A Place to Live Supersized Earth

This is our home.

From up here, it looks the same as it has done for thousands of years.

But get a bit closer and you can see we've made a few changes.

'We're redesigning our world.'

Three, two, one...

Whoa!

'Wherever you look...'

Just don't, whatever you do, look down.

'..you'll see the scale of this supersized transformation.'

Our generation is changing the face of the planet as never before.

I'm Dallas Campbell,

and in this series I'll show you how we're shaping the modern world.

We're building faster than ever,

transforming whole landscapes in the blink of an eye.

I've got DIY projects in my house that have taken longer than

it's taken Shanghai to build an entire city.

We're opening up the earth...

..and conquering the sky, making it a place we can call home.

BUSTLING VOICES

-Do you get nervous at all?

-Yes.

-Get a little bit scared?

-Yeah.

I'll join the people who'll make the impossible, possible.

This is clearly one of the most dangerous jobs in the world.

I can't believe someone's actually thrown away a horse!

That's the kind of stuff you find in the sewage.

-Thank you very much.

-You're my hero!

Our world is becoming a man-made world.

HE EXHALES DEEPLY

This is it.

This is as high as it's possible to climb

on any man-made structure on the planet.

I'm over 800 metres high. That's more than half a mile above Dubai.

And this is the world's tallest building.

A building like this would have been inconceivable a generation ago.

But it's testament to what we can do now.

Today, we build man-made mountain ranges

stretching as far as the eye can see.

But the story of how we scaled these heights started a long time ago...

-CAT MEOWS

-..and right on our doorstep.

-MAN RINGS BICYCLE BELL

-Morning, vicar!

For thousands of years we've had a passion to build high.

In fact, Britain itself was once home to the tallest building in the world.

In the Middle Ages,

Lincoln Cathedral became the tallest building the world had ever seen,

breaking the record that Egypt's Great Pyramid had held

for almost 4,000 years.

But if you think about it, the pyramid is almost solid stone.

It was designed as a mausoleum for one person.

This place, on the other hand,

was designed for thousands of people to congregate.

To build so high, the architects of Lincoln had to make

a major construction breakthrough.

If you want to build a building that's high

and has a huge internal space, a space that people can use,

a space that people can actually come together,

then you really need to rethink your engineering techniques.

The medieval builders had to come to terms with the forces of gravity.

HE PANTS

And to see how they did it, so do I.

Oh, it's beautiful. Wow.

The architects stripped as much stone from the structure

as they dared, leaving just enough to keep it standing.

If you just think about the physical forces

that are at play on this building,

all these huge bits of structure leaning against each other,

creating this perfect balance.

And you can see from here how it all fits together.

A network of hundreds of arches, ribbed vaults and columns keep this building standing.

They're like the cathedral's stone skeleton.

The ribbed vaults help spread the immense weight of all the stone.

The pointed arches channel the load down through the columns.

To give the cathedral its height,

an enormous stone tower is supported on just four great pillars.

Nearly 700 years later, this vast building remains rock solid.

But to be the world's tallest building,

the medieval cathedral was once even higher.

The current height of the cathedral is 80 metres, and it is magnificent.

But what's even more spectacular is what you can't see,

because actually, back in the day, it used to be a lot taller.

Building high back then was about making a connection with

the heavens, getting closer to God, so they just kept on going.

Three enormous spires were built on top of the cathedral's towers.

The largest, standing at 80 metres high,

doubled the height of the building.

The spires stood over two centuries before collapsing in a storm.

But with them, Lincoln Cathedral was 14 metres taller than the Great Pyramid.

To build higher than that

required a revolutionary new building material - steel.

Inspired by the engineering of the Industrial Revolution,

the Eiffel Tower is almost twice the height of Lincoln Cathedral.

In 1930, New York's Chrysler Building was the first "world's tallest" to use a steel skeleton.

And just one year later, the mighty Empire State Building

used the new construction method to go even higher.

The next major breakthrough came in 1972

with New York's sleek and very tall World Trade Centre.

And soon after, Chicago's even taller Sears Tower.

Glass walls fixed to a completely steel structure made this building much lighter.

Later, the Petronas Towers in Kuala Lumpur used steel and glass over an outside frame of concrete

which was built around a reinforced central concrete core.

This provided the strength and the shape.

Skyscrapers no longer needed to be box-like.

