Original subtitles

What connects seemingly random events

like floods in the United Kingdom,

droughts in Africa,

wildfires in Canada

and cyclones in the Pacific?

A boy.

"El Niño" in Spanish.

It's the innocent-sounding name

that Peruvian fishermen gave

to a climate phenomenon that regularly devastates our world.

There is no single phenomenon in the world

that can affect global weather patterns

as much as El Niño

and is, therefore, associated

with as many natural disasters as El Niño is.

One major El Niño event

that started in 2015 and which only ended in 2016,

contributed to catastrophic weather events

right across the globe.

El Niño of 2015-16 was one of the major

and most intense El Niños

that we've seen in the historical record.

It contributed to the longest coral bleaching ever recorded,

stretching across the oceans

from Florida Keys to the Great Barrier Reef.

Africa, Malawi, Zimbabwe, South Africa,

Mozambique and Ethiopia all suffered devastating drought,

inflicting hunger and disease on millions.

South America struggled to cope

with both drought and extreme storms.

The Pacific Ocean's vulnerable, low-lying islands

were hit by several cyclones, one after the other.

And southeast Asia recorded

the largest emissions of wildfire and smoke ever.

So extensive was El Niño's impact

that it even played a part in major disasters

across Europe.

The United Kingdom was hit by wave after wave

of record-breaking storms and floods.

Floods can kill. Floods annihilate.

They destroy. They're incredibly dangerous.

In this episode of Deadly Disasters,

we will look at this climate phenomenon

that has affected the entire world for millennia.

Our experts will look at some

of the most catastrophic consequences of El Niño,

and its little sister, La Niña.

another climate event

with devastating effects around the globe.

Many of them are immediately felt,

and they cause death and destruction and disruption.

We will examine the differences and similarities

between these two climate-changing incidents.

We will consider how different countries

have managed their impacts,

particularly in the developing world,

where resources can be stretched thin.

Eyewitness reports will tell the human story behind El Niño

and the personal toll these disasters take.

El Niño is a climate phenomenon that happens every few years,

when the waters in the eastern tropical Pacific Ocean

get unusually warm.

Normally, this warm water,

and the rainy conditions it causes,

are in the western Pacific.

There, the sea level is naturally higher.

In fact, normally around 40 to 50 centimeters higher

near Indonesia than Ecuador.

This is, in part, because of strong trade winds

blowing westward across the Pacific.

They push water toward Asia and Oceania,

where it gathers and creates a slightly tilted ocean surface.

El Niño causes droughts in normally damp areas

in the eastern Pacific,

such as Indonesia and Australia,

while normally drier places,

like South America's west coast,

endure devastating floods.

But it also impacts the global atmospheric circulation.

It can weaken the Indian monsoon,

while bringing heavy rain to the western United States.

We are only just beginning

to understand this powerful phenomenon.

Essentially, El Niño is quite a new science.

El Niño have only really been known about for about 100 years,

and it's only been observed properly for about 40 years,

during which time there's been maybe four big events.

The first recorded scientific discussions

of El Niño were in the 1890s,

between the Lima Geographical Society

and the International Geographic Congress.

But we now know that it stretches at least as far back

as 10,000 years,

to the beginning of the Holocene Epoch,

and the end of the last Ice Age.

We have detected chemical signatures

of increased rainfall and warmer seas

in coral samples and other paleoclimate indicators

since the previous Ice Age.

Climate scientists have also shown

that tree-ring records from North America,

especially from the Southwest,

match the intensity of El Niño events

over the last 1100 years.

These tree rings coincide well

with the 150 year sea surface temperature records

we have from the Pacific.

During El Niño,

the warmer surface temperatures in the eastern Pacific

change the atmospheric circulation.

This causes unusually wet winters

in the southwest United States, and thus wider tree rings.

This research was used to help improve El Niño prediction

in climate models.

Predicting its likely events

over a few months ahead is now normal.

