All language subtitles for BBC.Horizon.2009.How.Many.People.Can.Live.on.Planet.Earth.PDTV.XviD.AC3.MVGroup.org.eng

This is the Earth, our planet.

Home to millions
of different species.

But only one species
dominates everything.

Human beings.

There are nearly seven billion of us
living on the Earth.

And the human population
is increasing by more than
two people every second.

200,000 people every day.

Nearly 80 million people every year.

Each additional life
needs food, energy, water, shelter

and hopefully a whole lot more.

Today we're living in an era

in which the biggest threat to
human wellbeing, to other species,

and to the Earth as we know it,
might well be ourselves.

The issue of population size
is always controversial

because it touches on the most
personal decisions we make.

But we ignore it at our peril.

There's absolutely no doubt at all
that the world's population
will continue to grow.

The only question is by how much.

More than a billion people
on the planet already lack access
to safe, clean drinking water.

And we know things are going to
get more difficult as the population
continues to grow.

We need to double the amount of
food that we have available to us
as soon as possible.

Such a scale of change
will leave no-one untouched.

Keep in mind that when the Titanic
sank, the first-class cabins

went to the bottom
just as quickly as the steerage.

I was born into a world of
just under two billion people.

Today there are
nearly seven billion of us.

Whenever I hear those numbers I can
honestly say I find it incredible.

Triple the number of human beings in
what seems like the blink of an eye,

and the world transformed utterly.

Human population density is a factor

in every environmental problem
I've ever encountered,

from urban sprawl
to urban overcrowding,

disappearing tropical forests
to ugly sinks of plastic waste.

And now the relentless increase
of atmospheric pollution.

I've spent much of the last 50 years
seeking wilderness,

filming animals
in their natural habitat
and to some extent avoiding humans.

But over the years, true wilderness
has become harder to find.

I can't pretend that
I got involved with filming
the natural world 50 years ago

because I had some great banner
to carry about conservation.
Not at all.

I've always had huge pleasure
in just watching the natural world
and seeing what happens.

I made those films because it was
a hugely enjoyable thing to do.

But as I went on making them,
it became more and more apparent

that the creatures
which were giving me so much joy

were under threat.

The fun is in
delighting in the animals.

But if you do that
you owe them something,

and so you have an obligation
to speak out

and do what you can
to help protect them.

I support a group called
the Optimum Population Trust

which campaigns
to reduce birth rates.

Because I think
if we keep on going,

we're not only going to
damage nature,

we're likely to see more and more
inequality and human suffering.

In this programme
I want to see how population growth

will affect our ability to obtain
our most basic needs -

water, food, and energy.

And to see if it's possible to
answer the question,

how many people
can live on Planet Earth?

Human beings
are good at many things.

But thinking about
our species as a whole
is not one of our strong points.

I don't even think I could
tell you how many people
live in this country.

A googol?
Yeah, I would say a googol.

TRANSLATION: I know India's
population is 1.1 billion

but I don't know the population
of the world.

I'd say six billion
off the top of my head.

TRANSLATION: I've got no idea
how many people live
on the planet, no idea!

Luckily, the size of the human
population is studied very closely.

By and large, every human birth
and death throughout the world

has been recorded
for the last 60 years.

The data is kept here in New York
City, at the United Nations.

Hania Zlotnik, head of the
UN Population Division, is in charge
of those precious numbers.

This was the old type of working,
when I arrived at the UN.

I worked with these types of files.

They are very well-organised
but they look old.

Now we do it via computer
and it's somehow not the same thing
as feeling the data.

I am a numbers person,
yes, definitely.

'My mission is to be
the bean counter.'

That means we are the thermometer
telling you

that the planet is getting hot or
cold in terms of population change.

The UN do much more
than just keep records.

They make projections
into the future.

And their figures are staggering.

The human population
is still growing.

One expects that at the very least
it's likely to add

about 2.3 billion people
by middle of the century.

We have 6.8 billion today.

We're expecting to get
the seventh billion
in the next three to four years.

And then that by mid-century we'll
have something like nine billion.

In the next 40 years, the Earth
will need to accommodate

nearly three billion more people.

That's more than the current
population of the whole of Europe,

the whole of Africa,
North and South America combined.

How can we be so sure of
this prediction?

Well, we know that there are more
than a billion teenagers alive today

and most of those teenagers
will have children of their own

and live long enough
to become grandparents.

And that's all that needs to happen

for there to be nine billion
humans alive in 2050.

