This research will help in predicting further trends towards extreme weather in the future and plan better
El Niños have become stronger and their pattern too has been changing, the world’s first 400-year-long seasonal record of El Niño created by Australian scientists has revealed.
While a new type of El Niño has become far more prevalent in the last three decades than at any time in the past four centuries in the Central Pacific, the traditional El Niño events have also become more intense in nature.
The four-centuries-long record published in the journal Nature Geoscience opens a door not just to past changes but those to El Niños in the future as well, say the scientists who worked on project for three years.
The research team includes Mandy Freund, who led the project, and a team of climate scientists and coral experts namely Ben Henley, David Karoly, Helen McGregor, Nerilie Abram, and Dietmar Dommenget.
The El Niño trends of the past have been studied on the basis of coral cores spanning the Pacific Ocean, as part of Freund's PhD research at the University of Melbourne and the Centre of Excellence for Climate Extremes.
It was made possible because coral cores — like tree rings — have centuries-long growth patterns and contain isotopes that can tell us a lot about the climate of the past. Hence, the key to unlocking the El Niño record was understanding that coral records contained enough information to identify seasonal changes in the tropical Pacific Ocean.
However, using coral records to reconstruct El Niño history at a seasonal timescale had never been done before and many people working in the field considered it impossible.
Predicting extreme weathers to plan better
El Niños are linked to extreme weather across the globe, with particularly profound effects on precipitation and temperature extremes in Australia, South East Asia and the Americas. Hence, the study is expected to strengthen the science of predicting extreme weathers and plan better.
"Having a better understanding of how different types of El Niños have affected us in the past and present will mean we are more able to model, predict and plan for future El Niños and their wide-ranging impacts," said Freund.
The trend of El Niño in the last four centuries shows a variation in El Niño types. There has been a simultaneous increase in central Pacific events and a decrease in eastern Pacific ones since the late twentieth century.
This leads to a ratio of central to eastern Pacific events that is unusual in a multi-century context. Compared to the past four centuries, the most recent 30-year period includes fewer, but more intense, eastern Pacific El Niño events.
There has been an unprecedented increase in the number of El Niños forming in the central Pacific over the past 30 years, compared to all 30-year periods in the past 400 years. At the same time, the stronger eastern Pacific El Niños were the most intense El Niño events ever recorded, according to both, the 100-year-long instrumental record and the 400-year-long coral record.
According to Freund, the occurrences of more El Niños forming in the central Pacific Ocean in recent decades is unusual across the past 400 years. The trend also shows that stronger Eastern Pacific El Niños, like those that occurred in 1997-98 and 2015-16 may be growing in intensity.
According to the latest World Meteorological Organization forecasts, weak El Niño conditions have developed over the equatorial Pacific Ocean and they are likely to persist this summer.
The India Meteorological Department (IMD) too takes El Niño into account for forecasting the monsoon and El Niño years usually mean a weak monsoon and more episodes of heat waves in India. In fact, IMD in its monsoon forecast on April 15, 2019 has predicted weak El Niño conditions during the monsoon season, with reduced intensity in the later part of the season. It has also projected near normal monsoon this year. But Skymet Weather has predicted a slow start to the monsoon because of El Niño.
An understanding of El Niños in the past and present based on this four-century-old trend needs to be explored further by India for modelling, predicting and planning for future El Niños and their wide-ranging impacts.
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