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What are El Niño and La Niña, and how do they change the weather? What are El Niño and La Niña, and how do they change the weather?
(2 months later)
The world has officially entered an El Niño phase, according to the US science agency NOAA. It has been confirmed that 2023 was the hottest year on record, driven by human-caused warming but also boosted by a natural weather system called El Niño.
Scientists believe the weather patterns typically seen during El Niño are likely to send global temperatures soaring to record levels in the next few years. The continuing effects of El Niño mean that 2024 could see even higher temperatures.
What is El Niño?What is El Niño?
El Niño is part of the natural climate phenomenon called the El Niño Southern Oscillation (ENSO).El Niño is part of the natural climate phenomenon called the El Niño Southern Oscillation (ENSO).
It has two opposite states - El Niño and La Niña - both of which significantly alter global weather. It has two opposite states: El Niño and La Niña, both of which significantly alter global weather.
An El Niño event is typically declared when sea surface temperatures in the tropical eastern Pacific rise to at least 0.5C above the long-term average.An El Niño event is typically declared when sea surface temperatures in the tropical eastern Pacific rise to at least 0.5C above the long-term average.
El Niño planet-warming weather phase has begunEl Niño planet-warming weather phase has begun
In normal conditions, surface water in the Pacific Ocean is cooler in the east and warmer in the west.In normal conditions, surface water in the Pacific Ocean is cooler in the east and warmer in the west.
The "trade winds" tend to blow east-to-west, and heat from the sun progressively warms the waters as they move in this direction. The "trade winds" tend to blow east-to-west, and heat from the Sun progressively warms the waters as they move in this direction.
During El Niño events, these winds weaken or reverse, sending warm surface waters eastwards instead.During El Niño events, these winds weaken or reverse, sending warm surface waters eastwards instead.
In La Niña periods, the normal east-to-west winds become stronger, pushing warmer waters further west.In La Niña periods, the normal east-to-west winds become stronger, pushing warmer waters further west.
This causes cold water to rise up - or "upwell" - from the depths of the ocean, meaning sea surface temperatures are cooler than usual in the east Pacific.This causes cold water to rise up - or "upwell" - from the depths of the ocean, meaning sea surface temperatures are cooler than usual in the east Pacific.
The phenomenon was first observed by Peruvian fisherman in the 1600s, who noticed that warm waters seemed to peak near the Americas in December.The phenomenon was first observed by Peruvian fisherman in the 1600s, who noticed that warm waters seemed to peak near the Americas in December.
They nicknamed the event "El Niño de Navidad", Christ Child in Spanish. They nicknamed it "El Niño de Navidad" - Christ Child in Spanish.
How do El Niño and La Niña change the weather?How do El Niño and La Niña change the weather?
Not every ENSO event is the same, and the consequences vary from region to region. However, scientists have observed some common effects:Not every ENSO event is the same, and the consequences vary from region to region. However, scientists have observed some common effects:
TemperaturesTemperatures
Global temperatures typically increase during an El Niño episode, and fall during La Niña.Global temperatures typically increase during an El Niño episode, and fall during La Niña.
El Niño means warmer water spreads further, and stays closer to the surface. This releases more heat into the atmosphere, creating wetter and warmer air.El Niño means warmer water spreads further, and stays closer to the surface. This releases more heat into the atmosphere, creating wetter and warmer air.
But the regional effects are complicated, and some places may be both warmer and cooler than expected at different points in the year.But the regional effects are complicated, and some places may be both warmer and cooler than expected at different points in the year.
The hottest year on record, 2016, was an El Niño year. The hottest year on record, 2023, was boosted by El Niño conditions, on top of long-term human-caused warming.
Between 2020 and 2022, the Northern Hemisphere had three La Niña episodes in a row, which stopped global temperatures from increasing as much as they otherwise would have as a result of human-caused climate change. El Niño could mean that 2024 is even hotter, the UK Met Office says, although this is far from certain.
Despite this very rare "triple dip" La Niña, the EU's climate monitoring service said that 2022 was the fifth warmest year on record. Air temperatures typically peak a few months after El Niño hits maximum strength, as heat escapes from the sea surface to the atmosphere.
Scientists warn that a return to El Niño conditions, on top of climate change, makes it almost certain that a new global temperature record will be set in the next five years. In early January 2024, El Niño was considered to be close to maximum strength, but it is expected to weaken in the coming months, according to the US science body NOAA.
How UK and Western European temperatures will respond to El Niño is complicated and uncertain. It could mean colder than average winters, for example, but that depends on how El Niño unfolds. Between 2020 and 2022, the world experienced an unusually long period of La Niña conditions, which helped keep a lid on global temperatures.
