EL NIÑO RECLASSIFICATION

NEWS: Scientists have updated the classification criteria for El Niño and La Niña as rapid global warming alters ocean temperature baselines

KEY DATA

• Oceanic Niño Index (ONI): NOAA-tracks ENSO using the ONI based on east-central equatorial Pacific SST deviationsà modified how anomalies are calculated to filter out global warming effects.
• Baseline Method Shift: NOAA now uses a rolling 30-year baseline updated every 5 years, making the reference period non-stationary.
• The revised rolling baseline: subtracts the long-term warming trend, enabling a clearer distinction between natural ENSO variability and anthropogenic climate change signals

Need for Changing the Labelling Criteria

• Baseline Warming Shift: Rising global sea surface temperatures have altered historical reference baselines, requiring recalibration of El Niño–La Niña thresholds.
• A recent study attributes: Nearly 75% of the surge in Earth’s energy imbalance to the combined effect of anthropogenic warming and ENSO phase transition.
• Triple-Dip La Niña Effect: The unusual 2020–2023 triple-dip La Niña suppressed surface heat release, followed by a sharp warming spike.