El Niño and La Niña are natural climate patterns that dramatically influence global weather, and they’re about to shift again. While La Niña is currently in effect, scientists predict an El Niño development later in 2026. These aren’t just regional phenomena; they reshape temperatures and rainfall worldwide.
What Exactly Are El Niño and La Niña?
These events are opposite phases of the El Niño-Southern Oscillation (ENSO), a recurring climate pattern centered in the Pacific Ocean. The key difference lies in sea surface temperatures: El Niño brings warmer waters, while La Niña cools them.
This isn’t just about temperature. ENSO also alters atmospheric pressure; El Niño sees high pressure near Australia and low pressure near French Polynesia, with the reverse during La Niña. In neutral conditions, the Pacific maintains a typical temperature gradient—cooler in the east, warmer in the west.
The cycle works like this: normal trade winds push warm surface water westward, heating it along the way. El Niño weakens these winds, allowing warm water to surge eastwards. La Niña strengthens the winds, driving warm water further west and causing cold water to upwell from the depths.
The pattern was first noted centuries ago by Peruvian fishermen, who observed warm waters peaking around Christmas and dubbed it “El Niño de Navidad” (the Christ Child).
How Do These Shifts Affect Global Weather?
The effects are complex, but some trends are clear:
- Temperatures: El Niño generally boosts global temperatures, while La Niña has a cooling effect. However, regional impacts are highly variable. 2024, the hottest year on record, was partially driven by El Niño alongside long-term climate change.
- Rainfall: El Niño tends to bring wetter conditions to the southern US and drier conditions to Southeast Asia and Australia. La Niña reverses this pattern, favoring rainfall in Australia and Indonesia while drying out the southern US.
- Tropical Storms: El Niño often increases storms in the Pacific, but reduces them in the Atlantic. La Niña has the opposite effect.
- CO2 Levels: El Niño events can lead to higher atmospheric CO2 levels due to reduced plant growth in drought-stricken regions and increased wildfires.
The UK’s weather is also affected, with El Niño potentially increasing the chance of a mild winter start followed by a cold end, and La Niña increasing the chances of a cold start and mild end.
Why Do These Patterns Matter?
These extreme weather events disrupt infrastructure, food supplies, and energy systems globally. For example, El Niño reduces nutrient upwelling off the South American coast, impacting marine life and fisheries. The 2015-16 El Niño event left over 60 million people food insecure, according to the UN.
Episodes typically occur every 2-7 years, with the current La Niña beginning in mid-to-late 2024.
The Role of Climate Change
The IPCC currently finds no conclusive evidence that climate change has altered the frequency or intensity of El Niño/La Niña events. However, some climate models suggest that warming could lead to more frequent and severe oscillations between the two phases. This remains an area of active research.
Understanding ENSO is critical not just for forecasting weather but for preparing for its cascading effects on global systems. As climate change continues, monitoring and predicting these shifts will become even more vital.
