Snowfall in western New York being measured in feet, not inches
One of the strongest storms ever recorded
A relentless snowstorm
Record rainfall
Record-breaking rainfall
With a new UK record temperature
Earth is increasingly experiencing extreme weather...
...wreaking havoc across the world...
...devastating ecosystems, economies and communities
When catastrophic weather strikes, it’s often blamed on climate change...
...but there are also natural phenomena at work
El Niño and La Niña...
...are opposite states of one of Earth’s most important climate processes...
...the El Niño Southern Oscillation or ENSO
These extremes impact people everywhere around the world
But what is ENSO? How does it work?
And what kinds of extreme weather do El Niño and La Niña cause?
In the 17th century, Peruvian fishermen noticed periods of unusually warm water...
...in the Pacific Ocean
They called this phenomenon El Niño, the boy in Spanish...
...named after Jesus, as it occurred around Christmas
It wasn’t until the 1960s that meteorologists realised...
...that this was linked to the Southern Oscillation...
...which refers to changes in atmospheric pressure...
...between Darwin, Australia, and Tahiti in the central Pacific
The two names were combined...
...and the El Niño Southern Oscillation, or ENSO, was coined
The key thing about ENSO is that there are three different states
There’s a neutral ENSO state and there are two extreme states, El Niño and La Niña
ENSO is an interaction between water in the Pacific Ocean and the atmosphere above...
...measured in changes to sea-surface temperatures and atmospheric pressure
But to understand ENSO, you’ve got to know which way the wind blows
In the neutral phase, winds sweep along the equator...
...from east to west across the Pacific Ocean
These are known as trade winds
They move surface warm water...
...in the same direction, away from South America...
...towards Asia and Australia
The layer of ocean between this surface warm water and cold deep water...
...is called the thermocline
With more surface warm water...
...now in the western Pacific, the thermocline is pushed down but rises in the east
This leads to a process called upwelling
Because you’re pushing some water away to the west...
...other water comes up from below...
...and this water tends to be colder and also richer in nutrients...
...and that’s why you have very rich fisheries...
...off the west coast of South America
During a neutral phase...
...sea-surface temperatures remain close to their long-term average
These conditions can last for years, but they’re broken...
...if they’re pushed into one of two intense states, El Niño or La Niña
When this happens, the world is more likely to experience extreme weather
El Niño is talked about as the warm phase of ENSO
Normally what seems to start off an El Niño...
...is that the trade winds which push the water away from South America weaken
They stop pushing warm water west
Instead, it remains in the eastern and central Pacific
Those trade winds can even start blowing in the opposite direction...
...pushing warm water back east towards the west coast of the Americas
The thermocline in the east is pushed deeper...
...and can sometimes completely flatten out
El Niño basically kind of puts a cap on the upwelling...
...because as the warm water moves back, it’s harder for the cold water to come up
What you find is that the fisheries decrease...
...because the amount of nutrients for the plankton that the fish eat reduces
Definitions vary by country...
...but generally in the middle of the Pacific, along the equator...
...in what’s known as Niño region 3.4...
...sea-surface temperatures have to be at least...
...0.5 degrees Celsius above average to be declared as El Niño
And it has far-reaching effects on ecosystems and livelihoods around the world
Scientists blame El Niño
Forecasters now say a so-called Godzilla El Niño could be developing
They fear that the El Niño will bring yet another season of drought
Areas in the northern United States and Canada become drier and warmer...
...Central America is hit by drought...
...and intense tropical storms also become much more likely...
...on the west coast of the Americas
You get really quite wet weather in parts of Peru
You get dry weather in parts of Brazil
Because you’re moving the warm water...
...towards Latin America and the Pacific...
...then you are drying out some of Asia
So you’re drying out parts of Australia...
...which might then catch fire, you’re drying out Singapore
But it goes beyond that part of the tropics
You can expect to see quite a lot of rain and thus possibly flooding...
...in parts of East Africa, maybe something drier in West Africa
One of the most severe El Niños in history started in 1997
Many scientists believe the upcoming El Niño will be even stronger...
...and some are already calling it in advance...
...the climate event of the century
It brought devastating drought to Indonesia, Malaysia and the Philippines...
...while Peru saw heavy rains and floods
The extreme weather associated with this El Niño...
...was the cause of 23,000 deaths worldwide
The damage is estimated to have cost between $60 to $180 billion in today’s money
It also led to record global temperatures
The oceans store up much more heat...
