El Niño

To understand El Niño and its effect on the planet, we must first look at the El Niño Southern Oscillation, also known as ENSO. This naturally occurring climate cycle is driven by interactions between the tropical Pacific Ocean and the atmosphere. It is one of the most important sources of year-to-year climate variability on Earth and has a major influence on weather patterns around the world.

ENSO has three phases:

• El Niño: Unusually warm sea surface temperatures in the central and eastern tropical Pacific.
• La Niña: Unusually cool sea surface temperatures in the same region.
• Neutral: Conditions that are neither warm enough to be El Niño nor cool enough to be La Niña.

As ENSO shifts between these phases, it changes the movement of heat, moisture and air around the planet. This can influence rainfall, drought, storms, temperatures and other weather patterns thousands of miles from the Pacific Ocean.

Find out more about ENSO from the Met Office here.

Under normal conditions, trade winds blow westward across the Pacific, pushing warm surface waters towards Southeast Asia and bringing cold, deep water up to the surface off the coast of South America.

During an El Niño, these trade winds weaken or even reverse, allowing the warm water to spread eastwards along the equator. This stops cold, deep water in the eastern Pacific from rising to the surface, causing sea surface temperatures across the central and eastern tropical Pacific to rise considerably. This shift also changes how heat is exchanged between the ocean and atmosphere, influencing weather patterns around the world.

El Niño typically occurs every two to seven years and lasts around nine to twelve months. Although a natural part of Earth's climate system, today's El Niño events are unfolding in a warmer world due to human-induced climate change, which can amplify their impacts and contribute to more extreme weather.

As one of the largest drivers of year-to-year climate variability, El Niño is closely monitored by scientists to better understand how our changing ocean influences life on Earth and to help communities prepare for the impacts ahead.

The Tropical Pacific is the engine room of much of the world’s weather. Its warm ocean waters drive a vast region of rising warm, moist air, normally centred over the western Pacific, which pumps large amounts of heat and moisture high into the atmosphere from the ocean.

During an El Niño, that warm water, along with the rising moist air, shifts thousands of kilometres east. This shift in the ocean heat source disturbs the atmosphere above, and the disturbance spreads outward like ripples on a pond, creating long-distance effects known as teleconnections. These disturbances alter the strength and position of the jet streams that adjust weather systems globally.

With the jet streams disturbed, rain, storms, and heat end up in different places than normal, with some regions getting wetter and others drier than usual.

The UK's weather is influenced more strongly by the North Atlantic and Arctic than by conditions in the tropical Pacific. As a result, El Niño's direct influence here is weaker than in many tropical regions.

However, El Niño can still have indirect effects. Scientists have identified links between El Niño and:

• Wetter and stormier periods in parts of north-west Europe
• Changes in winter weather patterns
• Disruptions to global food and commodity supply chains
• Impacts on food prices and energy markets

For the UK, some of the biggest effects may be economic rather than meteorological. Weather disruptions elsewhere in the world can affect the availability and cost of products imported into the UK.

A typical El Niño warms the central and eastern tropical Pacific by around 1-2°C above average. When temperatures exceed 2°C, scientists classify it as a "super" El Niño. Only three events in the past 50 years have reached this threshold: 1982-83, 1997-98 and 2015-16.

What makes the current event (2026) particularly notable is the intensity and speed of its development.  Scientists have observed an exceptionally rapid build-up of heat in the upper ocean, and some forecasts suggest Pacific temperatures could rival or exceed those seen during previous super El Niño events.

Three factors are attracting particular attention from scientists:

• Exceptionally rapid ocean warming
• Record amounts of heat stored in the upper ocean
• Ocean temperatures that are already elevated by long-term climate change

When a natural El Niño develops in an ocean that has already been warmed by human-induced climate change, global temperatures can temporarily reach unprecedented levels. This is why scientists often describe the current event as being 'supercharged' by climate change. El Niño does not cause climate change, but it can amplify its effects, pushing temperatures, weather extremes and ocean heat to new records.

El Niño events eventually weaken and return to neutral conditions. Some are followed by La Niña, the cooler phase of ENSO, during which cooler-than-average waters develop across parts of the tropical Pacific.

Even after an El Niño peaks, its effects can continue for many months because the atmosphere takes time to respond to changes in ocean conditions.

Scientists will continue monitoring:

• Pacific Ocean temperatures
• Trade winds
• Rainfall patterns
• Global weather impacts
• Changes to marine ecosystems

Understanding what happens next helps improve forecasts and enables better preparation for future climate risks.