They had become works of art.

Taipei 101 was the first building to reach half a kilometre high.

It was hard to imagine going any higher.

These are the deserts of Dubai.

It's in this dry and windy landscape that the world's first mega-tower has risen.

And it's rewritten the record books.

I'm standing in a shadow that's being cast by a structure

with a unique claim to fame.

It's about a mile-and-a-half or so in that direction

and over half a mile in that direction.

And at 829 metres, it dwarfs every other building on the planet.

Look at it.

It is ridiculous! That is off the chart.

The engineers had no blueprint to copy

when building the world's first mega-tower.

What they came up with wasn't always as hi-tech as you might imagine.

It looks so fragile and elegant, but if you take away all the glass,

you can see it's actually held up by good, old-fashioned brute force.

330,000 cubic metres of concrete.

The Burj Khalifa has a frame made entirely of reinforced concrete.

During its construction, liquid concrete was packed in ice

to stop it setting in the desert heat,

and then pumped 600 metres up.

That took a pressure of a massive 200 atmospheres.

Its final height advanced the "world's tallest" record

by a staggering 320 metres.

That's equivalent to an extra Eiffel Tower.

Brute force raised the tower,

but keeping it standing isn't about strength alone.

It's also about clever aerodynamics.

-Welcome to the Burj Khalifa.

-Pleasure, thank you for having me.

-Please follow me.

-Thank you.

To understand this for myself,

I'm heading to a place few people are ever allowed to go.

-Dallas, floor 160.

-Thank you very much.

I'm really nervous.

-Dallas, do you want to come over?

-Yeah, I'm coming.

-OK, Dallas.

-Yep.

Just step in and I'll check you out.

I was secretly hoping that it was going to be too windy today

and it would all be cancelled and we could all just go home.

Somehow the windows would just clean themselves.

Unfortunately for you, no.

-I'm absolutely terrified. I've never been this scared in my life.

-Really?

Well, you know, it's pretty high up here.

DALLAS EXHALES DEEPLY

-Good. It'll be fine.

-Yeah, that's good.

The leg ones - don't want to be too tight?

Not too tight, so you're comfortable. Right, one more, round here. OK.

-And you are ready to rock. Good to go.

-Let's go to work.

-OK.

After you.

-This is Xiao Lau.

-Hello.

-Good to meet you.

-Barry Hannah.

-Nice to meet you.

-This is Davie.

-Davie, how do you do? Nice to meet you.

-This is Shri Krishna.

-Good to meet you.

I'm going to try and not let you down.

Today, I'm going to join the team whose job it is

to clean the outside of the world's highest windows.

Just pull a little slack through.

Just pull up on this one.

A little bit more. OK, now lock the handle off.

Yeah, yeah. >

OK. OK, just lean back, just lean back.

You're OK, you can't go nowhere.

-I need the bucket.

-Yeah, hang on a second. Take this...

Dry mouth.

Do you get nervous at all?

-Yes.

-Get a little bit scared?

-Yeah.

-I haven't looked down yet.

Now I've looked down!

It's almost inconceivable how high these windows are.

I'm 60 metres above the next platform below,

which is, in itself, 600 metres above the ground -

higher than the previous world's tallest building.

At this height, if I dropped anything,

it could do serious damage.

Building high, there's a load of factors you've got to take into consideration.

One of them is gravity, which I'm feeling right now.

But the thing about gravity is it's very predictable.

It's a force that's going one way.

The thing you've really got to worry about is wind,

because by its very nature it's unpredictable, it swirls around

and it can affect the building - as well as window cleaners.

Surprisingly, very tall buildings aren't in danger of

being blown over, but of being sucked over.

As wind hits them, it can form small whirlwinds, called vortices.

This swirling air can create low-pressure areas that tug at the building.

And if enough of them combine up the tall straight sides,

they could make the tower rock from side to side.

So why doesn't this happen to the Burj Khalifa?

Well, it's taken some careful aerodynamic design.

By stepping the building in as it rises

and introducing angles and curves, the Burj Khalifa breaks up

the desert wind, preventing the vortices from combining dangerously.

The designers call it "confusing the wind",

and they reckon it's the only way to build this high.

It strikes me, being out here, that even though we are in such

a technically advanced building, in order to keep it nice and clean,

you still can't beat a man with a squeegee and a bucket.