But our recognition of El Niño

and its impacts is helping us look at our history

with fresh eyes.

For instance,

we know that from 1789 to 1792,

the South Asia monsoon failed many times.

Research suggests the El Niño

influenced a mix of climate anomalies,

and unusual weather led to crop failures in Europe.

This, in turn, became the catalyst

for some of the troubles and desperate anger that,

in 1789, erupted into the French Revolution.

El Niño has been linked to at least three large famines

in the late 19th century.

British and Indian officials

noted that extreme weather

and the collapse of monsoon circulation

resulted in great droughts and floods.

Between 30 to 60 million people died in China,

India and Brazil.

Hundreds of millions endured hunger.

It was only in the 1960s

that scientists definitively linked

the alternating warm and cool patterns

in the Pacific waters

and the atmospheric circulation.

At least 26 El Niños were recorded in the last century.

In 1957-58,

El Niño caused serious damage

to the Californian kelp forests.

It was only in 1982-83

that scientists were able to study a major El Niño

as it was actually taking place.

The unusually warm waters in the Pacific

forced fish to seek out colder waters to survive.

On Christmas Island,

sea birds abandoned their young

to fly over the Pacific desperately searching for food.

Almost a quarter of the fur seal and sea lion populations

off the Peruvian coast starved to death.

Some of the biggest effects on wildlife

that we've known about for the longest with El Niño

is what happens off Peru.

You have deaths of sea birds.

You have deaths of seals, and in some years,

collapses in population of Galapagos penguins.

Indonesia and Australia faced terrible droughts

and Southeast Asia shut down some of its airports

because of the thick plumes of smoke rising from forest fires.

El Niño is associated with extreme weather

and natural disasters in many, many countries in the world.

In Spanish,

"El Niño" translates as "The Child" or "The Boy."

The name was given by Peruvian fishermen

who noticed the occasional warming of the ocean

around December

and made the connection to Christmas and Jesus.

El Niño and La Niña,

which translates to "The Girl,"

are opposite phases

of the El Niño Southern Oscillation cycle of ENSO.

ENSO is the name for the temperature variations

between the ocean and atmosphere

in the Equatorial Pacific.

El Niño is the warm and La Niña the cold phase of the ENSO.

El Niño is officially declared

if the eastern tropical Pacific's surface temperature

rises half a degree centigrade above the long-term average.

One of the most severe El Niño events was in 1997-98,

when the Pacific heated up remarkably,

by more than three degrees centigrade.

The effects of climate change

on the cycle are not yet fully established.

Some scientists believe climate change

will make ENSO events more frequent and intense.

If right, it is likely that the economic,

environmental and societal impacts

will only get more extreme.

The three most deadly El Niños,

1982-83,

1997-98 and 2015-16

were not just because

of the scale of the chaos they wreaked.

But also because of how unpredictable

their effects were.

It is not certain what tips

the unstable Pacific Ocean atmosphere system

into El Niño,

but a weakening of normal trade winds that blow west is key.

For instance, in 2014,

a large group of very strong thunderstorms over Indonesia

may have been the trigger.

An upwelling or upward movement of ocean water

can mix upper and lower levels of seawater together.

This brings cool and nutrient-rich water

from the bottom of the ocean to the warmer surface.

There, it supports large populations of phytoplankton,

zooplankton, fish, and fish-eating seabirds.

Every few years,

normal upwelling in the Pacific Ocean is affected by ENSO.

During an ENSO,

the trade winds that blow from east to west weaken.

This allows the warmer waters of the western Pacific

to move towards the western coast of South America.

This suppresses the normal upwellings of cold,

nutrient-rich water.

The marine food chain is disrupted.

Warm waters force fish down to colder, deeper water.

Seals suffer as they lose their food source.

In the same way, the fishing economies

of countries such as Peru and Ecuador are also hit.

We are still trying to work out

the relationship between El Niño and climate change.

What will happen to El Niños

under climate change, global warming,

is a question that many people ask.

