Something new is happening on planet Earth,
big enough to be seen from space.
Hot spots, buzzing with the energy of millions of people.
For the first time in human history, more of us live in cities than in the country.
But these are cities on a different scale.
In just 50 years, we've seen the birth, the growth
and now the dominance of the megacity.
Sprawling, seething, noisy, polluted,
crammed with 10 million, 15, sometimes even 30 million people.
These cities are complicated, fragile places,
constantly on the edge.
These are places of overcrowded squalor.
But these are also the most exciting places on the earth.
Brim with optimism and fun and energy.
Hey! HE GRUNTS
Love them or loathe them, fear them or embrace them,
the megacities are the human future of the planet.
We have, at the last count,
created 21 of these extraordinary urban sprawls.
Pulsing and beating entities, giant organisms in their own right.
And these cities and our experience of them
is shaped by how we move around them.
Total chaos! I would call it anarchy,
but that would be extremely unfair on anarchists.
In this film, I'm going to be asking how our megacities can survive
without having a colossal heart attack.
Motorways, the freeways, the railways below us
are the veins and the arteries.
But all round the world, these arteries are getting clogged up and congested.
They're gobbling ever more resources...
That's some cow!
..and dumping grotesque amounts of waste.
So, how does the metropolis deal with all the stuff its people don't want?
Solid fat!
Now I want to wipe my nose but, on the whole, I think I won't.
And what length do people go to
to stop the modern metropolis from drowning in its own excess?
It's unimaginable, what he's just lowered himself into.
Why are our great cities where they are
and why are they the shape they are?
All around the world,
you see the same pattern.
Coastlines and river mouths.
And there's no mystery
in why the great cities love to dangle their feet in the water.
Because throughout history,
sea lanes and rivers were the original superhighways
and even today, it's transport - that basic need to get in and out -
that shapes and stretches
and sometimes even strangles the cities of the world.
How to move millions of people around a megacity 24 hours a day,
without bringing the place to a shuddering halt
and without literally choking its citizens to death,
is one of the major challenges we will face in the 21st century.
I'm starting this journey in one of the poorest,
most chaotic and overcrowded cities of them all -
Dhaka in Bangladesh.
There's simply no money for fancy subways or slick freeways here.
And with a population of 13 million, and rising, to shunt around,
Dhaka is feeling the squeeze.
People still have to move around. Whatever it takes.
And it's hot, intense and rather dangerous.
Every great city depends entirely on its transport system.
But if there's one choke point all round the world, it's the morning rush hour,
when millions upon millions of people
struggle to get to their jobs
and, seemingly, will do almost anything to make it in.
The megacities are the most extreme example of this,
and the poorer ones the most extreme of the extreme.
There are so many people trying to move around this dense city
that it feels like there isn't a rush hour, because the entire day is one massive rush hour.
A rush day.
With just two train lines to serve a population the same size as London's,
and only one major highway,
the result is predictable mayhem.
So, how can you get around a city of 13 million people effectively?
Actually, it's using one of the most primitive modes of modern transport,
pedal power.
Because Dhaka is the rickshaw capital of the world.
Noisy, stinking, slow
and extremely dangerous.
CAR HORNS BEEP
But for most people around the world
this is the reality of urban transport,
not some dinky high-speed train.
There are well over half a million rickshaws in downtown Dhaka,
that's roughly one for every 20 people.
Hardly surprising, then, that 80 percent of all male newcomers to Dhaka
start out as one of these human taxis.
They work ten hours a day, seven days a week,
pulling some seriously heavy loads.
And so, as a new arrival, I think it only right I should have a go.
Now, I'm a keen cyclist in London, so how hard can this really be?
MAN SPEAKS BENGALI
TRANSLATION: It isn't the traffic. He's saying it's difficult to ride in a...
Straight line? Yeah. Yeah.
What are the most important rules of the street?
TRANSLATOR SPEAKS BENGALI
The brake is the most important thing. The brake's the most important thing, OK.
Is it as easy as riding a bike?
THEY CHATTER IN BENGALI
I think that means it's not as easy as riding a bike!
Here I go.
HE LAUGHS
Hey! HE GRUNTS
CHILDREN CHEER
Apparently, there are 600,000 of these in the city.
And I'm beginning to get a sense
of how much human horsepower
it takes to move Dhaka around.
I'm supposed to keep to the left, but it's so crowded here
I'm being forced into the middle of the road.