It's not people
having huge families.

It's just a lot of people
doing what humans naturally do.

We also have a good idea of where
these additional people will live.

There are likely to be
ten million more people in Britain.

100 million more in the USA.

India will overtake China
to become the most populous
country in the world.

The population of some countries
will shrink -

Japan, Russia, Germany,
and much of Eastern Europe.

The places that will experience
the most rapid growth

are also the least developed
countries in the world.

Afghanistan's population
will double.

Most of Sub-Saharan Africa
will double.

Niger's population is predicted
to more than triple.

I think everyone living through
the next 50 years is going to be

affected by these demographic
changes, wherever they are.

For most of human existence,
our population size

was kept in check by nature,
just as it is for other animals.

If there's plenty of water,
food and materials for shelter,

a population will thrive.

But when disease, famine or drought
strike, life can be cut short.

The history of humanity
is one of overcoming
these environmental limits,

but it took us
a very long time to achieve.

On the horizontal axis here we have
time over the last 10,000 years.

On the vertical axis here we have

the size of the human population
in billions of people.

Over the last 10,000 years,

in general there's been
very little change.

It's a very boring picture.

But from about the year 1800 onwards
you have a major increase,

a very large increase
in the world's population

from about 1 billion
up to 7 billion today.

Basically what this increase
in population represents
is control of death rates.

Death rates have been reduced
because infectious diseases -

cholera, smallpox, malaria, measles,
those sorts of things -

have been massively reduced.

On average for almost all of
human history, a man and a woman

were only survived into adulthood
by two of their children

and that's why the world's
human population didn't increase.

Extending life
by controlling disease

is perhaps one of the greatest
achievements of humanity.

I was born into a world of
2.5 billion

and I'm seeing it almost triple
in my lifetime.

And life has not gotten worse.

In fact for most of the population
of the world,

life has gotten better
in these 50 years.

Living healthily and long has
consequences - population growth.

Just as the human population
was starting its unprecedented
growth spurt

in the late 18th century,
this was published.

It's a first edition of
An Essay on Population

by the English clergyman
Thomas Malthus.

Malthus made a very simple
observation about the relationship

between humans and resources
and used it to look into the future.

He pointed out that "the power of
population is indefinitely greater

"than the power in the Earth
to produce subsistence for man."

Food production can't increase
as rapidly as human reproduction.

Demand will eventually
outstrip supply.

Malthus goes on to say,
if we don't control
human reproduction voluntarily,

life could end in misery,
which earned him a reputation
as a bit of a pessimist.

But Malthus's principle
remains true.

The productive capacity of
the Earth has physical limits

and those limits
will ultimately determine how many
human beings it can support.

To help answer that question,
we need to have an idea
of what human beings need.

And the people who calculate this
more precisely than most

are the people
who are more interested in leaving
the planet than staying on it.

Astronauts.

One of the people in charge of
the wellbeing of astronauts

on the International Space Station
is Doug Hamilton.

NASA, we calculate
and simulate everything.

If you are going to plan a rocket
launch, you have to know how much

food and water and equipment
you need to bring into space.

As well as working out how much
space the astronauts need,

Doug and his team have to calculate
their daily requirements

for food, water and breathable air.

They typically need about 820 grams
of oxygen, which is

just a really large,
large balloon, really.

We need about 4,000 to 5,000
calories of food

which is about 820 grams dry,

and they need about 3.52 litres
of water,

of which 2.5 litres
is just consumed daily.

We want them to drink a lot of
water - it's very good for them.

And then we urinate out and put that
into our processing system
and we make it into drinkable water,

so you might be drinking
the same water molecule
hundreds and hundreds of times

on the space station,
because we recycle.

NASA's calculations
are tailored for space,

but they're the same ingredients
each and every one of us needs.

When you see how hard it is
to reproduce

what Mother Nature
does every day for all of us,

you begin to really appreciate
the world that you have.

Whatever our
technological achievements,

we're still utterly reliant
on the natural systems of
the Earth for our very survival.

By and large the planet has provided
for the human race, so far.

As the population has increased,
people, through agriculture
and industry,

have exploited those resources
ever more effectively.

But increasingly,
we're seeing signs of strain.

We're reaching the limits
of our environment.

Perhaps most alarmingly
with that fundamental ingredient
for life - water.

We call our Earth the Blue Planet

because about 70% of the Earth's
surface is covered in water.