Some studies are suggesting

there may be an increase in frequency and intensity,

but other studies suggest that that may not be the case.

So at the moment, there isn't a strong consensus

about future behavior.

But the global system is changing

because of global warming,

so we're very likely to see a change

in the patterns of El Niño.

We know that a rise in global temperatures

leads to an increase in sea surface temperatures.

This is what sparks the El Niño phenomenon.

The relationship between El Niño and a change in climate

is somewhat cyclical.

Oceans act as carbon sinks:

they capture and store carbon

as dissolved CO2.

And carbon dioxide dissolves more easily in colder waters.

During El Niño,

sea surface temperatures increase.

This causes less CO2 to be dissolved.

The result is more carbon dioxide in the atmosphere,

which causes global warming,

which in turn leads to the climate changing.

Bushfires sparked by the El Niño effect

also release large amounts of CO2,

which in turn can lead to greater global warming.

ENSO is one of the most important phenomena

affecting our global climate.

It impacts the atmospheric circulation,

which leads to changes in temperature and rainfall.

The equatorial Pacific climate behaves as a "coupled system."

This is because the states of the ocean

and the atmosphere depend on each other.

Some research suggests El Niño events

are increasing in both intensity and frequency,

resulting in increased extreme weather events.

For instance, unusually hot weather

is becoming more frequent in Sri Lanka.

Certain regions have suffered record temperatures,

as well as very heavy rains.

These extreme events cause severe damage to crops,

depriving farmers of a stable income.

Fishermen also suffer when heavy rains

stop them from going to sea.

Natural disasters such as floods

and landslides become more frequent,

leading to loss of lives and homes.

Diseases spread, roads are blocked,

food prices soar,

and countries' vital infrastructures are destroyed.

In 2015, El Niño struck with particular ferocity.

Its effects were widely felt

and devastated vast areas across the globe.

There was a very extensive disruption

to the rainfall patterns.

And that was associated with food security problems

throughout the globe,

particularly in parts of Indonesia

and also parts of Africa,

with up to about 60 million people

faced with food security issues

directly associated with that event.

Countries across southern Africa

experienced a bewildering array of extreme weather.

South Africa experienced one of its worst droughts

for 30 years.

Many small farmers went out of business.

The government declared five out of its nine provinces

drought disaster areas for agriculture.

Dams were at an all-time low.

Thousands of hectares of land were left with brittle stalks

from the previous year's harvest.

The effects on wildlife were dramatic.

Impala and hippopotamuses grew emaciated.

Buffalo and hippopotamuses died in droves.

But jackals and crocodiles

thrived on the increased food sources.

The United Nations warned

that about 50 million people faced hunger

across southern and eastern Africa,

as the continent struggled with its worst drought in decades.

One of the things about El Niño

is that it does affect very large geographical areas,

and so if we take the example of southern Africa,

you have a drought occurring across multiple countries.

And that can lead to additional problems

to what you might find just internally

if the drought occurs within the country.

The worst hit was Ethiopia.

There, more than 2 million children

needed treatment for malnutrition

and over 10 million people needed food aid.

If the situation continues like this...

we need the international community's support.

The crisis even hit Ethiopians

not at immediate risk of going hungry.

3.9 million children and teenagers

no longer had access to education.

These problems don't go away overnight.

They don't go away in a decade.

I mean, this is a long-haul process.

Somalia, Sudan, and Kenya's crops also failed,

leaving a total of more than 20 million people

food insecure in the region.

The drought took many officials by surprise.

Although El Niño had been forecast,

it normally brings more rain to the region, not less.

When El Niño strikes,

it often exposes weaknesses in countries' infrastructures.

The 2015-16 event

brutally revealed Zambia's overreliance on hydropower.

Ninety-five percent of the country's energy

was generated this way.

When the droughts hit,

the dammed lakes couldn't cope.

Water levels in the Kariba dam,

one of Zambia and Zimbabwe's main sources of hydropower,

fell to a record low of 12 percent in January 2016.