It takes three months to clean all 24,000 windows,

and when they've finished, the team has to start all over again.

If you are going to build a building that's truly iconic,

you've got to make it look nice.

-And keep it looking nice!

-And keep it looking nice, exactly, yeah.

Keep going, you're all right. Keep going. Lovely.

Wow, that was intense! I don't know how those guys do it every day.

EXHALES DEEPLY

That was intense. But good.

The tallest structure on the planet shows the extent of our ambition.

The small fishing village of Dubai has been transformed

into a metropolis of over two million people.

In just 30 years,

over 150 skyscrapers have risen from the sands.

And the mighty Burj Khalifa acts like a beacon,

drawing the world's attention to this city in the desert.

It would have been impossible to achieve a generation ago.

Hey, come on!

Get outta here!

The epic scale of our redesign of the Earth

is most obvious in the world's cities.

Almost as many people live in urban areas today

as existed on the entire planet in 1970.

And in 2008, we reached an important tipping point.

For the first time in human history,

more than half of us live in towns and cities.

We've paved over a million-and-a-half square miles of the Earth's surface.

Now, to really understand what that means,

try and imagine all the cities brought together in one place.

A bristling forest of skyscrapers would stretch further than the eye could see.

London, neighbours with New York.

Paris alongside Tokyo.

One vast, sprawling super-city.

But the most amazing thing is if you were to pull together

all of the world's urban areas side by side, then that monster

metropolis would only cover about 1% of the surface of the planet.

In other words, over half of us live together in a space that would

fit comfortably onto an island just half the size of Australia,

or 187 times the size of Wales. That's the country, not the mammal.

When so many of us choose to live in cities,

the challenge is to cram everyone in.

Hong Kong is now one of the most densely populated cities

in the world.

But though it looks like a city of the future,

much of Hong Kong has actually been built

using a scaffolding method from the past.

And this is the wonder material, just good old bamboo.

They've been using this for thousands of years.

As a scaffolding technique, if it ain't broke, why fix it?

Hi, Clement, how are you today?

Good, how are you?

Will you be able to get all this up in a day?

-Yeah.

-Seriously?

-Yeah, yeah, yeah.

It's pretty high, how many floors is that?

It's 13 floors.

So why bamboo, why not steel? What's good about bamboo?

Compared with the metal scaffolding it's much cheaper,

and it's easy to install.

And presumably, as well, I mean, we were watching them,

-you can cut it to size, you just chop a bit off?

-Right, yeah.

If it's very windy,

if there's, like, a typhoon, do you leave the scaffolding up?

-We still leave it.

-It's fine in high winds?

-It's fine.

Does it take a lot of training?

-Over ten years.

-Over ten years!

I'd quite like to have a go and just see how difficult it is.

Bamboo's hollow stem and tough fibres make it light and strong,

and the joints in each pole give it the flexibility it needs

to cope with extreme weather.

The professionals can construct over 100 metres in a day.

I like to think I've contributed my little bit.

-Look at that!

-Yeah. good.

Every year, the demand for living space in Hong Kong increases.

And as more homes are squeezed in, buildings keep getting higher.

Ap Lei Chau is one of the densest residential areas of the city.

Yin Yin Tong's family lives over 70 metres up.

Her children only know a life in the sky.

-In you go.

-OK.

-Right, what floor are we going to?

-The 25th floor.

-25.

-25.

-It's all about elevators, Hong Kong.

Yes, up and down, up and down, down and up.

Yin Yin moved here from England, in 2004.

-So you've left Brighton for your new life in Hong Kong.

-Yes.

And you arrive at your front door in your brand new flat.

-What do you think?

-Blimey, this is small.

It's small, but is this a sort of normal...

I mean, would this be considered small in Hong Kong standards?

No, this would be considered quite big.

-It's a pretty spectacular view, isn't it?

-Yeah, it is.

What about playing, I mean for kids, obviously, they need to run around?

There's a park downstairs.

-Even that's actually raised up, as well.

-Yeah, it is raised.

Everything's slightly raised up.

Yeah, even the netball court is, like, raised up from the ground,

-so nothing is completely on ground level.

-Yeah.

This is worlds away from what Yin Yin grew up with back in the UK.

How is it different, living in a high-rise area?

Well, just everything is geared upwards, basically. You adapt to it.

Most people here live like this, so you have to get used to it.