How UK and Western European temperatures respond to El Niño is complicated and uncertain. It could mean colder than average winters, for example, but that depends on how El Niño unfolds.
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Changes to rainfallChanges to rainfall
During El Niño events, the warmer water pushes the Pacific jet stream's strong air currents further to the south and the east.During El Niño events, the warmer water pushes the Pacific jet stream's strong air currents further to the south and the east.
This brings wetter weather to southern USA and the Gulf of Mexico.This brings wetter weather to southern USA and the Gulf of Mexico.
Tropical regions like southeast Asia, Australia and central Africa typically experience drier conditions.Tropical regions like southeast Asia, Australia and central Africa typically experience drier conditions.
Under La Niña, the opposite is seen. Under La Niña, the effect is reversed.
The record rainfall and flooding which Australia experienced in October 2022 was driven by La Niña.
Tropical stormsTropical storms
El Niño also affects atmospheric circulation patterns, which means there are generally more tropical storms in the tropical Pacific, but fewer in the tropical Atlantic, including the southern US.El Niño also affects atmospheric circulation patterns, which means there are generally more tropical storms in the tropical Pacific, but fewer in the tropical Atlantic, including the southern US.
During La Niña, the reverse is typically true.During La Niña, the reverse is typically true.
Carbon dioxide (CO2) levelsCarbon dioxide (CO2) levels
Scientists have also observed that CO2 levels in the atmosphere increase during El Niño events, possibly as a result of warmer and drier conditions in tropical regions.Scientists have also observed that CO2 levels in the atmosphere increase during El Niño events, possibly as a result of warmer and drier conditions in tropical regions.
If plants grow less quickly due to drought, they absorb less CO2, while more wildfires in places like South Asia mean more CO2 is released.If plants grow less quickly due to drought, they absorb less CO2, while more wildfires in places like South Asia mean more CO2 is released.
Why do these climate patterns matter?Why do these climate patterns matter?
The extreme weather events caused by El Niño and La Niña affect infrastructure, food and energy systems around the world. The extreme weather events worsened by El Niño and La Niña affect infrastructure, food and energy systems around the world.
For example, when less cold water comes to the surface off the west coast of South America during El Niño events, fewer nutrients rise from the bottom of the ocean.For example, when less cold water comes to the surface off the west coast of South America during El Niño events, fewer nutrients rise from the bottom of the ocean.
That means there is less food available for marine species like squid and salmon, in turn reducing stocks for South American fishing communities.That means there is less food available for marine species like squid and salmon, in turn reducing stocks for South American fishing communities.
Fishing stocks can be affected by the effects of El Niño
The droughts and flooding caused by the extreme 2015-16 El Niño event affected the food security of more than 60 million people, according to the UN Food and Agricultural Organisation.The droughts and flooding caused by the extreme 2015-16 El Niño event affected the food security of more than 60 million people, according to the UN Food and Agricultural Organisation.
A recent study suggested that El Niño events significantly reduce global economic growth, an effect which could intensify in the future.A recent study suggested that El Niño events significantly reduce global economic growth, an effect which could intensify in the future.
How often do El Niño and La Niña episodes happen?How often do El Niño and La Niña episodes happen?
El Niño and La Niña episodes typically occur every two to seven years, and usually last nine to 12 months.El Niño and La Niña episodes typically occur every two to seven years, and usually last nine to 12 months.
They don't necessarily alternate: La Niña events are less common than El Niño episodes.They don't necessarily alternate: La Niña events are less common than El Niño episodes.
Is climate change affecting El Niño/La Niña?Is climate change affecting El Niño/La Niña?
In 2021, the UN's climate scientists, the IPCC, said the ENSO events which have occurred since 1950 are stronger than those observed between 1850 and 1950.In 2021, the UN's climate scientists, the IPCC, said the ENSO events which have occurred since 1950 are stronger than those observed between 1850 and 1950.
But it also said that tree rings and other historical evidence show there have been variations in the frequency and strength of these episodes since the 1400s.But it also said that tree rings and other historical evidence show there have been variations in the frequency and strength of these episodes since the 1400s.
The IPCC concluded there is no clear evidence that climate change has affected these events.The IPCC concluded there is no clear evidence that climate change has affected these events.
Some climate models do suggest that El Niño events will become more frequent and more intense in future as a result of rising global temperatures - potentially leading to further warming. Some climate models suggest that El Niño events will become more frequent and more intense as a result of global warming - potentially boosting temperatures further - but this is not certain.
But scientists are not certain this will happen.
Graphics by Visual Journalism team.Graphics by Visual Journalism team.
Related TopicsRelated Topics
El NiñoEl Niño
ClimateClimate