weather
A rare, intense Indian Ocean Dipole - the Indian Ocean version of the Pacific El Nino phenomenon - was a significant factor in Australia's drought and bushfire crisis and could become more frequent, new research has found.
"The 2019 event, known as a positive Indian Ocean Dipole (where the west ocean warms in comparison to the east) was a big one," Australian National University Research School of Earth Sciences lead researcher Professor Nerilie Abram said.
"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," Prof Abram said.
An international team, assessing coral skeletons and growth in the Indian Ocean to track temperature back 780 years, found a positive dipole in 1997, which contributed to Australia's millennium drought, and again in 2019, were the most extreme examples since an event in 1675 which took place during the "Little Ice Age" that devastated south-Central Asia.
"Historically, strong events like the one we saw in 2019 have been very rare. 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."
Prof Abram said while the pre-industrial age 1675 event was 30-40 per cent more extreme than dipoles in 1997 and 2019, pronounced changes were becoming more frequent in recent decades.
On current projections, extreme dipoles will occur three times more frequently this century than last but if the international community met the Paris 2030 climate targets it would reduce to twice the frequency.
"The more ambitious our action to reduce greenhouse gases the lower the future risk will be."
While Indian Ocean Dipole and Pacific El Nino can occur independently, the Indian temperature swings can magnify El Nino - Southern Oscillation (ENSO) which impacts Australia from the east, the analysis found.
ANU co-researcher Dr Nicky Wright said the 1675 event showed the extremes possible without human-cause climate change.
"By causing positive Indian Ocean Dipole events to become stronger and more common, we are now upping the odds that an extreme event like this one could happen again," Dr Wright said.
The research, by institutions in Australia, the US, Indonesia, Taiwan and China has been published in the journal Nature.