We're seeing a drastic reduction, that's very scary.

And that tells me we're doing something wrong as a country.

We're doing something wrong as a region.

And perhaps, we're doing something wrong globally.

And therefore, this is a call to action

for us to do everything that we must

to reduce the global carbon emissions

to the minimum levels.

Industry was also badly hit.

In Zambia, because of the impacts

of the El Niño on the hydropower,

they had an overall impact on national GDP

of between 1 and 2 percent.

Zambia's copper mining industry

accounts for almost three quarters

of the country's foreign exchange earnings.

It was crippled by the power cuts.

In September 2015,

the mining giant Glencore made a staggering announcement.

As owners of a large part of Zambia's Mopani Copper Mines,

they planned to lay off 3800 workers.

The Anglo-Swiss company

laid the blame largely on the power shortages.

Zimbabwe, famously once the region's breadbasket,

was one of the countries worst hit.

The country's president, Robert Mugabe,

declared a state of disaster.

In less than a month,

people needing food aid rose from 3 to 4 million.

Even cocoa bean yields were badly affected,

meaning its price hit a four-year high

as a result of the drought.

And production was lost

in the world's major cocoa producer, the Ivory Coast.

Farmers whose families had relied on the cocoa bean

for generations were forced to hunt for other work,

often illegal and dangerous, or starve.

Such was the scale of the destruction

that in the summer of 2016,

the southern African countries launched an emergency appeal.

They asked for $2.8 billion,

to help them feed the almost 40 million people

suffering in the worst regional droughts for 35 years.

But the very scale of the droughts

made giving help particularly difficult.

International organizations

despaired of providing resources to match the need.

Children were forced from home,

leaving healthcare,

security and loved ones behind.

Put simply,

the scale of the crisis far outstripped

the capacity of communities

and the resources of the governments.

In under a year, El Niño

was putting decades of global development gains at risk.

This double contradiction can be seen vividly in Ethiopia.

It suffered from severe drought

in the northern parts of the country.

The droughts inflicted two consecutive

poor crop and pasture seasons.

18 million people needed food assistance in 2016.

This was the greatest need the country had faced

since the 1984 famine,

which sparked the Live Aid campaign run by Bob Geldof.

In contrast, the south of the country

suffered torrential rains and flash floods.

The floods arrived after nearly 18 months of drought

that left communities ill prepared to cope.

The long drought reduced the ground's ability

to absorb water, which exacerbated the floods.

When you have two different types

of disasters in one country,

that provides a particular problem for aid,

because when you have a heavy drought and a heavy flood,

the crops will fail everywhere, but for different reasons.

The myriad of impacts, the unpredictability,

but also the scale of El Niño,

presents international organizations

with almost unprecedented challenges.

This can be seen vividly in the range of devastation

the 2015-16 El Niño wreaked on the Pacific Islands.

It threatened their very existence.

Almost two million tourists

visited the multitude of islands in 2015,

but the Pacific Islands weren't to be spared.

Their small populations,

remoteness, few resources,

and dependency on foreign aid only made them more vulnerable.

The problems associated with extreme events

are made much worse on small island states

because they tend to be remote,

they tend to be relatively poor,

and they don't have easy lines of communication for food,

aid money, shelter, et cetera,

to come into those countries.

For example, a small island

developing state in the Pacific,

it may be half a day's journey from the nearest rich country,

which is probably Australia or maybe Hawaii,

which are themselves relatively sparsely populated,

and aid workers will have to travel to themselves.

And of course,

if harbor, or more importantly, an airfield is damaged

then the planes can't land, and the aid can't come in.

Wave after wave of cyclones swept across the islands:

Pam, Maysak, Raquel.

Pam was the strongest storm

to ever strike the South Pacific.

On Vanuatu, entire villages were destroyed.

Eleven people were killed

and thousands were left without shelter.

There was to be no respite.

