La Ni帽a conditions in the eastern Pacific Ocean are expected to continue for the third winter in a row. This rare 鈥渢riple dip鈥� has contributed to extreme weather in many parts of the world, including heavy rains causing flooding in Australia and a drought in the Horn of Africa that has led to a hunger crisis.
Sea surface temperatures in the tropical Pacific have outsized influence on global atmospheric conditions. A pattern of cold temperatures in the eastern Pacific 鈥� known as La Ni帽a 鈥� is associated with a distinctive pattern of precipitation and temperature worldwide.
La Ni帽a conditions usually appear every three to five years as the eastern Pacific cycles from a warm 鈥淓l Ni帽o鈥� phase to neutral temperatures and then to the colder waters of a La Ni帽a. The cycle is driven both by winds and longer-term oscillations of the ocean.
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For the first time since 2001, existing La Ni帽a conditions are expected to continue for the third winter in a row, according to the from the World Meteorological Organization (WMO). La Ni帽a conditions developed in winter of 2020, then returned to neutral during early 2021, before appearing again that winter. A weak La Ni帽a has persisted in 2022.
The WMO update forecasts colder temperatures in the eastern Pacific through January. The forecast through March won鈥檛 be released until the end of November, but it will probably project La Ni帽a through the rest of the winter, says at the WMO. A fourth year of La Ni帽a is very unlikely 鈥� it has never since records began in the 1950s 鈥� but possible, he says.
Since 2020, the triple dip has changed weather in the regions typically affected by La Ni帽a. That includes a drying influence during parts of the year on the south-west US, East Africa and much of South America. West Africa, eastern Australia and South-East Asia have seen more precipitation.
鈥淲hat is not typical is the magnitude of these impacts,鈥� says at the WMO. He says the intensity is surprising given that the low temperatures of the current La Ni帽a are fairly mild.
In the Horn of Africa, a sequence of five below-average rainy seasons has caused major losses of crops and livestock. This, along with high prices and conflict, has created a for millions of people in parts of Somalia, Ethiopia and Kenya. Warm temperatures in the western Pacific and hotter local temperatures, both driven by climate change, have made the drought even more 鈥減unishing鈥�, says at the United States Agency for International Development.
International aid has so far averted famine conditions this year, says Verdin, but La Ni帽a continuing through the winter would signal a sixth failed rainy season. 鈥淲e should not count on the next rainy season to set things right,鈥� he says.
In Australia, intense rains have caused record flooding across the eastern part of the continent. A warmer climate, as well as cold temperatures in the eastern Indian Ocean, have also , according to the Australian Bureau of Meteorology.
Parts of North and South America have also seen drying. West Africa and Pakistan saw devastating floods earlier this year. 鈥淎ll of those bear some hallmarks of La Ni帽a,鈥� says at the National Weather Service in the US.
Is climate change behind the La Nina triple dip?
Only twice since reliable records began in the 1950s has there been a triple La Ni帽a 鈥� once in 1973-1975 and again in 1998-2001. But unlike the current La Ni帽a, both followed extreme El Ni帽o years, says L鈥橦eureux. 鈥淲hat makes this triple so interesting is that it came after very lukewarm warming.鈥�
There is no consensus on what鈥檚 driving the current triple dip. L鈥橦eureux says it could be linked to a long-term trend in Pacific surface temperature which may make La Ni帽a-like conditions more likely. Such a trend could be due to natural variability, but if so 鈥渨e鈥檙e seeing an extreme realisation of natural variability鈥�, she says.
It could also be related to human-caused climate change. Cold upwelling waters in the eastern Pacific could delay how that part of the ocean responds to warmer atmospheric temperatures, lagging behind a warmer western Pacific.
Climate models have shown warming related to human-caused climate change can affect El Ni帽o-La Ni帽a cycles. A recent found warming will make the cycle more variable as soon as 2030. But its influence on the triple dip is uncertain. 鈥淚 think we just don鈥檛 know,鈥� says L鈥橦eureux.