What kind of mushrooms are these?

These are Korean mushrooms, Korean mushrooms.

You're not supposed to eat them.

You can eat a raw mushroom!

Not Korean ones!

Over 1,000 people live in each of these blocks,

and there are at least 20 of them in this one estate.

So more than 20,000 people live within a half mile radius,

stacked one on top of the other.

Hong Kong has embraced high-rise living so successfully, nearly

three million people make their home above the 14th floor.

That's more than the population of Chicago,

America's third-largest city.

The modern city is extraordinary.

It might just be our greatest invention.

I mean just look around here for example, try and imagine,

try and visualize what all those people living together

actually looks like.

MUSIC: "Warm In The Winter by Glass Candy

# Love is in the air, oh

# Love is in the air, yeah

# We're warm in the winter

# Sunny on the inside

# More warm in the winter

# Sunny on the inside

# Woo! #

It's not just Hong Kong.

Across the planet, hundreds of millions of us

are squeezing into cities that have risen into the sky.

In a single generation, the urban world has exploded in size.

In 1970, just two cities on the planet

had a population of more than ten million.

Now there are 21.

Our future is staked on the success of these vast urban areas.

And to keep a mega-metropolis running smoothly

demands some mega engineering.

This city has a major problem staying healthy.

The reason? It's been built in entirely the wrong place.

So over there, in that direction, just through the smog,

you've got a chain of active volcanoes.

That way, you're right by one of the world's earthquake hotspots.

So, all in all, you'd think it's not really an ideal location

for a city of over 20 million people.

And if that wasn't bad enough, there's something else.

Mexico City is built in the crater of an enormous volcano.

And it's on the move. Downwards.

Just to give you an idea of the extent of the problem, Venice,

which I suppose is the city we most associate with sinking,

is dropping around about seven inches over the last century,

so, you know, the height of a kerb.

Mexico City, by contrast, has dropped around 30 feet,

so about the height of this entire building.

And you can kind of see it everywhere you go in Mexico City.

The whole place is, sort of, undulating.

Nowhere is really level.

In fact, you might be able to see just over there,

where that car's coming, the road is kind of bent and buckled.

The entire city is just slowly sinking downwards.

The subsidence is bad enough at street level.

But Mexico City's problems are even worse under the ground.

The plumbing that keeps the city healthy is failing fast.

120/80.

Esta muy bien.

As the ground sinks,

it reverses the downward gradient of the sewage system,

so instead of all the raw sewage flowing away from the city,

as is customary, it actually starts to flow back towards the city.

And obviously, you know, if nothing's done about that,

it means Mexico City will end up drowning in its own filth.

Engineers have begun work on a new super-sewer.

But until it's ready, professional diver Julio

has Mexico's most unenviable job.

And today, the most nervous apprentice.

Mexico City's sewers get blocked up so regularly,

Julio and his team are forced to dive into the raw sewage

to unblock the pipes by hand.

If you came into contact with raw sewage, how dangerous is that?

What kinds of diseases could you get?

OK, well, that doesn't sound too bad. That sounds all right.

Hey!

'My job today is to help Julio maintain one of the massive pumps

'that keeps the sewage moving.'

When you look at the surface of it, I'd just assumed that was the floor.

I'd assumed people had just dropped rubbish there.

And then I realized that's actually the surface of the water.

It's truly disgusting. And the smell is so bad. It's indescribable!

Several pumping stations, like this one,

force Mexico City's sewage uphill and out of the city.

But the huge underwater pumps regularly become blocked with

rubbish dumped into the sewers.

What exactly are we going to be diving into today?

-Aguas negras?

-Aguas negras.

-Black water.

-Yes.

-Why?

As if I need to ask why it's called black water!

Mexico City, unlike, say, London,

dumps all of its liquid waste into a single sewer,

making this some of the most toxic sewage on the entire planet.

I mean, this is clearly one of the most dangerous jobs in the world.

-How many divers in your team?

-Dos, dos buzos.

-There's two divers for the whole of Mexico?

-Yes.

-That's it?

-Yes.

I shouldn't be surprised that few people want a job this perilous.

One of Julio's colleagues was drowned when he was swept away

by an unexpected surge of wastewater.

-And this is definitely closed?

-Si.

It's closed? Let's just keep it closed, we'll keep it closed?