But most of that is sea -
just 2.5% is fresh water.

And of that tiny fraction,
just 1% is available for human use.

The rest is locked up
in mountain glaciers

and the Earth's polar ice caps.

But there's another fact
we need to understand about water.

Well, there's no more water
on the planet than there was
when life first appeared on Earth.

It changes its distribution.

There's more water in different
parts of the world.

But its still the same amount of
water that's been here always.

We appropriate over half of
all the available fresh water
in the world to serve our needs.

To transform deserts into fields.

To generate energy from rivers.

And to build cities in some of
the most arid regions on the planet.

But despite our ingenuity,
there are many who struggle to
get enough of this basic resource.

More than a billion people on
the planet already lack access to
safe, clean, drinking water.

And we know that things are
going to get more difficult
as the population continues to grow.

Within the next 20 years as much as
half of the world's population
will live in areas of water stress.

Chronic water shortages are often
the result of poor infrastructure,

politics, poverty, or simply
living in an arid part of the world.

But increasingly the pressures
of population are to blame.

Mexico City is ranked as the
eighth-richest city in the world,

ahead of Moscow, Hong Kong
and Washington DC.

It also benefits from
heavy annual rainfall.

But its water system
is buckling under the pressure

of supplying water
to its 20 million inhabitants.

And every day
at least a million people
are affected by the shortages.

Enrique Vazquez is a water
truck driver for the government.

And the number of people relying on
this emergency service
is growing daily.

Today he's heading for a poor
district in the city's south-west,
where he's a regular visitor.

TRANSLATION: At some time in
the future, wars are going to
be fought over water, not oil.

But people don't seem to understand.

Instead of conserving it,
we just waste it.

The problem is a combination of
leaks in the system,

and back-up reservoirs
that are running dry.

The city authorities predict
that these reservoirs

may be completely emptied
within a matter of months.

TRANSLATION: Look - the tap's on
but there's no water coming out.

The people living here
have had to adapt their lifestyles
to an erratic water supply.

We only have half a bucket of water
to wash ourselves with.

And we can't flush the toilet until
two or three people have used it.

TRANSLATION: Unfortunately, I think
there's going to be water shortages

all over the world,
not just in Mexico City.

I think everyone needs to
take water more seriously.

The few people who have water
should conserve it better,

or there'll come a time
when the shortages are global,

and there's little left for anyone.

In Mexico City, shops which sell
water to meet people's daily needs

are becoming ever more common.

But the water we use at home
is only a fraction of the water
we actually consume.

And that's because
we use colossal quantities
in industry and agriculture.

We may know where the water
out of our tap comes from,

but we seldom know where the water
that went into our can of cola

or into the shirt we're wearing,

where those goods were produced
and how much water it required,

what the consequences were
for the natural systems

and local communities that
are dependant on that same water.

So for example the cup of coffee
you may have in the morning

requires on the order of 120 litres

just to produce the coffee
and bring it to your table.

A can of beer, 150 litres.

A hamburger, 8,000 litres of water.

To produce enough water
to grow the cotton in my shirt

is 3,000 litres, as well.

The impact of human demands
on the world's freshwater systems

are so massive,
they can be seen from space.

The Aral Sea, a freshwater lake
in Central Asia,

once covered 65,000
square kilometres.

In the last 40 years
it has lost 90% of its water,

the rivers that feed it
diverted to irrigate cotton.

Lake Chad on the southern edge
of the Sahara

has also been drained
to a tenth of its former size

by drought and overuse.
Yet 30 million people depend on it.

It is possible to distil
fresh water from the sea.

And in the last 20 years,
more and more countries
have turned to desalination.

But with current technology
desalination plants

are often extremely expensive,
use an enormous amount of energy

and their by-products
can be damaging to our seas.

With groundwater levels
declining across the world
from North Africa to China,

Pollution of rivers and wetlands
on the increase,

and already today
more than 1.2 billion people
living with water scarcity,

our prospects for providing water
to nearly three billion more people
do not look good.

But in many ways, supplying water to
people is the least of our worries.

As we've seen,
the lion's share of the water
we use goes into agriculture.

And that means any water shortages
we face in the future

will affect our ability to provide
that other staple of life - food.

When it comes to the world's
food supply,

some of the most accurate
information comes from space.

Geographer Molly Brown
monitors food production on Earth

using data from NASA's satellites.

This is a ecosystem in Thailand,
where they do rice agriculture,

and it's extraordinarily productive

and in one of the most highly
productive agricultural regions.

