The enigma of the vanished La Niña persists – and the reason remains unknown.

The predicted transition to cold La Niña conditions in the Pacific Ocean has been delayed again. Forecasters currently expect only a weak event to occur by the end of November, which is likely to limit the effect of the cooling pattern on global average temperatures.

“I don’t know why it slowed down,” he says Michelle Leroux At the National Oceanic and Atmospheric Administration (NOAA). “If someone had done it, we might have been able to predict it.”

La Niña is a cold phase of the equatorial Pacific sea surface temperature cycle known as El Niño Southern Oscillation (ENSO). Weather patterns are one of the biggest influences on the Earth’s climate, oscillating erratically between La Niña, neutral temperatures, and warm El Niño every few years.

A rare “triple bottom” La Niña event from 2020 to 2022 was replaced by a strong El Niño event in 2023. In addition to warming due to greenhouse gas emissions, this phenomenon releases heat stored in the oceans, causing average global temperatures to rise, making 2023 the hottest year on record.

As El Niño weakened in May and temperatures returned to normal, forecasters predicted a rapid transition to La Niña conditions would follow. In June, NOAA researchers issued a warning about La Niña: with a probability of over 60% The probability of onset between July and September is over 70%, and the probability of onset between August and October is over 70%. This contributed to the prediction of an extreme hurricane season in the Atlantic Ocean.

Sea surface temperatures in the Pacific Ocean have cooled since then, but a full-blown La Niña event has yet to occur, which may be contributing to the “suspiciously quiet” lull in hurricane activity. NOAA currently gives just one La Niña event. 60 percent Symptoms may occur by the end of November. The agency expects the event to be weak and short-lived, lasting from January to March.

It’s not really surprising that early bullish predictions were off the mark, he says. emily becker at the University of Miami in Florida. Forecasts made early in the year tend to be less accurate, she says, because small fluctuations in wind and water can have a big impact. It is also not unheard of for a La Niña to arrive this late, even after a strong El Niño event. Four La Niña events occurred This is the first year-end since 1950.

However, the reason for the delay is unclear. “Trade winds are moving slower than expected in parts of the eastern Pacific Ocean, which may be causing ocean temperatures near the equator to remain warmer than expected,” Rollou said. “However, this may be more of a symptom than a cause.”

Whether human-induced climate change played a role in delaying La Niña remains an open question, Becker said. Some studies suggest that climate change will make ENSO more variable, but this remains a controversial area of ​climate science. “In the last five years or so, studies have been published that say virtually everything,” Becker says.

Despite the delays, La Niña is slowly developing and is likely to have unique effects on global weather, from dry weather in the southern United States to rain in Indonesia. However, because it is a weak event, the global average temperature will not decrease as much as a strong and long-lasting event. “Although global average temperatures are falling, they are still very high,” Becker said. “We probably won’t see that much of a decline.”