What are El Niño and La Niña and how do they change the weather?

Rescuers in flood waters in Melbourne, Australia in October 2022

Australia experienced severe flooding in October 2022

Global temperatures and rainfall are influenced by a climatic phenomenon called the El Niño Southern Oscillation (ENSO) system.

It has two opposing states – El Niño and La Niña – that significantly change the weather around the world.

What happens during these events?

For several years, there have been successive La Niña periods in the world, which have lowered temperatures and brought heavy rains to Canada and Australia.

Winds blowing along the equator over the Pacific Ocean – from South America in the east to Asia in the west – were stronger than usual.

These trade winds pile up warm water off the coast of Asia, raising sea levels. In the east, near the Americas, cold water flows up to the surface.

Infographic showing how, under La Niña conditions, warmer ocean surface waters are further west than usual in an area of ​​the Pacific Ocean stretching from Australia and Papua New Guinea to the west coast of South and Central America.

During La Niña conditions, warmer water concentrates to the west around Asia, pushing more cold water to the east

During an El Niño, the opposite happens – weaker trade winds mean warm water is spreading back towards the Americas and less cold water is rising towards the surface.

This phenomenon was first observed by Peruvian fishermen in the 17th century.

They noticed that in December the warm waters seemed to peak near the Americas, and nicknamed it “El Niño de Navidad,” Spanish for Baby Jesus.

Infographic showing how, during El Niño conditions, warmer ocean surface waters are further east than usual in an area of ​​the Pacific Ocean stretching from Australia and Papua New Guinea to the west coast of South and Central America.

During an El Niño, the warmer surface waters of the oceans are further east than usual

How do El Niño and La Niña affect our weather?

Not every El Niño or La Niña event is the same, but scientists have observed some common effects:

temperatures

Global temperatures rise by about 0.2°C during an El Niño episode and fall by about 0.2°C during a La Niña.

This is because El Niño means warmer water spreads further and stays closer to the surface.

This releases more heat into the atmosphere, creating moister and warmer air.

The hottest year on record, 2016, was the year of El Niño.

Between 2020 and 2022, there were three La Niña episodes in a row in the northern hemisphere.

Despite the triple La Niña, data from the EU’s climate monitoring service on Tuesday showed that 2022 was the world’s fifth-warmest year.

Prof. Adam Scaife of the Met Office said: “The average global temperature over the past three years has been near record highs, but would have been even higher were it not for the cooling effects of an extended La Niña.”

A temperature increase of 0.2°C would add about 20% to the existing global temperature increase due to climate change.

He added that the Met Office expects La Niña to end later this year, “raising the prospect of even higher global temperatures”.

December 2022 Pacific Ocean sea surface temperature anomaly map, showing La Niña in progress with lower than normal surface temperatures

December 2022 map of the Pacific Ocean, showing La Niña in progress with cooler than normal surface temperatures

Changes in precipitation

During El Niño events, warmer water pushes the Pacific Jet Stream’s strong air currents further south and east across the Americas.

This results in wetter weather in the southern US and the Gulf of Mexico, while areas in the northern US and Canada can be drier.

Asia, Australia, and Central and Southern Africa tend to experience drought.

In the case of La Niña, the situation is the opposite: drought in the southern United States and heavy rains in Canada and Asia.

In October 2022, Australia experienced record rainfall and flooding from La Niña.

A skeleton of a fish can be seen in the Navarro lagoon

Laguna Navarro in Buenos Aires, Argentina, dried up due to the December drought

Tropical storms

La Niña also generates more hurricanes in the Atlantic – affecting Florida and other southern US states – but fewer tropical storms in the Pacific.

El Niño is different.

How often do these episodes happen?

El Niño and La Niña episodes occur on average every two to seven years and typically last nine to 12 months.

They do not necessarily alternate: La Niña events are less common than El Niño episodes.

How do these events affect us?

Extreme weather events caused by El Niño and La Niña affect infrastructure, food and energy systems around the world.

According to the Food and Agriculture Organization of the United Nations, the 2014-16 El Niño event caused drought in Canada and Asia, causing crop failures and threatening the food security of more than 60 million people.

During an El Niño, less cold water comes to the surface off the coast of the Americas, which would bring nutrients from the ocean floor.

This means less food is available for marine species such as squid and salmon, which in turn reduces the fish stocks of South American fishing communities.

Does climate change affect this phenomenon?

In 2021, UN climatologists, the IPCC, stated that the ENSO events that have occurred since 1950 are stronger than those seen between 1850 and 1950.

However, it has also been found that historical evidence such as tree rings, coral and sediment records indicate that there have been variations in the frequency and severity of these episodes since the 15th century.

The IPCC concluded that there is no conclusive evidence that climate change has influenced El Niño or La Niña phenomena.

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