New Index Replaces Traditional ONI to Counter Warming Bias The Relative Oceanic Niño Index (RONI) was officially adopted on 17 February 2026, supplanting the long‑used Oceanic Niño Index (ONI) because rapid tropical‑Pacific warming was obscuring true El Niño temperature spikes [1]. Researchers argue that the old metric’s reliance on a static 30‑year baseline could no longer distinguish climate‑change trends from genuine El Niño events [1]. The shift aims to restore reliable detection of El Niño strength for climate monitoring and disaster preparedness [1].

RONI Calculates Strength by Subtracting Basin‑Wide Anomalies RONI determines El Niño intensity by first measuring temperature anomalies in the Niño 3.4 region, then subtracting the average anomalies across the entire tropical Pacific basin [1]. This subtraction removes the warming “background” introduced by global climate change, producing a clearer signal of the event itself [1]. The refined calculation enables forecasters to issue earlier warnings with higher confidence [1].

Forecasters Expect More Accurate Damage Estimates and Hurricane Predictions Accurate El Niño/La Niña forecasts are critical because the phenomena influence floods, droughts, and the Atlantic hurricane season, with economic impacts measured in billions of dollars [1]. NOAA forecaster Michelle L’Heureux praised RONI for “better capturing the interactions between the ocean and atmosphere,” calling the previous method “blurry glasses” [1]. The improved index is projected to reduce mis‑allocation of resources and mitigate financial losses worldwide [1].

Researchers Attribute ONI Failure to Decade‑Long Ocean Warming Emily Becker of the University of Miami noted that over the past ten years the traditional ONI fell out of sync with observed climate impacts as global oceans warmed faster than the index could accommodate [1]. She highlighted that RONI’s baseline correction directly addresses this mismatch, restoring alignment between index readings and real‑world weather outcomes [1]. The scientific community views the change as a necessary adaptation to a warming planet [1].