Australian scientists have produced a 400-year long record of El Niño events that many thought was impossible to obtain.

The extraordinary result was teased out of coral cores, which - like tree rings - have centuries-long growth patterns and contain isotopes that can provide information about the climate of the past

Until now, coral cores had not been used to detect the different types of El Niño events.

This meant El Niño researchers were constrained by what they could say about El Niño behaviour because the instrumental record was too short and it was hard to judge whether recent decadal changes were exceptional.

The key to unlocking the El Niño record was the 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.

This was until Dr Mandy Freund took her PhD research at the University of Melbourne to a team of climate scientists and coral experts: Dr Ben Henley, Prof David Karoly, Assoc Prof Helen Mcgregor, Assoc Prof Nerilie Abram, and Dr Dietmar Dommenget.

After carefully refining the technique to reconstruct the signature of El Niño in space and time using new machine learning techniques, the scientists were able to compare recent coral results with the instrumental record.

Dr Freund found a strong agreement between the coral cores and recorded events. This confirmation allowed the team to extend the record back in time.

Dr Freund and her team found 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.

“By understanding the past, we are better equipped to understand the future, especially in the context of climate change,” said Dr Freund.

“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.”

“Prior to this research, we did not know how frequently different types of El Niño occurred in past centuries. Now we do,” said co-author Dr Ben Henley.

“This gives us an opportunity to more accurately explore how global warming may change El Niños and what this means for future weather and climate extremes.”

The study is accessible here.