And with a cab on the back, it's difficult to judge exactly how tight a gap I can squeeze through.
Oh, my God! Oh, I'm sorry.
Oh, I'm sorry.
What you soon realise is, you can never get up a good head of steam.
You're constantly stopping and starting.
And it's far harder and much more exhausting than it looks.
That was both great fun and really, really hard work.
More difficult than it seems.
I had a great time doing it for about 20 minutes, but I think that's about my lot.
These guys do it for, what, ten hours at a time or more?
It's astonishing.
They're said to be as fit as Olympic athletes
and I have to say, I can well believe it.
Thank you. OK. Thanks, guys.
But Dhaka's reliance on rickshaws
means more than simply back-breaking labour
for tens of thousands of its citizens.
It also affects the shape of the city.
Because if your only means of getting around is by rickshaw,
then you are restricted to travelling fairly short distances.
Which means, in turn,
that Dhaka is one of the most densely-populated metropolises in the world.
If you look at the map of any old city and see how it grows,
you can see that it expands in concentric rings as the transport gets better.
From horses to bicycles,
to cars and trams and trains and metro,
the bigger the rings, the more effective the transport.
There's one very simple truth...
The better the transport, the bigger the city can grow.
And today's megacities have taken that simple truth
and pushed it to the absolute extreme.
London. One of the planet's first great metropolises.
With a population of 13 million, including all its surrounding areas,
this city was built not on roads but on steel.
In the early 19th Century,
London was 30 times smaller than it is today.
With only horsepower to move its people around, it simply couldn't get any bigger.
And then a revolutionary new form of transport started to reshape this great metropolis
and all of Britain's other big cities.
The oldest megacities, like London, were only ever able to gobble up the land around them
thanks to whizzy new technologies like the train.
As the tendrils of train and tram networks spread out from the centre,
the suburbs followed and the population mushroomed.
And just when it looked as if the train companies couldn't demolish any more houses
to build any more lines,
they had another bright idea - to go under the houses instead.
From the opening of the first underground station in 1863,
in just 40 years, the population trebled to six million.
London's roots would become criss-crossed by a web of tunnels,
transporting more than 2.5 million people every day.
It was revolutionary.
And in the 150 years or so since then,
the London Underground has hugely expanded
and been rebuilt and patched up and grown and copied.
But everything has its limits.
The number of people you can squeeze through these tubes
has now reached its maximum.
It's a bit as if you were given one pair of trousers for life
at the age of 12.
You get bigger and bigger
and, first of all, the trousers start to squeeze a little bit
and then it's a really painful squeeze.
Well, this wonderful piece of world-breaking technology
has now become London's painful squeeze.
That is the problem with these arteries of megacities.
Very easily, they become crammed and sclerotic
and they're on the edge of collapse again.
The men who built the London Underground thought they had their city sorted.
Nothing lasts forever.
Success sucks in many more people
until it starts to feel like failure.
That doesn't stop people on the other side of the world trying just the same thing,
though bigger and faster than London.
This is the Shanghai Metro.
20 years ago, Shanghai didn't have an underground at all.
Now it boasts the largest one in the world,
and they've built it at an awesome speed.
TRANSLATION: The total soil excavated after completion of the networks
will be around 22 million tonnes,
including all the soil that needs to be dug out of the stations.
22 million tonnes!
I'm very proud of what we've done.
In the last few years, we've managed to complete the same length of lines
that it's taken 100 years for foreigners to build.
It's a great method of transport.
I'm sure London's engineers were just as confident all that time ago.
But the Chinese Government haven't stopped with a mere subway.
They've spent well over a billion pounds
on a revolutionary new overground train system
known as the Maglev.
These trains, built in Germany, have no wheels.
Using magnetic levitation,
they literally float along the track at extraordinary speeds.
We're doing 380 kilometres an hour.
385. 388. 390.
400 kilometres an hour.
425, six, seven.
431. We're now doing more than 431 kilometres an hour.
I think that's about 270 miles an hour.
This thing is flying.
It makes a British InterCity train look like a horse and cart.
And just as the tubes reshaped London,
it's thought that these super-fast services
will reshape this entire area of China.
It's too soon to say
how Maglev trains might reshape China,
but experts are already talking about giant urban areas
of perhaps 100 million people each.
This is how futuristic transport
can entirely reshape the way we think now about cities.
