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Indian Ocean phenomenon spells climate trouble for Australia

Fossil Porites coral (above) from the southern Mentawai Islands (Indonesia) in the eastern Indian Ocean were used to reconstruct Indian Ocean Dipole variability over previous centuries. (Photo by Nerilie Abram, Australian National University)

March 10, 2020

New international research by Woods Hole Oceanographic Institution (WHOI) and colleagues has found a marked change in the Indian Ocean’s surface temperatures that puts southeast Australia on course for increasingly hot and dry conditions.

The work led by The Australian National University (ANU) and the ARC Centre of Excellence for Climate Extremes has a silver lining, helping to improve our understanding of climate variations and the management of risk caused by Indian Ocean variability.

Lead researcher Professor Nerilie Abram said the phenomenon her team studied, known as the Indian Ocean Dipole (IOD), was a big player in the severe drought and record hot temperatures in Australia last year.

“The 2019 event, known as a positive Indian Ocean Dipole, was a big one,” said Abram from the Research School of Earth Sciences and the Centre of Excellence for Climate Extremes at ANU. “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."

“The Indian Ocean Dipole does not only affect Australian climate, but is also linked to floods in East Africa, changes in the Indian monsoon, and droughts and wildfires in Indonesia—areas that experienced unusual climate conditions during the record 2019 event”, added Caroline Ummenhofer, a WHOI climate scientist and co-author of the study.

 

WHOI physical oceanographer Caroline Ummenhofer combines temperature and current measurements from the Indian Ocean with climate records and computer simulations to understand how ocean patterns influence rainfall and extreme weather events on adjacent landmasses. (Photo by Tom Kleindinst, © Woods Hole Oceanographic Institution)

The new research published in Nature reveals that these historically rare events have become much more frequent and intense during the 20th Century, and this situation is expected to worsen if greenhouse gas emissions continue to rise. The research team, which involved scientists from institutions in Australia, the United States, Indonesia, Taiwan and China, used coral records from the eastern equatorial Indian Ocean to reconstruct Indian Ocean Dipole variability over the last millennium with unprecedented precision.

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

The research highlighted that the Indian Ocean can harbour events that are even stronger than the extreme conditions seen in 2019. In 1675, an event occurred that was up to 42 percent stronger than the strongest event observed so far during the instrumental record, which was in 1997. The dire impacts of this older severe event can be seen in historical documents from Asia.

“Having this new extended information of Indian Ocean Dipole events recorded by corals going back centuries is particularly valuable, as few long-term observations exist from the Indian Ocean,” said Ummenhofer. “These new records help us understand how the Indian Ocean interacts with ENSO in the Pacific and can ultimately benefit Indian Ocean rim countries be better prepared for future climate risks.”

This research was supported by the National Science Foundation and the Australian Research Centre of Excellence for Climate Extremes.

The Woods Hole Oceanographic Institution is a private, non-profit organization on Cape Cod, Mass., dedicated to marine research, engineering, and higher education. Established in 1930 on a recommendation from the National Academy of Sciences, its primary mission is to understand the ocean and its interaction with the Earth as a whole, and to communicate a basic understanding of the ocean’s role in the changing global environment. For more information, please visit www.whoi.edu.