El Ninos are becoming more common in the central Pacific but also developing into more extreme events in the ocean's east.

Mandy Freund, a post-doctorate researcher at the CSIRO and lead author of the paper published on Tuesday in Nature Geoscience, identified the shift using coral cores that plot El Nino events back to 1600.

El Ninos that formed in the eastern equatorial Pacific are becoming relatively rare, compared with those in the central Pacific. The 1997-98 and 2015-16 events, though, were two of the most powerful on record. Credit:NASA

"Corals are really an amazing archive," said Dr Freund, who based her PhD at Melbourne University on the study. "They give you such precise information - I wondered why nobody had tried them before."

Oxygen isotopes and the ratio of strontium and calcium within the coral - drawn from 24 locations - allowed researchers to recreate past seasonal locations and strengths of El Ninos even in remote regions.