Then again, I'm not so sure.
People's dreams of futuristic freedom
rarely pan out the way that's expected,
and there's no clearer example of that
than what's become the true curse of the megacity the world over -
the humble car.
And the people of Shanghai are in love with that.
In China, just 25 years ago, private cars were banned.
Now they're joining the roads of Shanghai alone
at the rate of 1,000 every day.
And China has become the largest car market in the world.
Meet Shanghai citizens, Wenbing Wu and his wife Jee Chen.
They've come to the BYD, or Build Your Dream, car showroom in Shanghai
to take a look at a new motor.
This would be the first vehicle that they, or any of their family, have ever owned.
As far as I'm concerned, they have no idea of what they're letting themselves in for.
TRANSLATION: We had to save every month. We've been saving up for a really long time.
Wenbing and Jee are typical of the megacity-dwelling Chinese.
The thing about cars, is that they are just so appealing.
Who would want to sit on a sweaty subway
or cram into a crowded bus when you can cruise in air-conditioned comfort?
For many of us, commuting by public transport
is such a gruelling experience
that getting a private car is a tempting alternative.
But this is about more than just getting from A to B.
It's about status.
Now, in a place like Shanghai,
having a shiny new car of your own shows that you have made it.
For this couple, it's clearly cost them a lot,
but they seem convinced that their new car's going to be worth it.
Now we've managed to get a car, all of my family are really happy about it.
It's like you've realised what you've been dreaming about for so long.
So all of us are really happy.
If only we could take them by the hand and lead them to the streets of...
Mexico City, say.
For this really is a city built on tarmac.
Here there are almost 20 million people
and nearly five million cars.
Traffic here is so heavy
that commuters can spend six hours a day, a third of their waking lives,
sitting in their cars
just trying to get to work.
This is transport not just shaping the megacity,
it's in danger of killing it.
The motorways, the freeways, the railways below us
are the veins and the arteries of any city.
We're in Mexico City, one of the most congested places on the planet.
These arteries are getting clogged up and congested.
And we know what happens if you get too much of that.
You get an urban heart attack.
Mexico City's traffic cops are fighting a war, and they are not winning.
I'm with the police helicopter pilot Captain Oscar Cardenta
to get a whirlybird's-eye-view of the morning commute.
Just 7:30am. Already jams are forming down below,
and they stretch as far as we can see.
Right now, we're going to be coming up on, uh,
on Periferico, which is usually very busy at this time of day.
Mexico City's Periferico is the city's major ring road.
If anything goes wrong here, the police know it will spawn rush-hour hell.
How can you help from the air? I have a traffic specialist
and he's giving orders to the people on the ground
to detour the traffic, control the flow.
It isn't long before Oscar spots trouble.
Something's slowing down the traffic on a critical flyover.
Left unchecked, this could spell gridlock, so he's straight onto it
and a team of motorbike traffic police are despatched.
They're going to need to act quickly
because any hold-ups can degenerate into city-wide chaos.
This time, it just turns out to be a broken-down car.
The young couple driving it have simply run out of petrol.
No hanging around for the AA here.
So dire is the congestion, that in Mexico City
the police have learned to improvise.
Unconventional, but it works.
So if we're all going to live in the megacity, and it rather looks like most of us will,
are we all condemned to a future of choking jams and sweat-packed tube trains?
No, I think that maybe we don't want to turn our backs on our low-tech past.
Maybe Dhaka and its half a million cycle rickshaws
does have something to teach us.
Across the globe
and London is gearing up for a three-speed revolution.
To get real change in the city, you need two things.
You need pent-up demand on the streets and you need proper leadership.
When the two come together, change can happen very, very fast.
A good example would be the London bicycle scheme.
When this got going...
..a lot of people said, "It's not going to work,"
and within the first ten weeks there were a million journeys made.
# I seen you riding around The streets at night
# On your bicycle #
There's no single magic bullet that's going to solve the megacity transport crisis.
We have to snaffle ideas from all over the place,
taking smaller, smarter solutions
which, when you take them together, can have an impact.
London's first large-scale public bike-hire scheme
is part of that potential mix.
In the economy of the great cities,
they're always learning and copying and stealing from each other.
And it's not just from the hi-tech cities.
So Dhaka in Bangladesh may be a nightmare,
but it's a nightmare run on pedal power
and that's something that modern cities are re-learning.
