El Niño says goodbye and La Niña threatens to dominate the global climate

After a year of dominance, El Niño released its grip on the tropical Pacific in May 2024, according to the latest update from the National Oceanic and Atmospheric Administration (NOAA), a United States government agency. El Niño, the warm phase of the El Niño Southern Oscillation (ENSO), is the largest natural source of annual variations in our planet's seasonal climate. Since May 2023, this phenomenon has disrupted the climate in the tropics, contributing to record ocean temperatures, drought in the Amazon and Central America, extreme precipitation in southern Brazil and several other situations.

With El Niño now on the wane, many had hoped for a period of climate neutrality, but NOAA warns there won't be much time to rest. The climate of the tropical Pacific appears to be swinging towards its other extreme: La Niña. In the Pacific, La Niña brings below-average temperatures in the central-eastern part of the ocean, stronger winds both at the surface and at high altitudes, and more intense rains over Indonesia and the rest of the maritime archipelago. The forecast team believes there is a 65% chance that La Niña will establish itself between July and September.

Expected impacts and predictions

The transition to La Niña could influence the peak of the Atlantic hurricane season. Even if the transition occurs more slowly, the chances of La Niña being present by the Northern Hemisphere winter are 85%, similar to NOAA's prediction in previous months. Given this probability, it is prudent to remember the typical impacts of La Niña on temperatures and precipitation in the US.

By early April, the atmospheric part of El Niño—weak or absent east-west trade winds across the tropical Pacific, dryness over Indonesia, strong convection, and rain east of the International Date Line—had largely ceased. However, surface water temperatures in the central-eastern Pacific were still more than a degree Celsius above the long-term average. Without the atmosphere reinforcing these warm anomalies, surface temperatures cooled significantly in April and May. Stronger trade winds have already begun to cool superheated surface waters.

The strength of La Niña

Historically, the direct transition from a strong El Niño to a strong La Niña is rare. Only ten times in historical records has ENSO switched from El Niño to La Niña in one year, without a neutral winter period. Although four of the six strong El Niños evolved into strong La Niñas, the relationship between the strength of an El Niño and the subsequent strength of a La Niña is unclear.

The strength of the next La Niña will become more evident in the coming months, but it is important to remember that even moderate or weak La Niña events can have significant impacts in certain regions. Therefore, with the high probability (85%) of a winter influenced by La Niña, it is crucial to pay attention to the known impacts of the phenomenon.