The World Meteorological Organization (WMO) is studying the official declaration, in the coming weeks, of the end of the 2023-24 episode of the El Niñ - Southern Oscillation (ENSO) phenomenon. Pending the verdict of the WMO, the United States Oceanic and Atmospheric Administration (NOAA) and the Australian Bureau of Meteorology have issued reports in recent days in which they consider that this climatic episode may be over.
The WMO interim assessment on 3 March indicated that El Niño conditions (above normal temperatures in the eastern equatorial Pacific, impacting much of the planet) had weakened. However, it warned that its effects could last for months (droughts and floods in various parts of America and Asia, mainly). Thus, the change in cycle is glimpsed, and the proof is that decreases in the anomalies of warm temperatures in the Pacific are beginning to be noticed, and it is expected that they will continue in the coming months.
El Niño-Southern Oscillation episodes are part of a climate pattern that consists of variations in surface temperatures in the equatorial eastern Pacific with large-scale consequences on the planet. The weakening of the trade winds causes deep ocean waters to stop surfacing, and this causes warming over a vast ocean surface, with an impact on much of the planet. In the opposite direction, in episodes of trade winds, the waters from the bottom emerge to the surface, and this gives rise to La Niña and a cooling.
NOAA predicts a transition to ENSO-neutral conditions between April and June (85% probability), with La Niña likely to develop between June and August of this year (60% probability).
In March, sea surface temperature anomalies continued to weaken over most of the equatorial Pacific Ocean, while surface temperature anomalies were colder over the far eastern Pacific Ocean. “Taken together, the coupled ocean-atmosphere system reflected the continued weakening of El Niño,” NOAA summarizes. “Neutral conditions are expected this spring in the northern hemisphere, between April and June; and in summer, between July and August, there is a 60% chance that we will have La Niña,” corroborates Rubén del Campo, Aemet spokesperson.
El Niño and La Niña have different effects depending on geographic areas. Generally speaking, El Niño is related to an increase in temperatures, is associated with more frequent rain events in the south and southwest of the United States and is capable of causing significant droughts, for example, in the Amazon basin. The opposite phenomenon, La Niña, is associated with droughts in areas of the Horn of Africa and also in the southwest of the United States.
To what degree can El Niño be held responsible for the temperature records? “El Niño drives temperatures up. We have had monthly temperature records on a global scale for ten consecutive months. These records would not have been possible without anthropogenic climate change, which is the main factor, but this is another added factor that contributes to a greater rise in temperatures,” says Rubén del Campo. This being so, it could be expected that, with the probable arrival of La Niña, there will be a decrease in temperatures or that at least the increases will not be as spectacular and consecutive as in recent months. However, some experts fear that even with La Niña, global temperatures will continue to set record highs, solely as a consequence of climate change.
Del Campo indicates that “it is not very clear” how El Niño affects Spain. Some research points to a “certain correlation with rainier autumns and drier late winters.” But it is not a direct factor, "and many other factors intervene in the autumn and winter climate in Spain."