And so to have a transport system that really works you need everything.
You need the taxis and the cars and the buses.
You need the trains and you need bicycles
and, of course, decent places to be able to walk safely, as well.
It's a bit like fusion food, you know, that we eat all the time.
You bring in all sorts of lessons, all sorts of flavours
and you mix them up
and with a bit of luck and leadership,
you get a city that's moving again.
This is an example of how the megacity can function at its best.
A bit of technological innovation, some risk,
fingers crossed, and openness to what's worked elsewhere.
And what goes for transport
goes for what is transported, as well.
And not just people.
Moving all of those commuters around,
that's just one layer of the amazing web of activity.
Because these people need to be clothed and fed
and kept warm and watered,
and that means that the megacity's routes
stretch far beyond the ordinary city boundaries,
to far-off generators providing the electricity
or distant mountain reservoirs providing the piped water.
But the greatest appetite is, of course, for food.
The megacities are monstrous hungry.
24 hours a day, seven days a week,
they suck in an astonishing array of food.
Flown, shipped and driven in from all round the world,
and we expect it served how, when and where we want it.
London is no exception. It's one very hungry and thirsty megacity.
Every year, London eats seven million tonnes of food
and downs 94 million litres of bottled water alone.
London's total food footprint is 125 times its size.
In other words, it requires the equivalent of the entire productive land of mainland Britain
to feed London.
Such is the megacity's demand for fresh food,
we're forced to grow it on an increasingly industrial scale.
Even the humble lettuce gets the treatment.
This farm produces over 60 million lettuces every year.
And to do that, it takes a well-drilled small army of pickers.
Plants get lifted, and then creeping just behind is a machine
with yet more workers bagging and packing.
Within another 24 to 48 hours, they'll have been whisked down a motorway,
unloaded, sorted, packed, loaded up again,
and now they're in your fridge perhaps.
Or they might end up here, in one of the strangest supermarkets I've ever been to.
It is supersized.
It looks like an ordinary supermarket, but it plainly isn't.
The aisles are too big, the trolleys in those aisles are too big
and the people doing the picking are all dressed in uniforms.
Because the food that they're choosing, they're not going to take home and eat.
They're not going to wash with the shampoo that they're selecting
or drink the drinks they're taking off the shelves.
They are buying for online shoppers
and they're being told what to pick and how to pick it by a computer.
So right now, to help feed the megacity, welcome to the mega supermarket.
The shelves of this unique London Tesco online store
groan with 22,500 items,
spread over the equivalent of three football pitches.
There are no bright and shiny signs enticing you to buy here,
just series of numbers and codes guiding the pickers.
When we pick, we have to pick by location.
OK. So pick by location first...
It's the numbers of the aisles you're looking for? Yes.
So you're looking for 61. Yeah. D2. Right.
Almond milk. Almond?
That's the one. That's the one. That's the one.
Sharon and her fellow workers end up picking a total of 1,800 orders every day.
That's like shopping 600,000 times for groceries a year.
Quite a lot, it's a battle with the clock
to juggle up to six separate customer orders at one go.
They've all booked their delivery slots.
And how quick do you have to be normally, when you're not surrounded by people like me?
Erm, we've got a time bar at the bottom
that tells us how quickly we're going.
At the moment, it's red and... You're not going fast enough? No.
I'm well out of time.
So they're possibly waiting for me, but...
So there's a specific van waiting for you? Yeah.
Being ordered around by a computer might make this a seemingly alienating job,
but I'm reassured there is a personal touch, however small.
So, what happens if you get to your number
and what they want isn't there?
We have to put a substitution in.
I mean, like, I've substituted this morning, erm, red wine.
They wanted Cabernet Sauvignon. Yeah. I substituted it with Shiraz.
Right. Shiraz is better anyway!
The megacity says, "Make it bigger, do it faster."
These people are presumably shopping online
because their own lives are so stressed and under the cosh,
they haven't got time to shop for themselves.
The result is that they produce a whole other group of people
who are also rushing around, shopping against the clock.
But it's a curious business. What you choose to put in your mouth
or put down your throat or clean yourself with,
these are intimate decisions
and we rely if not on the kindness of strangers
then the choice of strangers.
The honesty of strangers. The hard work of strangers.
Of course, all this consumption inevitably has a consequence.
Our modern megacities spew out huge quantities of waste.
Every year, London throws away 20 million tonnes of the stuff.
