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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?
(10 days later)
Australia experienced severe flooding in October 2022 as a result of La Niña The world has officially entered an El Niño phase, according to the US science agency NOAA.
New data shows that 2022 was the fifth hottest year for Europe since records began. 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.
But scientists are warning that 2023 could be even warmer, as a climate phenomenon called La Niña - which has been suppressing global temperatures - comes to an end. What is El Niño?
What is La Niña? El Niño is part of a the natural climate phenomenon called the El Niño Southern Oscillation (ENSO).
La Niña is part of a climate phenomenon called the El Niño Southern Oscillation (ENSO) system. 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 weather patterns across the globe. 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.
For the last few years, the world has been in successive La Niña periods, which have lowered temperatures and brought heavy rains to Canada and Australia. El Niño planet-warming weather phase has begun
Winds blowing along the Equator above the Pacific Ocean - from South America in the east towards Asia in the west - were stronger than normal. In normal conditions, surface water in the Pacific Ocean is cooler in the east and warmer in the west.
These "trade winds" piled warm water off the coast of Asia, raising the sea surface level. In the east, near the Americas, cold water flowed upwards to the surface. 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 the opposite happens - weaker trade winds mean the warm water spreads out back towards the Americas, and less cold water rises towards the surface. During El Niño events, these winds weaken or reverse, sending warm surface waters eastwards instead.
The phenomenon was first observed by Peruvian fisherman back in the 1600s. In La Niña periods, the normal east-to-west winds become stronger, pushing warmer waters further west.
They noticed that warm waters seemed to peak near the Americas in December, and nicknamed the event "El Niño de Navidad", Christ Child in Spanish. 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.
They nicknamed the event "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 El Niño or La Niña event is the same, but scientists have observed some typical 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 increase by about 0.2C during an El Niño episode, and fall about 0.2C 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.
The hottest year on record, 2016, was an El Niño year.The hottest year on record, 2016, was an El Niño year.
Between 2020 and 2022, the northern Hemisphere had three La Niña episodes in a row. 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.
Despite the La Niña triple, the EU's climate monitoring service says that 2022 was the fifth warmest year on record. Despite this very rare "triple dip" La Niña, the EU's climate monitoring service said that 2022 was the fifth warmest year on record.
Prof Adam Scaife from the Met Office said: "Global average temperature over the last three years has been at near record levels, but it would have been even higher without the cooling effects of a prolonged La Niña." 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.
A 0.2C temperature rise would add about 20% to the existing global temperature rise from climate change. 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.
The Met Office expects La Niña to end later this year, "raising the prospect of even higher global temperatures".
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Map of the Pacific Ocean from December 2022, showing La Niña is underway with cooler than usual surface temperatures Unexplained ocean warming alarms scientists
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 US states and the Gulf of Mexico, while the north of the US and Canada remain drier. This brings wetter weather to southern USA and the Gulf of Mexico.
Asia, Australia and Central and Southern Africa typically experience drought. Tropical regions like southeast Asia, Australia and central Africa typically experience drier conditions.
In La Niña events the opposite is seen: drought in the southern US, and heavy rains in Canada and Asia. Under La Niña, the opposite is seen.
In October 2022, Australia experienced record rainfall and flooding driven by La Niña. The record rainfall and flooding which Australia experienced in October 2022 was driven by La Niña.
The Navarro lagoon in Buenos Aires, Argentina, dried up due to drought in December
Tropical stormsTropical storms
La Niña also generates more hurricanes in the Atlantic - affecting Florida and other southern states of the US - but fewer tropical storms in the Pacific. 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.
The opposite is true of El Niño events. During La Niña, the reverse is typically true.
How often do these episodes happen? Carbon 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.
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?
The extreme weather events caused 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.
That means there is less food available for marine species like squid and salmon, in turn reducing stocks for South American fishing communities.
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.
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.
How do these events affect us?
The extreme weather events caused by El Niño and La Niña affect infrastructure, food and energy systems around the world.
The drought in Canada and Asia caused by the 2014-16 El Niño phase resulted in crop failure and damaged the food security of more than 60m people, according to the UN Food and Agricultural Organisation.
During El Niño events, less cold water rises to the surface off the Americas which brings fewer nutrients from the bottom of the ocean.
That means there is less food available for marine species like squid and salmon, in turn reducing fish stocks for South American fishing communities.
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.
However, it also said that historical evidence like tree rings, corals and sediment records shows that 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 El Niño or La Niña 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.
But scientists are not certain this will happen.
Graphics by Visual Journalism team.
Related TopicsRelated Topics
El NiñoEl Niño
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