Scientists update El Niño, La Niña classification system amid global warming

For decades, meteorologists relied on the Oceanic Niño Index (ONI), which measures sea surface temperatures in the Niño 3.4 region of the tropical Pacific against a 30-year average. A rise of 0.5 degrees Celsius above that baseline signaled El Niño, while a drop of 0.5 degrees indicated La Niña.

However, as climate change has warmed the entire tropical Pacific, defining what is “normal” has become more complicated. Because overall ocean temperatures are rising, the historical 30-year average can lag behind current conditions. This reduces the contrast that typically signals the start of these climate cycles and makes the old method less precise in real time.

In response, the U.S. National Oceanic and Atmospheric Administration (NOAA) introduced a new tool this month called the Relative Oceanic Niño Index (RONI). Instead of comparing temperatures only to a fixed historical baseline, the new index measures how the Niño 3.4 region differs from the rest of the tropical oceans at the same time.

The agency added that ONI depends heavily on a 30-year reference period, which makes the approach outdated as ocean temperatures shift.

Earlier, Qazinform reported that a separate study found a sharp global increase in extreme day-to-day temperature swings.