La Niña is the cold phase of the El Niño–Southern Oscillation (ENSO), characterised by stronger-than-normal trade winds in the tropical Pacific. These enhanced trades push warm surface water more forcefully westward, allowing cold, nutrient-rich water to upwell along the equatorial eastern Pacific and the coast of South America. Sea surface temperatures in the central and eastern Pacific drop 1–3 °C below normal.
La Niña events also occur every 2–7 years and can persist for 1–3 years (longer than El Niño, which typically lasts under a year). Global weather impacts roughly mirror El Niño but in reverse: enhanced rainfall in Indonesia, Australia, and the Philippines; drought in the Horn of Africa and southern South America; more active Atlantic hurricane seasons (due to reduced wind shear); and cooler-than-normal winters across the southern US. La Niña years have produced some of the most destructive Atlantic hurricane seasons on record.
For Spain and Europe, La Niña tends to favour drier winters in the Iberian Peninsula — particularly in the south and east — as Atlantic storm tracks shift northward. However, the relationship is not deterministic: other climate oscillations (the North Atlantic Oscillation, the Arctic Oscillation) modulate the signal. La Niña can also influence the frequency of cold-air outbreaks reaching western Europe. Combined with the ongoing warming trend from climate change, La Niña years still tend to be warmer globally than El Niño years from just a few decades ago — highlighting the dominant role of greenhouse gas forcing over natural variability.