Updated daily · Weekly and monthly indices from NOAA's Climate Prediction Center
El Niño and La Niña
Every few years the surface of the tropical Pacific turns unusually warm (El Niño) or unusually cool (La Niña). It is the strongest natural swing in the climate from one year to the next, and it shifts rain, drought and typhoons around the world, including near Taiwan.
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A normal year
The trade winds blow from east to west along the equator and pile warm surface water up towards Asia: the sea near Indonesia stands about half a metre higher than near South America. Off Peru, cold water rises from below. Over the warm west the air rises and brings heavy rain; over the cool east it stays dry.
El Niño
When the trade winds weaken, the warm water flows back east. The cold upwelling off Peru weakens, the eastern Pacific warms and the rainiest area moves towards the middle of the ocean. A warmer east weakens the winds further, so the change can feed on itself for months. An El Niño usually peaks between November and January and lasts about a year.
La Niña
La Niña is the opposite: stronger trade winds, more cold water rising off South America and a cool band along the equator. It often follows an El Niño and can last two or three years.
How it is measured
Scientists watch the Niño 3.4 box in the middle of the Pacific, from 5° N to 5° S and from 170° W to 120° W. NOAA counts an El Niño when the three-month average sea temperature there is at least 0.5 °C above normal for five overlapping three-month periods in a row, and a La Niña when it is at least 0.5 °C below. Above 1.5 °C is usually called strong, and above 2 °C very strong.
Effects around the world
During El Niño, Indonesia and eastern Australia tend to be drier, Peru and Ecuador wetter, and the Atlantic has fewer hurricanes. In the western Pacific, typhoons tend to form farther east, so they cross more warm water and more of them become very strong. Taiwan and southern China often have a wetter winter and spring. The whole planet warms for a while as the ocean releases heat into the air: the record warm years 2016 and 2024 both came at the end of strong El Niños.
The strongest events
Since 1950 the strongest El Niños peaked in the winters of 1982–83, 1997–98 and 2015–16, with three-month averages 2.1 °C, 2.4 °C and 2.6 °C above normal in the Niño 3.4 box. The El Niño card shows the latest numbers and the whole record since 1950.
Did you know?
Fishermen in Peru named the warm current El Niño, 'the boy', after the Christ child, because the warming of their coastal waters often arrived around Christmas.