Now she's beginning to see global
agriculture hit a natural limit.

One of the things that all these
different landscapes really show us

is how we're using almost
all the land that's available to us

that's really highly productive,

that has great
agricultural potential. So we know

that there isn't
a lot of extra land.

I mean, we're using 30 or 40%
of the entire land surface.

As the world's population increases,

the urgency with which we're
going to have to increase the amount
of food we produce will increase.

So we need to double the amount of
food that we have available to us,
as soon as possible.

How we're going to do that
is through raising productivity,

because there's really no more land
with which to expand to.

A doubling of productivity
sounds ambitious,

but we've done even better than that
in the past.

In the 20th century,
the industrialised nations managed
to triple their farming yields

with the invention of
synthetic fertilisers

and then by the introduction
of mechanised processes.

The less developed parts
of the world continued using
traditional farming methods

into the 1960s,
until an Iowan farmer

decided to do something about it.

Norman Borlaug, who died this year
aged 95,

is credited with saving millions
of lives in what's become known
as the Green Revolution.

So he was a very unpretentious man.

You can see from his office.

Small but very functional.

And he had some of his awards
on the wall.

But also, in particular,
I always thought this picture

which he kept on the wall
was quite typical of

the kind of person he was.

His interactions with
the next generation of scientists

around the world and his enthusiasm
for getting out into the field

and showing people what could be
done with the science,

in improving agricultural
productivity.

Borlaug developed high-yielding,
disease-resistant crops

and taught Indian
and Mexican farmers

how to get the most out of them
with modern farming methods.

The astonishing five-fold increases
in yield that they achieved

allowed many countries
to become self-sufficient in food.

In 1970, Borlaug received
the Nobel Peace Prize

for his work
in alleviating world hunger.

He was able to get his wheat, his
new varieties, delivered to India,

and within a few years,
it was really astounding.

He showed me pictures of
the mounds of wheat,

the surplus that had been produced
within a few years of
introducing these new varieties.

And in fact that's the seminal
event, that's the Green Revolution.

Thanks in part to Borlaug,
much of the world is now fed,

but globally we're beginning to see
a levelling off
of agricultural yields.

This is leading to
a worrying new trend.

To maintain their own food supplies,

some of the richest and most
powerful countries in the world

are acquiring large tracts of land
from some of the very poorest.

Olivier De Schutter
is a human rights lawyer

who's been monitoring these
land deals for the United Nations.

Arable land suitable for cultivation
is becoming a scarce commodity

and countries
find it more and more difficult

to produce enough food
to feed their populations.

So they are now scrambling
in a global competition

to achieve food security
by buying land abroad.

International corporations
and increasingly governments

are leasing some of
the last remaining areas

of un-developed farmland
in the world.

Their aim is to introduce
intensive farming methods

and export the food
back to their home countries.

The problem is that in most cases

these deals are not
sufficiently well monitored.

They are not transparent, and we are
not certain that local communities
will benefit from these investments.

These deals are often controversial
and shrouded in secrecy.

But according to
local media reports,

Chinese investors
are negotiating land deals

throughout Africa, as well as with
Kazakhstan, Mexico and Brazil.

Saudi Arabian firms
have leased farmland in Sudan.

And several British investment funds
are reported to be raising capital

to buy farmland
in Angola, Malawi and Ukraine.

Most of the target countries
for foreign investors are in Africa,

some of which already struggle
to feed their own people.

When we see paradoxical situations

such as foreign investors
producing food in Ethiopia,

shipping this food
back to the home country,

or selling it
on the international markets

when Ethiopia is still a country
which is heavily dependent
on international food aid.

So this is a country which is
at the same time producing food
for export markets

and depending on international aid
in order to feed its population.

The future is going to be
particularly challenging for
the countries of sub-Saharan Africa.

With many of their populations
projected to double,

there's going to be
increasing pressure
for a limited supply of land.

There are few nations
as acutely aware of

how destabilising these kinds of
pressures can be as Rwanda.

Our land is not growing

and yet our population is.

We estimate that it will be double
in 26 years,

so in 26 years
we will probably be 20 million.

Rwandans consider land
a vital resource.

But they also see it as a resource
for primarily their own use,

for their own security,
for their own food security.

Martin Seturinka grows bananas and
maize on three acres of farmland.

Like 80% of Rwandans, his family
subsist on what they can grow.

Land is an issue all over Rwanda.

