The ocean's cooling phase: how La Niña reshapes our global weather

Science · Published 25 October 2026 Swipe more like this →

In short: When the Pacific Ocean cools, the world feels it. La Niña is a powerful climate cycle that shifts trade winds and alters atmospheric circulation. While it can temporarily dampen global warming, its local impacts—from severe droughts to flooded coastlines—create a complex web of consequences for human infrastructure and food security.

Occurring approximately every three to five years, La Niña represents the 'cool phase' within the El Niño-Southern Oscillation (ENSO) natural cycle. This climate pattern is characterised by atypical cooling of sub-surface and surface waters across the equatorial Pacific Ocean, where temperatures may decrease by 3–5 °C from the mean. This shift occurs because easterly trade winds strengthen, pushing warm surface water westward toward Asia and Australia while intensifying the upwelling of cold, nutrient-rich water off the west coast of the Americas.

These ocean dynamics have profound atmospheric consequences. The cooling pushes the jet stream northward, which typically leads to drought in the southern USA and the American Southwest, while bringing heavy rains and flooding to the Pacific Northwest and Canada. Conversely, it can increase the risk of intense rainfall in Australia and Southeast Asia. Since warm water takes up more space than denser cold water, sea levels in the eastern and central Pacific decline during La Niña periods.

While La Niña provides a temporary cooling effect on global temperatures—helping to 'keep a lid' on human-driven climate change—its impact is proportional to its strength. For example, the weak La Niña emerging in late 2025 may have less influence than stronger events. Furthermore, because oceans were slow to cool from record warmth in late 2023, global sea surface temperatures remain significantly above average even during these cooling phases. These shifts also affect marine life; increased nutrients off South America can boost stocks for fishing communities by providing more food for species like squid and salmon.

Predicting these events remains a challenge, especially when they are weak or emerge later than forecasted. While the shift to La Niña is a natural cycle, scientists continue to investigate how human-caused climate change might influence the timing and intensity of these patterns.

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