Scarcely had the cyclones left

then the islands were hit by drought.

States of emergency were declared in Palau,

the Marshall Islands,

and the Federated States of Micronesia.

Koror, Palau's capital,

recorded its lowest rainfall in 65 years.

People had to ration water to survive.

Wells became brackish or ran dry.

Staple foods such as breadfruit and bananas

shriveled on trees.

Micronesia's islands and atolls

are not always the paradises they can seem from photographs.

They can quickly run out of drinking water.

Relief agencies struggled to bring water to remote atolls,

a day's boat ride from the main islands.

But El Niño damaged the Pacific Islanders' livelihoods

in other ways.

The warmer water has less oxygen.

Less mixing of water

leads to reduced production of microscopic plants and animals

needed for tuna.

Particularly skipjack and yellowfin.

The warmer water in the western Pacific

shifted the tuna's spawning grounds

to the central and eastern

equatorial regions of the Pacific.

This dramatically reduced the catches

for the island fishermen,

having a severe economic impact.

Despite the country's obsession with talking about the weather,

dramatic meteorological events

have been relatively rare in the UK.

However, in 2015, all this changed.

The UK is used to floods. We have regular floods.

Almost every year there is a major flood,

but in 2015, the flooding was extreme.

I don't think anybody was prepared for the extreme flood

that Storm Desmond especially brought with it.

Humid air,

borne by strong southwesterly winds,

dumped huge quantities of rain over Northern Ireland,

Wales, northwest England, and Scotland.

It began with Storm Desmond,

which dropped over 33 centimeters of rain on Cumbria

between the 4th and the 5th of December.

It broke the national record for rainfall in a day.

Sitting in the house, I saw the water

coming up under the tiles. You know.

It's quite frightening.

Horrendous, it's-it's mad.

It's terrible, I don't know what to do.

Carlisle and other areas of Cumbria were flooded.

More than 5000 homes were affected in Cumbria

and Lancashire alone.

We need to make sure they get all the support they need,

get the insurance claim paid quickly,

get them the alternative accommodation,

make sure the council picks up the furniture

and the things they've had to throw out of their houses.

And then try and get them back in as soon as possible.

The average person is out of their home for nine months

after a flood. And after Storm Desmond,

many people in Carlisle

were not back in their homes for two years.

People suffer with post- traumatic stress disorder.

They're anxious every time it rains.

It's a very deeply personal experience.

Storm Eva followed Desmond.

Eva brought with her more heavy rain,

which fell on the already saturated earth.

People don't realize

that just a few inches of water can float a car,

that a few inches of water can knock you off your feet,

that you can fall down manhole covers

that have been lifted by the sheer volume of water,

that little streams become torrents

and people haven't woken up

to smell the floodwater, as it were.

And they don't grasp just how dangerous

flooding can be and how it can kill people.

It can and it does.

The ensuing floods

engulfed thousands of homes and businesses,

swelling rivers and breaking bridges.

River levels stayed high

and over 70 flood warnings were issued

as the rain continued to fall remorselessly.

On the 22nd of December,

communities in Cumbria were flooded again.

For some, it was the third time in under a month.

It's not Christmas to us in Carlisle,

I don't think at the moment.

You don't feel very festive when you've been through this.

We did all the topographical surveys.

We worked all the measurements out,

built a flood bund last year and the year before,

installed pumps this year,

nearly finished paying for it,

but unfortunately, I'm told there is a foot of water

in church this morning.

On Christmas Day,

more than 100 flood alerts and warnings were issued,

as Storm Eva battered the country.

There was to be no respite.

Once again, northern England was the worst hit.

On Boxing Day,

people in West Yorkshire and Lancashire

had to be evacuated as flooding hit Leeds,

York and greater Manchester.

There are no words that describe the devastation.

Roads were washed away.

Bridges were washed away.

Flood defenses were overtopped and breached.

People's homes were flooded to the ceiling

and businesses were annihilated.