-Esta cerrado.

-It's closed? It's done? OK, cool.

All right, I'm ... scared now.

-Thank you.

-OK?

This gaffer tape, this is OK on the suit?

-No problem.

-No problem?

-OK.

-OK.

Dallas, are you OK?

I'm good, I'm fine.

'You are ready to go.'

Oh, my God, this is scary.

Good luck!

OK, we're just about at the surface of the water.

OK, here we go!

My God, it's completely black.

Pitch black, but hopefully, with a torch you can see

the horrors that are beneath here.

Just bits of food floating about, God knows what.

You know, when you pull the chain

you're not really expecting to see it again.

Ah, look at that, it's just disgusting.

OK, so Julio's going to go and fix the pump.

And we're going to be his side-buddy.

I've got the other end of the rope, and I'm going to hold the rope.

I can just feel, just poo beneath my feet.

20 million people's worth of poo beneath me.

What is that?

Oh, my God, look at this, look at this.

This is the kind of stuff you find in the sewage.

I can't believe someone's actually thrown away a horse.

That's why Julio's job is so important.

Things like this clogging up the pump.

-A trophy!

-OK.

-I'll put this on my wall!

Que sus impresiones?

Oh, my God, the stink!

'Unblocking a mega-city's sewer by hand isn't just disgusting,

'it's also impractical.'

There's about 110 miles of sewer system here in Mexico City

and only two guys...

..to keep the whole thing unblocked.

It really is just a sticking plaster solution.

This is tequila?

Salute.

Salud.

Buena leche!

-Ah, that's good.

-Hmm?

-That is good!

-Thank you very much!

-You're my hero.

Mexico City's problem is growing worse as it continues to expand.

Julio and his dive team are the old-world solution.

Mexico City is entering a new age.

Whether you're fixing up your house

or you are in charge of an entire mega-city,

as every builder will tell you,

eventually, you have to get your drains sorted out properly.

And this is something Mexico City is coming to terms with.

This is the world's biggest sewer and wastewater pipe.

It's seven metres in diameter, and when it's finished, it's going

to be 39 miles long and capable of being able to get rid of

150 cubic metres of water per second.

That's the equivalent of 150,000 people flushing their loo,

all at the same time.

Six tunnel-boring machines are digging, day and night.

It's a carefully choreographed process that leaves behind

75 metres of brand new pipe every day.

This machine is much more than just a digger.

It's a tunnel-making factory.

As it moves through the earth,

concrete sections are bolted into place, sealing the walls.

Leaving behind a finished, watertight tunnel.

The ironic thing about this tunnel

is that it's actually rather beautiful, you know.

It's dramatic, it's aesthetically satisfying,

it's meticulously constructed.

But no-one's ever, ever going to see it, apart from you guys, obviously.

You know, they're going to have an opening ceremony,

and they're going to cut the red ribbon,

and the only thing that's going to come through here is you-know-what!

Right across the globe, over 300 huge machines are tunnelling

beneath our feet, transforming the world we live in.

Under the Swiss Alps, the world's longest tunnel

will create a new artery to keep Europe on the move.

In London, the vast Crossrail project is tunnelling

from east to west, to move millions of people across the capital.

And beneath New York, the largest construction project

in the city's history is modernizing its water supply.

From the inside out, we're redesigning our planet

to cope with its ever-expanding population.

This is Cleo, and she came into the world on June 6th at 10:08.

This is Ellis Louis Marie,

and he was born early hours of Monday the 4th of June.

This is Jaden Grusset, and he was born on the 3rd of June.

He doesn't have a name yet, but he was born at 3:30 this morning.

Can't even begin to fathom what she's going to be.

Maybe an astronaut.

I hope he takes after me, like, into drama and music and dancing.

Save the world, maybe.

Go and be a Greenpeace conservationist,

that would be quite cool.

Oh, my God! Well, if his dad and his brother are anything to go by,

probably a racing-car driver.

Or his brother wants to be a ninja.

All babies are special, but one new arrival

could be very, very special indeed.

This little fellow was actually born yesterday,

which was also the day that the United Nations declared

that the human population has hit seven billion.

So I suppose this little guy has got as much claim

as any other baby anywhere else in the world who was born yesterday

to be number seven billion.

But what I find amazing is that since my birth,

the population has doubled.

We've never seen such a dramatic population explosion in our history.

