El Nino labeling is changed to keep pace with a warming world

A new study links a recent rise in global monthly temperatures to a long La Nina followed by a shift toward El Nino, and NOAA this month adopted a relative tropical index to redefine when El Nino and La Nina are declared.

Scientists report that the natural El Nino–La Nina cycle is interacting with a warmer planet and helped drive a recent rise in global monthly temperatures. A new study finds that an extended three-year La Nina followed by a transition toward El Nino increased Earth's energy imbalance in 2022. Separately, the U.S. National Oceanic and Atmospheric Administration has revised how it defines El Nino and La Nina this month. NOAA now uses a relative index that compares tropical Pacific temperatures to the rest of the tropics because the baseline "normal" has shifted with warming. Key facts: - Researchers published in Nature Geoscience calculate that about three-quarters of the 2022 increase in Earth's energy imbalance can be attributed to the combination of long-term human-caused warming and the shift from a three-year La Nina to an El Nino phase. - The study authors estimate roughly 23% of the recent energy imbalance came from the prolonged La Nina, slightly more than half from greenhouse gas increases, and the remainder from other factors. - For decades meteorologists used a 30-year average updated every decade; NOAA moved to a five-year update and has now adopted a relative index to account for steadily warming tropical waters. - The new method compares temperatures to the wider tropics and has already produced differences of as much as about 0.5°C compared with the old method, a shift NOAA says is large enough to affect classifications. - NOAA forecasts an El Nino may develop in late summer or fall; the timing could influence Atlantic hurricane activity and would tend to raise global temperatures in 2027. Summary: The research links the recent multi-year temperature rise to both long-term human-caused warming and an unusually long La Nina followed by a transition toward El Nino. NOAA's revised, relative index for labeling El Nino and La Nina reflects warming tropical waters and will change how future events are counted. NOAA's forecast points to a possible El Nino later this year; the timing could influence hurricane activity and global temperatures in 2027.