Among the rivers to burst its banks

was the River Ouse in York,

where 500 homes were flooded

and the Army was called in to help.

I'm now left feeling really, really angry.

I've got two little boys who are out of their houses.

We don't know where we're going to be living.

It's going to take months and months

and months for this to be restored.

The inconvenience is indescribable.

Individuals suffered hugely.

Having been flooded myself,

I know how awful being flooded is.

And I don't think anybody can convey

the true awfulness of being flooded.

But people's houses,

because of the sheer volume of water,

will have found that their furniture

wasn't where it was when they left it.

It will have been covered with a thick,

horrible smelling, sludgy brown filth

and going into their homes--

The smell-- You cannot describe the smell.

It really gets you at the back of your throat,

and no filming will ever tell you

how truly awful the smell will be.

Many communities were still trying to recover

from the aftermath of Storm Desmond.

Hundreds of people were forced to evacuate their homes,

as rivers burst their banks in the Cumbrian towns

of Appleby, Keswick and Kendal.

Scotland, northern England

and Ireland were all overwhelmed.

Flood defenses failed to cope with the rain

cascading through the rivers.

If these defenses had not been in place,

you're potentially looking at as much as two meters more water.

That's six feet more water going into people's houses.

So the tens of millions that have been spent on defenses

has been really valuable.

Tens of thousands of properties were also left without power,

dozens of schools were closed,

around 40 bridges were either damaged or shut,

and rail links were severely disrupted.

It's not a quick fix.

It takes a long time to recover.

And in fact, some people haven't recovered from it to this day.

It truly is life-changing.

The Army had to be drafted in to help with the evacuations.

That means supporting the work of the police,

the environment agency,

and all the other people that are now deployed out here.

And we're working alongside them

and will continue to do so for as long as it takes.

Even the Royal National Lifeboat Institution

was called upon to help.

So when you've got extreme floods like that,

and you've got hard engineered defenses

overtopped and-and breached,

and you see trees coming down the hillsides

and loads and loads of rocks,

it's very difficult to actually stop that from happening.

In Tadcaster in north Yorkshire,

the town's bridge collapsed.

It split the town in two.

Residents had to take a 16-kilometer detour

to get from one side to the other.

The floods made giving help particularly hard

as they swept through the town's only medical center.

In their descriptions of the event,

residents compared the town to a warzone.

The Royal Air Force used helicopters

to drop huge sandbags

into the breach of the River Douglas.

The UK's meteorological office

analyzed the reasons for the December floods.

They confirmed that El Niño

had contributed to a persistent weather pattern,

which led to unusually warm, moist air reaching the UK.

I don't think people are aware that a disaster as such

may happen because of climate change

and because of effects like El Niño.

It's an unusual concept to get our heads around.

I don't think people have the first clue

that something that happens in the Pacific Ocean,

where the Pacific Ocean is heating up,

can possibly bring so much rain to our country.

It's something that we've got to become aware

that may happen more in the future.

December 2015

turned out to be not just the wettest December on record,

but also the wettest month ever in the UK.

The UK is still grappling with the problems of storms

and the floods they bring,

even though changes have been made to infrastructures

and how the country responds.

The sheer scale of the challenge

has led the government to change its approach

from one of protection

and building higher flood defenses,

to improving communities' resilience and infrastructure

to when floods do happen.

Organizations like local wildlife trusts

are advising on better landscape management

such as installing flood storage areas,

planting trees, and getting farmers to plow across slopes

to slow the flow of water.

In one of the worst hit villages,

Glenridding in Cumbria,

thousands of tons of gravel were removed from the river,

walls were raised, and drains improved

to reduce the risk.

The floods themselves actually cost about £1.6 billion,

and that's government statistics.

But obviously the-- A lot of people weren't insured,

so they weren't able to apply for flood insurance.

The 2015-16 El Niño

was as remarkable for its reach

as for its range of extreme weather impacts.

Countries across five continents

called states of emergency.