Let me try and put a population of seven billion into perspective.

If you wanted to count to seven billion out loud

it would take you more than 200 years.

It's been an estimated that one in 20 of all the people ever born

are alive right now.

Engineering a world that's fit for so many of us

has called for some pretty quick changes.

One country's speed of transformation

leaves everywhere else standing.

Hello, ni hao! How are you? Thank you, thank you.

If you were going to count which of the world's skylines

had the most cranes, or where the bulk of the world's concrete

was being poured, or follow one of the biggest, fastest

human migrations in history, all roads lead to China.

Welcome to Shanghai, one of China's largest cities.

Its skyline is vast, dramatic, futuristic,

and it's been built almost from scratch over the last 20 years.

China's mass migration from the countryside to the city

began 30 years ago.

Now, every week, 10,000 people make Shanghai their new home.

To accommodate all those new arrivals,

the city has been building at breakneck pace.

One man has a very special record of the changes to his home town.

'When Yao Jianliang started taking photographs,

'he had no idea he was producing a unique document.'

Wow, what a view. How often do you come up here to take photographs?

Can I have a look? At your photos.

-Can I see them?

-OK.

So this is this exact area, this is right here. OK.

There we go. 1990, nothing there at all.

That's just completely flat. From 1990 to now,

I mean, you can see, it's just extraordinary, isn't it?

You know, the terrifying thing that I've just realized is that

I've got DIY projects in my house that have taken longer

than it's taken Shanghai to build an entire city.

These photos are a unique record of just how fast human beings

can change the world if they put their minds to it.

Their minds, and a couple of 100,000 builders, obviously.

This accelerated change is now happening all over China.

In the next ten years, around 350 million people

are expected to head into its cities.

That's almost six times the population of the UK

looking for a new home.

To accommodate everyone they'll need to build at lightning speed.

One company in Southern China says it can build a 30-storey building

from start to finish in less than three weeks.

This is like doing flat-packed furniture at home,

but this is just much larger scale.

This building will be finished in 15 days. That's all we need.

Their secret is to prefabricate as much as possible

in their factory beforehand.

So this is the floor unit.

It contains the wiring, the air conditioning, the water supply,

and the fire protection.

So everything is fitted here to save time.

Once delivered to the site, it's a race against time

to link all the flat-pack sections together.

200 engineers work day and night in rolling shifts.

Another night, another floor!

After seven days, the Chinese team have completed 18 storeys,

about 60 metres of finished building.

As well as being built at incredible speed,

it's also designed to withstand a magnitude nine earthquake.

It is an extraordinary achievement.

In just over a couple of weeks, they've erected a building

capable of housing more than 1,000 people.

China is relying on innovative engineering like this.

It has to, when migration into its cities is so rapid.

Around 100 new tower blocks are needed every week,

just to keep up.

Across the planet a vast migration is taking place.

Hundreds of thousands of us arrive in the world's cities every day,

and they're groaning under the strain.

Half of the population of Caracas now live in slums.

In Mumbai, over six million of the city's population

are crammed into barely 6% of its living space.

And in Lagos, 70% of the residents

make up one of the largest slums on the planet.

In our new urban world, there are now over one billion squatters.

This is Earth's biggest construction project.

Well, at least part of it. And this is Uberajara, the man behind it.

Now, it may not look much at the moment,

but people like him are laying more bricks,

they're pouring more concrete,

building more houses than any place on Earth,

and if you look around here,

these are actually the cities of the future.

Here in Brazil, slums are known as favelas.

Rio alone has over 700 of them, home to up to 1.5 million people.

That's about double the population of Leeds, crammed into slums.

This is Daniella.

She's eight months pregnant and the reason for this project.

Her family have been slowly extending this house

for four generations.

It was Daniella's great-grandfather who laid the first bricks

in this house, and as time went by and the family expanded,

future generations built more and more rooms.

Thousands of families extend their homes in this way,

and it's this chaotic approach to urban planning

that makes districts like this so cramped and overcrowded.

Slums or shanty towns, favelas, whatever you want to call them,

wherever you are in the world, they get a lot of bad press.

But the city of Rio, cleverly, has realised, actually,

you're never going to eradicate them.

The best way to deal with them is to embrace them.

And a central part of their plan is passing above my head right now.

Rio has built the most extensive urban cable car system in the world.

And it's had a profound effect on the residents of the favelas.

Where they used to be isolated from the rest of the city,

now the cable car lets them fly above the chaotic streets below.

It is a genius solution, isn't it?

Suddenly, all the people who live deep in the favela there

have quick and easy access to the rest of the city,

something that they just didn't have before.

It's an investment the city hopes will transform people's lives.

OK, I'm going to try a little experiment just to show you

how much things have changed.

This is Hamaris and Romerio.

I'm going to go to that yellow cable car station over there

using the actual cable car itself.

And these two guys are going to run at ground level

over there as fast as they can.

Are you ready? Three, two, one, run!

Here we go.

Of course, I've got the easy option. The boys' journey

is a baffling labyrinth of narrow streets and endless steps.

You can see just how densely populated all the houses are.

There's absolutely no way you could drive in between the houses,

let alone set up a bus system or a tram system or anything like that.

And travelling on foot means being careful to avoid crime hotspots.

The great thing about this gondola system

is that the stations themselves, they've got a police station,

they've got a health centre, a community centre.

They have become these integral parts of the entire community.

The houses are so tightly packed together,

engineers had to lay the cables painstakingly across the rooftops,

before raising them to a height of over 30 metres.

OK, so that is about, what?

Three-and-a-half minutes from that station to this station,

something like that. Wonder how my pals are getting on.

The cable car has only been open since July 2011

and it's already transforming this area.

Thriving property market.

Our local friendly estate agent tells us, nine months ago, 10 grand.

Post cable-car, 30 grand.

But they'll take an offer.

Darkness falls and there's still no sign of the boys.

In fairness, sunset's pretty rapid in this part of the world.

Still, they have been gone for more than an hour.

You made it!

Very good! Very good! Well done! Well done!

The cable car represents a brighter future for this area.

And who knows?

One day, this favela may become a sought-after place to live.

But if you think that's an impossible dream,

then look what happened somewhere a little closer to home.

This is one of London's trendiest spots,

and it's kind of a good example, actually, of how cities

can radically change over time.

This was one of the worst slums in all of London,

one of the worst slums in all of Europe.

Now look at it.

This is Notting Hill in London, famous for a film, a carnival

and astronomical house prices.

It's quite a lot, £1,600 a week.

If I wanted to buy it, what would that house be worth now?

Probably looking at about 2.5 million.

See, that's ridiculous.

You've got Holland Park Tube two minutes away,

the park itself is five minutes away.

There's a roof terrace on the top, there's open-plan living,

there's modern bathrooms.

It's a good kind of fashionable area, community feel,

it's really nice.

-Two million, can I get it for that?

-Nope.

-Seriously?

-Yep, most things go for asking price around here.

But that's not how Charles Dickens saw it.

I've got my own particulars here,

-this is the same description of the same street but from 1850.

-OK.

OK, so this was when Charles Dickens was writing

and sort of chronicling the area.

"There are foul ditches, open sewers,

"defective drains, smelling most offensively

"and generating large quantities of poisonous gases."

"Stagnant water is found at every turn,

"not a drop of clean water can be obtained.

"All is charged to saturation with putrescent matter."

-Grotty.

-Sounds disgusting!

And you're trying to charge me 2.5 million for the house!

You can't... I mean look at it, it's in black...

There's Charles Dickens! Anyway. I'll take it!

Not every slum is going to turn into Notting Hill,

but the moral of the story is cities do change,

because they have to.

Our population has exploded,

and the modern urban world is taking up the strain.

This is Tokyo, the biggest city the world has ever seen.

In little more than a generation, it's trebled in size.

It's an intricate man-made landscape,

covering an area eight times the size of London.

A generation ago, a city of this scale

would have been inconceivable.

But in the future, there will be more cities of over 30 million.

And we've already seen a glimpse of what they may look like.

'Super-tall buildings will make the most of the space above ground...

'..and giant tunnelling machines will open up the earth below.'

Hello!

'With human ingenuity,

'our ability to redesign the planet is almost limitless.'

I think that this is up there with any natural landscape.

But cities aren't just about buildings and boxes

and roads and railways.

They're about something much more important.

Ultimately, they are about us.

As a species, we seem to thrive living together in our millions.

We've become an urban animal and we've chosen a future

that will have a man-made world at its heart.

Subtitles by Red Bee Media Ltd