Trying to cope with just some of the deluge
is causing a massive strain for megacities.
An astonishing 40,000 miles of sewers
lurk beneath Greater London.
Uncoiled and laid end-to-end,
they'd stretch twice around the world.
But the original sewer system, a Victorian labyrinth of 450 miles of interconnecting tunnels,
still serves the city above.
And just like that other Victorian innovation, the London Underground,
the sewers are struggling to cope.
The arteries of the megacity are clogging up.
I came into television to start with because I was looking for glamour.
HE LAUGHS Now you've got it!
'Rob Smith's one of 39 flushers
'who maintain Central London's sewer network, and they do it the old-fashioned way - by hand.'
Are you ready to go then? Ready to go. Come this way.
Here we go.
Here it is.
It smells exactly as you expect. I don't have to describe it.
The Victorian sewer system was built when London was a mere toddler of a megacity,
home to only 2.5 million people.
150 years later, it has to deal with the end product of at least ten million.
The biggest headache for Rob and the small army of flushers
is not just what all those millions eat,
but what it's cooked in, too.
Wow.
HE CHUCKLES
Yeah. So, that's fat? That's fat.
Where does it come from?
About a couple of miles up in that direction.
We've got Leicester Square, Trafalgar Square.
So, is this fat from restaurants and kebab shops and so on?
Exactly. Yeah. Yeah, that's where it comes from.
So when we talk about, you know, you eat too much fat, too many burgers and chips,
your arteries get furred up... Same with the sewers.
This is London's arteries getting furred up with fat. That's right.
It's astonishing and very, very disgusting, as well!
I suppose we'd better go and take a closer look.
I think we ought to now we're down here.
WATER GUSHES
That is truly foul.
Really hard. That's old fat, that.
Oh, right. We'll go back up the top. Back up again? Yeah.
There we go. That's the product of our fast-food burger-eating,
chip-eating, kebab-eating lifestyle.
Solid fat.
Choking up the sewers underneath London.
Now I want to wipe my nose but, on the whole,
I think I won't.
Across the globe, the consequences of the waste crisis in Mexico City
are on an epic and al fresco scale compared to London's sewers.
This is what's known as the Grand Canal.
No gondolas, no palazzos and no tourists either.
It's a hundred-mile-long open sewer,
designed to transport waste water to the central sewage works.
I fear it is time for me to experience sewer cleaning
on an altogether different level.
I'm told that at this moment,
clever people are working on a form of television that you can actually smell.
And all I can say is, be very glad they haven't got there yet!
The reek here is unbelievable.
These canals were designed 100 years ago
to handle the run-off from Mexico City's rainy season.
But their history has been overtaken.
The modern mania for casually throwing things away
reaches its inevitable consequence here.
Clogged and festering, almost everything gets tossed in here.
And the truth is, we are becalmed on a sea of plastic,
dead dogs - there's one just there - and much worse.
I am, quite literally, up a certain creek
with a paddle, which is doing me no good.
I won't give you the statistics about how much excrement the average human produces each year,
you don't want to know, except that it's lots,
or as the scientists would say, lots and lots.
And so a city the size of this one, with nearly 20 million people,
produces the equivalent of an Olympic swimming pool-full of excrement every minute,
and something has to happen to it.
But blockages can't be got rid of from the relative safety of a boat, or with a spade,
as in London's ancient sewers.
This calls for someone with a diver's license, a cool head and a very strong stomach.
When it comes to unclogging, Ricardo Vazquez is the go-to guy.
Is it dangerous, what you're doing now?
HE SPEAKS SPANISH
TRANSLATION: It's dangerous because of all the pollution in the water. Also because of the glass and nails.
Is there anything you wish you hadn't found?
Dead bodies.
Two or three every year.
I hope you have a good day today. I hope it's not too bad.
I should say that Health and Safety
have insisted that I can't go down there.
And I think, for the first time in my life, I'm thinking, "Go Health and Safety!"
Once he's submerged, the only contact Ricardo will have with the outside world
is via a radio in his suit.
His suit is the only thing between him and the highly toxic broth.
That's one of the most bizarre things I've ever seen. I mean...
It's unimaginable, what he's just lowered himself into.
With glass, nails, sewage
and maybe even the odd decomposing animal to contend with, it's a risky operation.
Ricardo now has to dive to the bottom of the tank
and clear out the filters.
