The unusual combination of a strong El Ni帽o 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 Ni帽o climate pattern after three years of colder La Ni帽a conditions. The shift contributed to the unprecedented heat seen this year, although the El Ni帽o is not expected to reach its peak strength for several months. Forecasts anticipating the potential for a 鈥渉ave raised alarm about impacts around the world in 2024. 鈥淭here鈥檚 a lot of factors conspiring to make it a strong event,鈥� 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). 鈥淚t鈥檚 kind of like El Ni帽o鈥檚 little brother,鈥� says at the University of Arizona.
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Similar to an El Ni帽o 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鈥檚 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. 鈥淭his year is incredibly strong,鈥� says DiNezio.
It is not unusual for an El Ni帽o and a positive IOD to co-occur 鈥� about a third of positive IOD events on record are accompanied by an El Ni帽o, says at Woods Hole Oceanographic Institution in Massachusetts. Researchers also debate the extent to which the IOD is driven by the El Ni帽o cycle and vice versa.
But the combination of a strong El Ni帽o and a strong positive IOD is 鈥渞are鈥�, says at the Indian Institute of Tropical Meteorology. It hasn鈥檛 been seen since the strong El Ni帽o 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鈥檚 influence on the global climate in complex ways. 鈥淚t might be good news [in one place],鈥� says Thirumalai. 鈥淚t might be bad news somewhere else.鈥�
Generally, both a positive IOD and El Ni帽o are associated with hotter, drier conditions in South-East Asia and much of Australia. 鈥淚f the two events co-occur it means Australia is really in for very dry and very warm temperatures,鈥� 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 Ni帽o on the Indian monsoon.
Climate change adds further uncertainty to how this event might compare with the 1997-1998 period. 鈥淎 lot of the associated influences are now happening on a very much warmer planet,鈥� says Ummenhofer. 鈥淭hat means any associated rainfall and drought have the potential to become more extreme.鈥�
