The unusual combination of a strong El Niño in the Pacific Ocean and a strong shift in temperatures across the Indian Ocean could intensify heat and drought in Australia and South-East Asia, and lead to flooding in East Africa.
In May, the Pacific Ocean saw the emergence of a warm El Niño climate pattern after three years of colder La Niña conditions. The shift contributed to the unprecedented heat seen this year, although the El Niño is not expected to reach its peak strength for several months. Forecasts anticipating the potential for a “have raised alarm about impacts around the world in 2024. “There’s a lot of factors conspiring to make it a strong event,” says at the University of Colorado Boulder.
One of those factors is a shift to cold temperatures in the eastern Indian Ocean and warm temperatures in the west. This pattern is the positive phase of a cycle called the Indian Ocean Dipole (IOD). “It’s kind of like El Niño’s little brother,” says at the University of Arizona.
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Similar to an El Niño in the Pacific, a positive IOD sees trade winds push warm water to the western Indian Ocean while cold water wells up in the east, with wide-ranging impacts on the region’s climate. In early September, the Australian Bureau of Meteorology that a positive IOD was underway. It is now to continue at least until the end of the year. “This year is incredibly strong,” says DiNezio.
It is not unusual for an El Niño and a positive IOD to co-occur — about a third of positive IOD events on record are accompanied by an El Niño, says at Woods Hole Oceanographic Institution in Massachusetts. Researchers also debate the extent to which the IOD is driven by the El Niño cycle and vice versa.
But the combination of a strong El Niño and a strong positive IOD is “rare”, says at the Indian Institute of Tropical Meteorology. It hasn’t been seen since the strong El Niño of 1997 to 1998, in which the IOD was first discovered. That period cost the global economy trillions of dollars.
Both strong events at once could reinforce or cancel out each other’s influence on the global climate in complex ways. “It might be good news [in one place],” says Thirumalai. “It might be bad news somewhere else.”
Generally, both a positive IOD and El Niño are associated with hotter, drier conditions in South-East Asia and much of Australia. “If the two events co-occur it means Australia is really in for very dry and very warm temperatures,” says Ummenhofer. There could also be in Indonesia and heatwaves across South-East Asia, says Thirumalai.
Both patterns are also associated with rain in East Africa, which could lead to more extreme flooding even as the region recovers from several years of severe drought. Conversely, if it lasts far into 2024, the positive IOD could reduce the negative impact of El Niño on the Indian monsoon.
Climate change adds further uncertainty to how this event might compare with the 1997-1998 period. “A lot of the associated influences are now happening on a very much warmer planet,” says Ummenhofer. “That means any associated rainfall and drought have the potential to become more extreme.”