Down there, I'm told it's completely pitch black.
So you can't see anything at all.
What you know is that horrible things are blocking up the system.
And if they're allowed to keep blocking it up,
the entire sewage system starts to malfunction.
There's a metre of just solid trash at this bottom of this, as well, so there's no ground, if you like.
After five minutes, a radio message comes from the deep.
He's found a tree.
While still submerged, working by touch alone,
Ricardo sets about dislodging the offending tree.
I can't think of somebody who is more useful to the people of Mexico City
than the man who's just gone down there.
Blockage dealt with,
Ricardo's winched out for a shower and a strong dose of disinfectant.
The size of the megacity food-and-waste footprint
threatens the future of the planet.
But the metropolis has always been a great engine for innovation and radical change.
And the solutions aren't all top-down or about civil engineering.
They can start off deceptively small and simple.
Cooking oil.
In every city in the world,
this stuff is as common as cigarette butts and beer cans. It's everywhere.
Megacities produce millions of gallons of it all the time
and it's normally seen as a problem.
You've seen what happens when you stick it down drains and that is not pretty.
But imagine if it was, in fact, liquid gold.
An answer to transport problems.
It's a pretty weird idea,
but often, salvation...
is in the detail.
This restaurant has signed up to a pioneering scheme
that takes all their waste oil, which would simply get poured away, adding to London's sewer blockages,
and transforms it into something useful.
And it's all thanks to this man.
Every day, Nigel Jewison and his team do their restaurant round,
picking up drums of dirty, used oil.
But the HQ for Operation Cooking Oil is here,
down in the heart of old London.
Crammed in among the grimy railway arches,
this mini refinery is a magnet for London's cabbies.
Hundreds of them queue here every week to get their fill.
You can see the lovely quality of that oil. That's, er...
And this is how we like it. Classy restaurant, classy oil.
That's not always the case, though. There's a few restaurants I won't eat at, even with their good names,
after seeing their waste oil.
So this is a very straightforward filtration system.
Dirty oil becomes less dirty oil,
sits in these tanks and becomes clean-ish oil,
and then, eventually, clean oil.
At which point, it can be made into fuel for the taxis.
Hiya, Pete. How's it going? Busy on the streets? It's OK. It could be better!
It always can. Always better. Hello there. Hiya.
Have you been doing it for a while, using the biodiesel?
Is it good for you, as a taxi driver? Fantastic. Why?
It's cheaper, for a start. It's cleaner. Yeah.
With the new legislation coming on the older cabs, it could be a way to get us to last a bit longer.
Do you notice the lack of black smoke and smells?
Definitely. But because it smells of fish and chips, you're always hungry!
If you go to classier restaurants, it would smell of garlic and all sorts of stuff. Garlicky cabs.
One of my dreams when I first started up, when people started talking about smells,
was that, if I could collect all the Chinese restaurants, on another round, Indian restaurants,
we could open up a filling station with Chinese-smelling fuel, Indian-smelling fuel.
So you could choose your nationality of fuel!
It'd be brilliant, wouldn't it?
But it's good news for you guys. I think it's very good. It's a shame they can't put it in buses. Yes.
Coming to the amount of cooking oil in the city centre, around London,
how widespread could this be in fuelling taxis, fuelling cars?
If we can collect all the oil in London, we could probably fuel all the taxis,
which would be a fantastic thing. Amazing. It would be.
If a great city like London had to rely on the elected politicians and the planners for its solutions,
I think it would be a much less interesting and more constipated sort of place.
Very often, the big ideas are found
in the little nooks and side streets of the city.
And the job of the politicians is to get hold of those ideas
and, using their taxes and their rules,
to ensure that they then spread and seed much more widely.
Putting old cooking oil to good use is one thing,
but what about all the other stuff we chuck away without a thought?
Well, that ends up here, in a landfill site.
London is near to the bottom of the European cities landfill league,
only recycling about 25 percent of its waste.
And it's running out of space to dump its growing, growling
mountains of rubbish.
The truth is that we in the West throw away far too much.
I do. You probably do, as well.
And when we think about it, we may feel a bit guilty.
And increasingly, we're being kind of mildly bullied
by councils and government to throw away less.
But when you come to a place like this,
you realise why.
Perhaps we do have to learn from those parts of the world
where they recycle everything they possibly can.
In Dhaka, it isn't a case of recycling with a conscience.
