The Mystery of the Delayed La Niña: Scientists Search for Answers

“We don’t know why it’s slowing down,” admits Michelle L’Heureux of the U.S. National Oceanic and Atmospheric Administration (NOAA). “If we did, we might have predicted this more accurately.”

This unusual shift is stirring concern within the scientific community, as La Niña plays a crucial role in regulating weather patterns globally. It is part of the El Niño-Southern Oscillation (ENSO) system, which fluctuates irregularly between La Niña’s cooling, neutral phases, and El Niño’s warming every few years.

A rare “triple-dip” La Niña that persisted from 2020 to 2022 gave way to a powerful El Niño in 2023. Combined with the effects of human-caused climate change, the ocean’s release of stored heat contributed to 2023 being recorded as the hottest year ever.

After El Niño subsided, neutral conditions dominated the Pacific by May, and experts expected a quick shift to La Niña over the summer. In June, NOAA projected a 60% chance of La Niña forming between July and September, increasing to over 70% between August and October. This prediction also heightened expectations for an intense Atlantic hurricane season.

However, although Pacific waters have cooled somewhat, the anticipated La Niña has not fully developed. This delay may help explain the relatively quiet hurricane season so far. NOAA now estimates only a 60% chance of La Niña emerging by November’s end, and if it does appear, it is likely to be weak and brief, lasting only through the early months of 2024.

The missed forecast does not surprise Emily Becker from the University of Miami, who notes that early-year climate predictions are notoriously tricky. Even minor shifts in wind or water patterns can create unexpected outcomes, she explains. While late-emerging La Niñas following strong El Niño events are uncommon, they are not unprecedented — four similar cases have occurred since 1950.

Scientists remain unsure about what caused this particular delay. “We have seen weaker-than-expected trade winds in parts of the eastern Pacific, which could be preventing the equator’s surface waters from cooling as predicted,” says L’Heureux. “But it’s unclear if this is the main cause or just another symptom.”

Whether human-driven climate change has influenced this delayed La Niña remains uncertain. Becker notes that research on climate change’s impact on ENSO patterns offers mixed conclusions. Some studies suggest climate change could increase ENSO variability, but the topic remains heavily debated. “Recent studies are all over the place,” she says.

Despite the delay, La Niña conditions are slowly setting in and will likely affect global weather patterns, bringing dry spells to the southern U.S. and increased rainfall in Indonesia. However, since it will likely be a weak event, its cooling effect on global temperatures will be limited. “We’ve seen some cooling in global averages, but they are still exceptionally high,” Becker adds. “The temperature drop probably won’t be as significant as it would with a stronger La Niña.”