It brings extremes from both ends of the spectrum,

sometimes both in the same place.

A clear example of this

is the 2015-16 winter in Canada and the United States.

December 2015

set records as the mildest in 120 years.

Some places in the Midwest and East

were as much as nine degrees Celsius warmer than normal.

Then, as the new year arrived,

so did the cold.

The east coast and southern United States

were plunged into well below average temperatures,

and many saw snow.

But this was only the beginning of what was to come.

The coastline was soon to be hit by a giant blizzard.

Between the 20th and the 22nd of January 2016,

governors of 11 states and the mayor of Washington, D.C.

declared states of emergency

in anticipation of heavy snowfall and strong winds.

On Saturday, the 23rd of January,

Blizzard Jonas hit.

New York City was paralyzed.

The blizzard dropped 69 centimeters of snow

on Central Park.

This was the most snow the park had seen

since records began in 1869.

Governor Andrew Cuomo issued a travel ban

for New York City and Long Island roads

on Saturday afternoon.

Mayor de Blasio said that drivers

who violated the ban could be arrested.

Snow fell even in southern states

that are rarely associated with white winters.

Georgia and South Carolina

reported as much as 19 centimeters of snow cover.

Louisiana and Mississippi

both reported over 5 centimeters in some areas,

and one town in Alabama had as much as 9 centimeters.

West Virginia received the most snow,

getting a whopping 106 centimeters

in the town of Glengary.

Jonas battered the country

with 126 kilometer per hour gusts,

and sustained winds of up to 91 kilometers per hour.

By Monday, the 25th of January,

the storm was still going strong.

Schools all over the east coast were closed,

as were federal offices in Washington, D.C.

People were bunkered up in their homes,

unable to leave.

Hundreds of thousands of people lost electricity

during the storm.

When the winds finally subsided and the snow let up,

over 100 million people had been affected by Jonas.

As many as 13,000 flights had to be canceled.

And, worst of all,

at least 48 people had been killed.

Storm Jonas was what is called a Nor'easter,

a cyclonic storm named after its northeastern winds.

While Nor'easters can occur at any time of year,

they are most common in the winter months.

One notable difference between a rainstorm and a snowstorm,

is that snow has a tendency to stick around.

Water runs off, dries up,

and is absorbed by the ground,

but, unless temperatures rise above freezing,

snow stays right where it lands.

This means a lot of work for cities and communities

to clear the snow off roads,

roofs and vehicles.

It can take days for even a well-prepared city

to recover use of all roads.

For those not used to snowfall, the situation is much worse.

Uncharacteristically,

in the 2015-16 El Niño,

Peru wasn't affected.

The year after, however,

serious rains and floods struck the country.

Between January and February 2017,

a region of northern Peru and Ecuador,

which is a desert region,

received considerable amounts of rain.

Rivers burst their banks.

Houses were under a meter or sometimes...

sometimes two meters of water.

This resulted in considerable destruction to infrastructure

and property and fatalities.

And this is particularly difficult

for the region to deal with

when you consider that it's a region

that often receives just a few millimeters of rainfall

or no rainfall at ll.

And suddenly, it received

several tens of centimeters of rainfall

in a very short period of time.

The wet weather was caused

by a warming of the ocean

off the coast of Peru and Ecuador.

The locals referred to it as an El Niño.

But the rest of the world remained unaffected.

This illustrates just how limited our understanding

of the El Niño Southern Oscillation system is.

Scientists across the world can't always agree

on what is and what isn't an El Niño.

Some of Peru's poorest were most severely hit.

Many had set up home in gulches and canyons

that opened from the mountains onto the coast.

Dry for years,

they suddenly turned into raging torrents,

engulfing and sweeping away whole shanty towns.

The rains also washed rubbish,

chemicals and metals from towns,

mines and farms into the Pacific Ocean.

Warm coastal waters drove out schools of Peruvian anchovies,

depriving birds of their main food supply

and forcing them to hunt elsewhere.

