In early 2026, the Climate Prediction Center (CPC) officially adopted the “Relative Niño 3.4 Index” as its primary metric for tracking ENSO (El Niño/La Niña). Unlike the old index, which looked at absolute temperatures, the “Relative” index compares the Niño region to the rest of the global tropics, accounting for the fact that the entire ocean is warming due to climate change.
Because the entire planet is warming, the “average” temperature of the ocean is much higher than it was in 1950. This meant that the old index was “permanently” in El Niño territory, making it useless for predicting weather shifts. Professionals search for “RONI (Relative ONI) transition tables” to convert their historical climate records into this new, more accurate format.
The weather impacts of El Niño are driven by the difference in temperature between the Pacific and the surrounding oceans. By focusing on the “Relative” difference, the new index correctly identifies when the Pacific is truly “acting” like an El Niño, leading to much better 3–6 month forecasts for rain in California or snow in the Northeast. Pros search for “RONI skill scores” to see if this change has fixed the “failed” forecasts of 2024–2025.
To keep up with climate change, the CPC used to update its “average” every five years. The Relative Index eliminates the need for these confusing “jumps” in data. Industry pros search for “RONI vs. ERSST.v6” to understand how the latest sea-surface temperature datasets are being used to calculate this relative value in real-time, providing a smoother, more scientifically robust climate signal.