There isn't enough land
to go around

and people find it hard to grow
enough food to survive.

In Rwanda, children inherit land
from their parents,

but in a country where the average
family has more than five children,

that can only mean one thing.

Smaller parcels of land to live off.

I don't know
what will happen to my children,

or how they'll cope,
I honestly don't.

It's already impossible for me
to provide enough food for them.

Only God knows.

Martin is father to 15 children.

But they aren't all his own.

Five of them are adopted,
orphans whose parents

were brutally murdered
in Rwanda's devastating genocide.

In 1994,
the two major tribes in Rwanda,

the Hutus and Tutsis,
embarked on a mutual slaughter

that left almost a million dead
in just three months.

Amongst the many causes
of that conflict,

competition for scarce resources
was an added pressure.

Poverty became a mobilising tool,
the poor unemployed youth,

some of them were encouraged
to kill their neighbours...

..with the hope they'd either
inherit their piece of land,

or their house,
or their livestock.

If we cannot grow the economy
fast enough to meet this growth,

and can't slow it down, then there
will be increased competition

for resources which are finite.

So our forests are likely to go,
our swamps will be overused.

Therefore this will also
have an effect on the climate,

climatic changes
which will further exacerbate

the negative effects
of this growth.

It's a bit of a vicious cycle and
we must find a way of breaking it.

In Rwanda, the government
can already foresee the impact

population growth is likely to have
on their immediate environment.

Across the world,
population growth is likely to take

an even greater toll because of
our ever-increasing demands

for a resource
we've come to depend on,

but which may be causing us
the biggest damage of all.

Of all the resources that humans
have harnessed from the Earth,

the one that has transformed
everything is energy.

Fossil fuels are the remains
of plants and animals

that lived perhaps
350 million years ago

and later became buried
in the Earth's crust.

With the technologies
of the industrial age,

we liberated this energy

and used it to get more from nature
than had ever been possible before.

Our favourite fossil fuel is oil.

Our demand for it
increases every year.

Today we use
85 million barrels a day.

Oil provides the fertiliser,
pesticide and mechanisation that has

allowed us so far to produce enough
food for our expanding population.

But just as we're realising
how much we depend on it,

it's getting harder to find.

Houston, Texas.

One of the richest places
in the world,

thanks to its vast reserves
of oil and gas.

Danny Davis
is an independent oil producer.

This is our office, our base of
operations and what we do.

Our little company sign,
which we're very proud of.

Danny has been drilling oil
in Texas since the early 1980s.

This is a collection of jars
of oil from all the wells

we've found over the years,
I guess over the last 15 years.

One of them I kind of like the most,

is this one. This was
discovered about 30 minutes

outside of Houston
on the Brookshire Dome.

This came out at 1,000 barrels
of oil a day from 2500 feet.

High gravity sweet crude.
It smells great.

When it comes out its so fresh
you can put it on your salad,

little oil and vinegar,
it's good stuff.

This is why we do it,
this is what it's all about,

it's an exciting business.

There's a fortune to be made
treating these reservoirs.

These days, oil in Texas
is getting harder to find.

Danny's looking much
further afield, to Alaska.

He's been granted a rare license
from the government

to drill offshore.
But before he can get started,

Danny needs to raise millions
of dollars of investment.

Let me ask you a question,
how many years you been doing this,

about 40 or 50?

If his plans are successful,
the figures are truly staggering.

You look at a billion of barrels
of oil and oil's 70 a barrel

and you got two billion barrels,
in gross numbers,

200 billion dollars, probably.

I don't know,
I couldn't predict that.

You can only go on
the value today,

you don't know what
it's is going to be tomorrow.

Yeah, I'll call him and let him know.

Thanks for everything.
All right, guys.

We'll see y'all soon.

Danny won't be short of customers
for his oil because energy demand

is predicted to increase by 40%
over the next two decades.

The Alaskan fields
may make him a very wealthy man.

But the fossil fuels that have
helped to bring great wealth

to many nations
as well as individuals are
proving to be a double-edged sword.

Not just because of their
contribution to climate change.

What cheap energy
has allowed us to do fundamentally

is to appropriate the Earth's
natural systems to serve our needs,

without paying too much attention
to the long-term effects

on the environment
and other species.

It seems we're just beginning
to realise the full impact

that our industrialisation
is having upon the natural world.

In the oceans we've depleted
fish stocks massively.

10% of the world's coral reefs

are estimated to be
degraded beyond recovery.