Two thirds of the Guanay cormorants

on the south-central coast abandoned their nests.

On top of the effect on the ecosystem,

losing the birds reduced the guano,

which is still mined in the area.

Tourists in Machu Picchu were stranded by mudslides

and had to be airlifted to safety.

Peru's 2017 El Niño event

was one of the most costly disasters to hit Peru

since 1997-98.

It underlined again how unpredictable

and ill-prepared we were to deal with its chaotic effects.

The recovery from that can take a very long time,

particularly in relation to investments,

in rebuilding infrastructure,

so roads and bridges and so on,

to get the money to be able to recover

and rebuild that infrastructure

can take a poor country an extremely long time.

If El Niño's erratic nature

was not difficult enough to deal with,

the phenomenon has a twin sister,

La Niña.

La Niña is the opposite,

the cold phase of the El Niño Southern Oscillation.

It happens when sea surface temperatures

in the central Pacific Ocean fall below normal.

In the United States,

a La Niña winter means more rain in the Pacific Northwest,

short spells of below-average temperatures in the Northeast,

and generally dry and mild conditions

for the southern states.

Whilst an El Niño can spark

streams of moisture into California,

a La Niña winter stops storms

from delivering snow and rain to the region,

leading to droughts.

Western Canada and the Northwest

suffer the most from storms during a La Niña winter.

La Niña makes winters in the Northeast

extremely unpredictable.

They can range from colder and drier to milder and stormier.

La Niña also creates perfect conditions for cyclone systems

over the Atlantic.

Lasting from 10 to 12 months,

La Niña does not always develop

immediately after an El Niño.

However, evidence suggests that strong El Niños

are more likely to turn into La Niñas.

Quite regularly, you will find that an area

that was affected by an El Niño

is then immediately affected by the La Niña that comes after it.

Having an El Niño and La Niña year in quick succession

can be devastating for a country,

particularly countries that are poorly resourced,

poorer countries.

Alarmingly, La Niña years

have clearly shown greater average annual losses

in comparison to El Niño and neutral phases.

Much of the increase in losses during a La Niña year

is due to tropical cyclones making landfall

more frequently in the Atlantic Ocean basin

and increased flooding across the Asia Pacific.

It is believed there have now been three "super El Niños"

in just over three decades,

suggesting these "super El Niños"

might start occurring once every 10 years,

instead of once every 20.

El Niño, and its twin sister, La Niña,

are a strong reminder

to communities vulnerable to changing weather patterns.

They are going to need longer-term help adapting.

The UN has warned that humanitarian disasters

are to be expected with climate change.

We can see how the effects of El Niño

can combine with climate change

most starkly in the Pacific Islands.

Although the relationship between El Niño and drought

in the region is well known,

it remains unclear how global warming might alter

the El Niño phenomenon in the future.

The islands' residents are deeply anxious.

Rising sea levels are already swallowing

the little land they have.

They also threaten water supplies,

as the waves that can make groundwater saline

become more frequent.

It is rainfall's variability,

not average rains,

that mainly drive drought here.

And the main source of variability is El Niño.

The study of the El Niño Southern Oscillation

is a relatively new field of research.

We are still struggling to understand its unpredictability

and how we can mitigate its effects.

Our forecasting is based on data

gathered over a quarter of a century ago.

More recent research and satellite data

suggests that the impact of El Niño Southern Oscillation

is much wider than originally believed.

Europe, Africa, Asia and North America

are all likely to have been affected

in ways we hadn't realized:

air temperatures, rains,

and in North and South America,

significant impacts across a larger area than we thought.

Factors like climate change are only likely to increase

El Niño Southern Oscillation's unpredictability.

El Niño and La Niña

are challenging governments and international organizations

to consider and build this unpredictability

into their planning.

We still grapple to understand the full impact

of El Niño's Southern Oscillation.

The only certainty seems to be the misery and devastation

brought in its wake.