This is the extreme end and it's driven by necessity.
Here, entire communities are completely reliant on salvaging the scraps,
the megacity's leftovers,
to carve out some kind of living.
It's sort of like when a large animal is killed in the jungle
and the carcass is picked completely.
And this is an urban version of the same thing.
Rather than microbes doing the picking, it's little boys.
Dhaka's main rubbish dump is the size of a small town,
and a town with its own people.
Here, anything that can be melted down or reshaped and reused
is bagged up and carted off to be resold.
And when I say anything, I really do mean anything.
What are you looking for?
TRANSLATOR SPEAKS BENGALI
Plates, cartons, bottles. Plastic... Plastic. I can understand that.
And what does she do with them when she's got them?
SHE SPEAKS BENGALI
TRANSLATION: Takes it to the shops and sell it.
Everything there is scrunched and dirty.
These are not bottles that could ordinarily be recycled.
This is absolutely the leavings of the leavings, the scraps of the scraps,
the final pickings
after everybody else further up the food chain
has taken what's worth something.
Here, even the insidious plastic shopping bag is given another life,
melted down and recycled.
In a sort of most unpleasant way, I suppose,
poverty is very efficient.
Everything is used.
This might seem like a rather hardcore solution
to the waste problem of the metropolis,
but perhaps the Dhaka necessity for re-use and recycling
has lessons for us at home.
The longer all of us live in the city, the more disconnected we get.
More of our food is processed and pre-packaged.
It arrives in cartons and little plastic boxes.
And instead of being sure about when something has gone off
and it's no longer acceptable,
we rely on those rather timid sell-by dates.
"If in doubt, chuck it out."
Which is a wasteful way of living and of eating.
Dinner with Simon and Fran,
another pair of metropolis innovators.
They call themselves freegans.
There's bread here. That's £1.30 for that.
£1.30 that'd cost in the shop. It's good bakery bread. Nothing wrong with that at all.
Large whites.
Can you find a date on there? The 16th. That's yesterday.
Bread doesn't just go off overnight.
What are these? Diet Pepsi.
I'll just pass them to you. There's a lot of it.
You'll be belching for a week! Yeah!
It makes me feel gaseous and horrible!
Just look at this!
Twice a week for the past two years, Simon and Fran have sifted through the skips
of the back of London's high-street stores and they've yet to go hungry.
Apart from the fact that it's good news for you, does it make you angry?
It does. Because of the waste.
Because there's people in the world who are starving, and we have an abundance and we throw it away.
What's that? Hold on a minute.
What have you got? Ha-ha! Chocolates. Chocolate. OK.
Not bad.
Why would that be thrown away? I have no idea. What's the...?
February. Chocolates don't just go off.
'I don't generally make a habit of routing through rubbish bins, and it does feel a little odd.
'Legally speaking, however, what's thrown away is fair game.'
And so to the getaway vehicle! THEY LAUGH
What's the range of stuff that you're picking up?
Meats. A lot of meat that we find. Yeah. Cheese. Milk.
Yoghurts. Yoghurts.
What would you say to people who say, "It's past its best-by date?"
Use your common sense and have a look at it.
Best-by date, obviously it's saying, "If you want it perfect, eat it before then."
But, you know, the food's still perfectly edible.
Have you ever been unable to feed yourselves
by freegan... lifting of stuff out of bins?
Not in London. No.
There's too much abundance and waste to not be able to do it. Yeah.
Simon and Fran's fight against the waste footprint is only half the battle.
Managing to work out how to supply a metropolis with all the resources it needs
requires an equally smart way of thinking.
Food often travels thousands of miles before it arrives on our plates.
It's inefficient, it's wasteful.
But to find a solution, perhaps we need to travel back in time.
Away, at last, from the madness of the megacity.
Birdsong, nature... Back in the countryside.
Except that I'm not in the countryside.
I am inside Mexico City
and we're on our way to see its famous floating farms.
They go right the way back as an idea to the original Aztec city,
which was built on a lake.
And the way they fed themselves was, the created little floating islands,
and on those islands, they grew the plants they needed to eat.
In the 16th century, Mexico City, or Tenochtitlan,
was the largest city in the world.
The Aztecs' floating islands, or farms, were vast rafts
made out of reeds, fertilised with mud from the lake, and organic waste.
The result was highly productive. An amazing two-thirds of the city's food
was grown within the city limits.