...from global warming than the atmosphere does
And during El Niño, with more warm water at the surface...
...that effectively means that more heat can get out of the ocean...
...and that’s why typically El Niño years are warmer worldwide
But after about nine to 12 months, this phase of ENSO usually comes to an end
Effectively El Niño gets tired...
...and the feedback mechanisms that are holding it together...
...one or other of them will break down...
...and it will flop back into the neutral phase
Hi, I’m Oliver Morton
I’m a senior editor at The Economist
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Having returned to ENSO-neutral, those trade winds blow from east to west...
...but if they keep getting stronger...
...they can push ENSO into another extreme...
...the cool phase, La Niña, or the girl in Spanish
Powerful trade winds now push even more surface warm water west towards Asia
The thermocline becomes shallower in the eastern Pacific...
...increasing upwelling off the coast of the Americas...
...more cold nutrient-rich water is brought to the surface
A La Niña event is generally declared...
...when sea-surface temperatures in Niño region 3.4...
...become 0.5 degrees Celsius colder than average
La Niña is great if you are...
...fishing for anchovies off Peru because much more upwelling...
...so more food for fish and so more fish
So there are silver linings to the extreme states of ENSO...
...but La Niña is still responsible for plenty of destruction around the world
Hurricanes in the Americas become more likely on the east coast
By early 2023, Earth had been in La Niña for three consecutive...
...northern hemisphere winters...
...which is highly unusual for a pattern that normally lasts nine to 12 months
La Niña was associated with devastating extreme-weather events across the globe
Heavy rain led to serious flooding in many countries...
...from Australia to South Africa
Drought was widespread, with Argentina...
...and China among the places that were hit particularly hard
We’ve had a sort of like chain of La Niñas now...
...and I think far away, the biggest human impact has probably been...
...the drought in East Africa...
...which has threatened the food security of tens of millions of people
You could also point to the floods in Pakistan last year...
...which fit into a La Niña pattern and were particularly severe
33m people were affected and almost 2,000 lost their lives
Flood damage and economic losses amounted to over $30bn...
...9% of the country’s GDP
The fact that La Niña made the world as a whole a little bit cooler...
...doesn’t mean it wasn’t very hot in Pakistan...
...and that meant that the rain clouds could hold more water...
...and that meant that the floods were particularly intense
ENSO isn’t the only factor causing extreme weather like this
Global warming means glaciers in the...
...north of Pakistan are melting faster, which also contributed to the floods
So the double whammy of climate change and the effects of ENSO can be disastrous
One of the things that’s been striking about this recent La Niña is despite...
...that cooling effect, the world has been hitting...
...near-record temperatures every year for the last few years
So with La Niña keeping a lid on global temperatures...
...imagine how hot Earth could get when it moves into the warm phase
But exactly how ENSO is being affected by climate change remains unclear
Since 1950, El Niño and La Niña phases have been getting stronger...
...leading to more significant changes in sea-surface temperatures
If you look at long-term records of the climate, not human records...
...but records from the environment...
...you find that ENSO has been varying for thousands, tens of thousands of years
So it’s very, very hard to say that the changes that appear to have happened in ENSO...
...in the last 50 years are definitively due to climate change
When you ask different climate models...
...about what ENSO looks like in a warmer world...
...some will say one thing and some say the other
The Intergovernmental Panel on Climate Change has said there’s no consensus...
...on whether there will be a change in ENSO-related sea-surface temperatures...
...in the next century
But the one thing most climate models do agree on is that due to global heating...
...ENSO’s effect on rainfall variability...
...will increase over the east-central Tropical Pacific
So with El Niño, this region will see even more rain...
...whereas during La Niña it will be drier than usual
Over a third of the Earth’s population lives in the tropics...
...and they face a climate which changes from year to year with El Niños...
...and La Niñas in ways that other people just don’t normally experience
ENSO is a terrible thing for the tropics...
...but it is at least somewhat predictable
Perhaps the most important thing that the world as a whole can do about ENSO...
...is take it seriously and move resources...
...to the places where they are needed in advance of the weather patterns
One forecast is certain, ENSO will continue to be one of the most powerful forces...
...to influence Earth’s climate
If you want to know more about El Niño...
...and La Niña, we’ve produced an interactive article...
...on ENSO that shows you more details on how it works
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