Indian Ocean phenomenon spells doom for already battered Australian climate, says study

The 2019 event cut off source for southern Australia's winter and spring rainfall, triggering extremely hot and dry conditions for the terrible fires that ravaged Australia

New changes in the Indian Ocean's surface temperatures may put Australia under increasingly hot and dry conditions, further endangering the country's already battered climate from constant bush fires in the last few months, said a new study by the Australian researchers.

Lead researcher Professor Nerilie Abram from the Research School of Earth Sciences and the Centre of Excellence for Climate Extremes at National University (ANU) said the phenomenon, known as the Indian Ocean Dipole (IOD), was a big player in the severe drought and record hot temperatures last year using coral records from the eastern equatorial Indian Ocean to reconstruct Indian Ocean Dipole variability over the last millennium.

"The 2019 event...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," said Prof. Abram, who had jointly studied the phenomenon along with other scientists from institutions in Australia, the United States, Indonesia, Taiwan and China.

Underwater coral drilling
Underwater coral drilling Jason Turl

The new research, published in Nature, first time revealed how these historically rare events have become more frequent in the 20th Century. "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," Abram said.

Co-researcher Dr Nicky Wright said, "In 1675, an event occurred that was up to 42 per cent stronger than the strongest event we have observed so far during the instrumental record, which was in 1997. The terrible impacts of this older severe events can be seen in historical documents from Asia."

1675 event

The 1675 event shows that climate extremes are possible even without human-caused climate change, said wright, upping the odds that an extreme event like this one could happen again. Co-researcher Prof Matthew England said the research also showed that a persistent, "tight coupling" has existed between the variability of the Indian Ocean Dipole and the El Niño-Southern Oscillation (ENSO) in the Pacific Ocean during the last millennium.

"Our research indicates that while Indian Ocean Dipole and El Niño events can occur independently, periods of large year-to-year swings in Indian Ocean variability also had heightened ENSO variability in the Pacific," said Prof. England from the University of New South Wales.