DOG BARKS
Now we're in the 21st century,
one of the questions is, could we go right the way back?
Could we learn to grow more of our own food actually inside the city?
Pedro Castillo is keeping traditions alive
from before the Spanish Conquest.
It's a beautiful. Claro.
His fertile little holding of vegetables
is home to livestock and an abundance of fruit and vegetables,
which are all sold back to downtown Mexico City
a couple of miles away.
Why did they start to grow the food on the island?
And is it a good way of growing food, to have a floating farm?
HE SPEAKS SPANISH
TRANSLATION: It was more about necessity.
It was the lack of space, the lack of room to cultivate their crops that brought them here.
And then they noticed it was very good for farming.
So, you yourself, what do you grow here and where do you sell what you grow?
They grow lettuce, spinach, tomato,
corn, radish.
< HE SPEAKS SPANISH
Normally, they sell it in the market here in Xochimilco,
but right now, they're selling to very selective restaurants in Mexico City. Very good.
Pedro makes a mean tamale, that's a kind of corn dough served in leaves.
Mm. Very good.
And like all good farmers, Pedro does a nice line in home brew, as well.
This is a traditional tipple which is made out of cactus sap.
It's got a kind of caramel taste. And it would be extremely rude not to sample it properly.
It is damn fine!
Mm! Very good. HE SPEAKS SPANISH
TRANSLATION: You're offering it to the mother earth.
Of course, this is very much a Mexico City story.
You don't get tamales and floating farms most places.
But perhaps there's a lesson here.
Because although they're built by humans,
cities depend on nature.
We're inside nature, we're part of nature.
And the great cities that we build thrive or die
because of the natural world around them.
We tear up the past and we ignore nature at our peril.
Just like Mexico City, London used to grow a substantial amount of its own food
within a few short miles of the centre.
This fertile farmland, known as the breadbasket of London,
is better known today as Heathrow Airport,
where food, very often similar food,
now arrives from South America, Africa, Asia.
I'm not saying we should rip up and plough what we've built over,
but we do need to be more clever about how we use what we've got.
If the future shape of metropolis seems to be ever more dense and increasingly high rise,
then, maybe, some of the answers to feeding the city have to be urban ones.
For decades, people have imagined a science-fiction future.
A vertical city and farms in the sky.
It's not entirely far-fetched.
Architects are already hard at work.
Nearer to hand, inside this inner-city London terrace,
the seeds of something pretty big could be growing.
Like most ground-breaking ideas, they start small.
This is a mini hydroponic and aquaponic farm.
There is no soil here. The plants are grown under light, in mineral solutions and water,
fertilised by fish droppings.
Fresh eggs are laid daily in a rooftop coop.
I'm under no illusion that a few salad plants and hens are going to solve the food crisis,
but think how much neglected space London has to offer
a whole city of potential 21st century urban farmers.
Farmers like Paul Smith.
Our big plan is to grow food all around the city,
in warehouses, empty buildings and old derelict spaces.
When you're growing inside a building,
the best way to make use of the space is to grow upwards, create vertical installations,
layers of food within buildings.
This a movement happening all around the world that we hope to be part of.
We're trying to demonstrate you can get the best of both worlds.
You can have an ecological food system in the city,
and if you do that, we'll have a much lower food footprint for everybody.
If we can get enough people growing food in cities, it'll be one part of the picture.
The city has an absolute, in our view, critical role
in fulfilling the future food needs of a place like London.
Over the next century, disasters permitting,
the growth of the megacities will stretch onwards.
In the last hour, in the time that it's taken to watch this programme,
7,500 people have moved from the country to a big city.
In that hour, the world's slum population has gone up by 3,000 people.
Shanghai's underground, already the longest in the world,
will have grown by a further five metres.
And so is the inexorable rise and the dominance of the megacity
a cause for despair or hope?
There's no single answer to any of this.
We need the planners. We need the Shanghai-sized ambitions.
But we also need the kick from the streets.
We need the stroppy cyclists, the backyard innovators,
and the idealistic freegans trying new ways of living.
Because cities don't belong to the town hall or the architects or the commissars.
Cities belong to citizens.
Are they going to be new urban nightmares
or are they going to be places where we dream new dreams and bring them into effect?
Well, that's up to me. And you.
Subtitles by Red Bee Media Ltd
E-mail subtitling@bbc.co.uk