El Niño and La Niña Explained: How These Climate Forces Shape Weather Worldwide
Two powerful climate phenomena are quietly driving weather patterns across the globe. Here's what El Niño and La Niña actually mean — and why they matter.
The Climate Forces Reshaping Our Weather
Deep beneath the surface of the Pacific Ocean, a natural cycle is constantly at work — one that influences rainfall, temperatures, and storm activity across nearly every corner of the planet. That cycle has two distinct phases: El Niño and La Niña. Together, they form one of the most consequential climate patterns on Earth.
According to the US science agency NOAA, La Niña conditions are currently active, with El Niño expected to emerge later in 2026.
What Is ENSO?
El Niño and La Niña are the two opposing states of a broader climate system called the El Niño Southern Oscillation, or ENSO. Though both originate in the Pacific Ocean, their influence extends far beyond it — affecting weather systems from South America to Southeast Asia and beyond.
The simplest way to distinguish between the two phases is by looking at sea surface temperatures in the tropical eastern and central Pacific Ocean. When those waters run warmer than average, El Niño is underway. When they cool below normal, La Niña takes hold.
Atmospheric pressure also plays a key role. During El Niño, pressure rises above normal near Darwin, Australia, while dropping below normal near Tahiti in the central Pacific. La Niña reverses this pattern entirely.
How Do Trade Winds Drive the Cycle?
Under neutral conditions — when neither El Niño nor La Niña is active — Pacific surface waters are naturally cooler in the east and warmer in the west. This happens because trade winds typically blow from east to west, gradually warming the water as it travels in that direction.
During El Niño, those trade winds weaken or even reverse direction, pushing warm surface water eastward across the Pacific. The result is a significant shift in where heat is concentrated at the ocean's surface.
During La Niña, the opposite occurs. Trade winds strengthen considerably, driving warm water even further west. This causes cold water to rise up from the ocean depths — a process known as upwelling — leaving the eastern Pacific cooler than usual.
A Discovery Made by Fishermen
The phenomenon was first documented not by scientists, but by Peruvian fishermen in the 1600s. They observed that unusually warm waters tended to arrive near the South American coast around December each year. In recognition of its timing, they called it "El Niño de Navidad" — Spanish for "the Christ Child."
How El Niño and La Niña Affect Global Weather
No two ENSO events are identical, and their impacts can vary considerably depending on the region and the time of year. That said, researchers have identified several consistent patterns.
Global temperatures tend to rise during El Niño and dip during La Niña. The warm water associated with El Niño sits closer to the ocean's surface and releases greater amounts of heat into the atmosphere, producing warmer and more humid air conditions. The record-breaking heat of 2024 — the hottest year ever documented — was amplified by El Niño conditions layered on top of ongoing human-driven climate change.
Regional Effects Around the World
El Niño typically brings:
- Wetter conditions to the southern United States and the Gulf of Mexico
- Drier weather across Southeast Asia, Australia, and central Africa
- A southward and eastward shift in the Pacific jet stream
- More tropical storms in the Pacific, but fewer in the Atlantic
La Niña typically brings:
- Increased rainfall across Australia, Indonesia, and equatorial South America
- Drier conditions across the southern United States
- Greater tropical storm activity in the Atlantic, including the southeastern US
What About the United Kingdom?
The impact of ENSO on the UK is more nuanced. El Niño tends to increase the likelihood of a mild winter start followed by a colder finish, while La Niña may do the reverse — raising the chances of a colder early winter giving way to milder conditions later in the season, according to the UK Met Office.
The Connection to Carbon Dioxide
Scientists have also noted a measurable rise in atmospheric CO₂ levels during El Niño events. Two factors appear to drive this trend. First, drought conditions in tropical regions slow plant growth, meaning vegetation absorbs less carbon dioxide from the atmosphere. Second, the increased frequency of wildfires — particularly across South and Southeast Asia — releases additional CO₂ into the air. Both effects compound the broader challenge of managing greenhouse gas concentrations at a time of accelerating climate change.
