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La Niña conditions have finally surfaced in the Pacific Ocean, the US-based National Oceanic and Atmospheric Administration (NOAA) declared on Thursday (January 9).
“Below average sea surface temperatures reflected along the central and eastern Pacific Ocean, thus La Niña conditions emerged in December 2024,” according to NOAA.
La Niña is a phase of what is known as the El Niño Southern Oscillation (ENSO), a climate phenomenon characterised by changes in sea temperatures along the central and eastern tropical Pacific Ocean, accompanied with fluctuations in the atmosphere overhead. ENSO influences, alters, and interferes with global atmospheric circulation, which, in turn, influences the weather worldwide.
ENSO has three phases – warm (El Niño), cool (La Niña), and neutral — which occur in irregular cycles of two to seven years. La Niña last occurred in 2020-2023, and El Niño in 2023-24.
In the neutral phase, the eastern side of the Pacific Ocean (near the northwestern coast of South America) is cooler than the western side (near the Philippines and Indonesia). This is due to the prevailing wind systems that move from east to west, sweeping the warmer surface waters towards the Indonesian coast. The relatively cooler waters from below come up to replace the displaced water.
In the El Niño phase, these wind systems weaken, leading to lesser displacement of warmer waters off the South American coast. Consequently, the eastern Pacific becomes warmer than usual. The opposite happens in the La Niña phase — the trade winds become stronger than usual, and push larger quantities of water to the western Pacific.
In India, El Niño is associated with decreased rainfall and higher temperatures, while La Niña is associated with increased rainfall and hence lower temperatures.
This La Niña event is expected to be weak and its time of emergence may not have the impact it would otherwise have had, according to meteorologists. However, it is still unclear how this “delayed” La Niña will play out given that the oceans have stayed exceptionally warmer than normal for over a year now. Experts have said that warmer ocean temperatures could have led to the delay in the sea waters to cool, that is, La Niña to emerge.
NOAA officials noted, “This La Niña will be weak and the Nino 3.4 index value is unlikely to reach -0.1 degrees Celsius during the season… ENSO events peak during winter and there is not much time for this season in the northern hemisphere”.