A third of the world's amphibians,
a fifth of all mammals and 70%

of all plants are currently
under threat of extinction.

When it comes to conserving
our natural world,

there are two arguments
to contend with.

On the one hand, there's a sense
of our moral obligation,

as the most intelligent species
on the planet, to protect

the marvellous variety of species
that have evolved alongside us.

On the other, there's self-interest.
The more we damage the environment,

the more we threaten
our own survival.

Perhaps self-interest
is the more powerful argument

because how we treat our environment
certainly determines

how many people
the Earth can sustain.

There's a concept in ecology
called "carrying capacity".

It's a calculation
of how large a population

any given environment can support.

William Rees is a human ecologist
who's taken the concept

and applied it to ourselves
and our environment, the Earth.

The simple fact of the matter is

the Earth can accommodate
so much consumption.

You might have ten billion people
at one level of living

and a billion at a more comfortable
level of living.

So carrying capacity
is a very flexible idea.

You simply divide the total
productivity of the Earth

by the number of people
and that gives you some idea

of how many people
the Earth can support.

Rees has estimated what he calls

the productive bio-capacity
of the Earth.

This is made up of all the food,
water and energy produced across

the world each year, and measured
in units called global hectares.

He's worked out
that if we were to share the Earth's

productive bio-capacity fairly,
there'd be two global hectares each.

But the reality
tells a very different story.

According to Rees's data,
most of Africa use little more than

half of their share
of the Earth's productive capacity.

The average Indian
uses less than half.

The Chinese use their fair
allocation of two hectares each.

But Europeans use much more
with the British on average

using over five global hectares.

And the average American, using more
than four times their fair share.

So how many people
can the Earth sustain?

Well, according
to these calculations,

if all humans consumed the same
as the average Indian does today,

the Earth could sustain
as many as 15 billion people.

If we consumed as little
as the average Rwandan,

this would go up to 18 billion.

But our planet can only sustain
2.5 billion people

living as we do in Britain.

And only 1.5 billion
living in the lifestyle

of those in the United States.

But the picture
may even be worse than this.

These figures are based
on rates of consumption

that many think
are already unsustainable.

There's plenty of evidence right now

that we are already in the state
of what we call overshoot.

Each year the human population
at current average levels
of consumption,

which most of us in Europe
and North America

would consider to be inadequate,
is already exceeding

the productive capacity
of the planet.

Not only in terms of
its ability to produce,

but also in terms of its capacity
to assimilate our wastes.

Rees believes that today's
population requires the equivalent

of 1.5 Earths to support
our current way of life.

We're simply living beyond the means
of our environment to sustain us.

To have a state of sustainability
where we remain

within the productive
capacity of the planet,

means that people
in industrialised countries

are going to have to give up
consumption of a great deal in order

to create the ecological space for
needed growth in the third world.

If we don't make those kinds
of compromises,

then we're going to continue
to erode the resource base

of the planet to the point
where we all suffer.

As I see it, humanity needs to
reduce its impact on the Earth

urgently and there are
three ways to achieve this.

We can stop consuming
so many resources.

We can change our technology

and we can reduce the growth
of our population.

We probably need to do all three.

For most people, the idea of
someone else telling them

how many children they should have
is simply unacceptable.

So when governments attempt
to do exactly that,

it always causes controversy.

In 1979, the Chinese government
introduced its infamous

one child policy, changing
family life in China forever.

Families were encouraged
to have fewer children,

those that didn't were fined.

The policy was a direct response

to the preceding decades
of famine and starvation.

It's still in place today.

According to official figures,
without the one child policy,

there'd be 400 million
more people in China -

that's more than the entire
population of the USA.

It's unlikely that other governments
could undertake

such an extreme path
without major civil opposition.

In the 1970s,
the Indian government

also sought to
bring down its birth rate.

To start with,
it took a less aggressive path,

setting up festivals
around the country

where vasectomies were offered
in return for small incentives.

In those days, in those festivals,

they have done in a week something
like 80,000 sterilisations.

The incentive was some cash,

some money, nothing much.

The problem was the festivals were
attracting the wrong customers,

people who
already had large families.

That is the weakness of
incentivisation - they could not

attract the couples
with two children,

they attract couples with
five children, six children.

It's like closing the door
after the horse has gone.

But in some areas,
politicians took the sterilisation
drive a step too far.

In 1977, when Indira Gandhi was
introduced the emergency programme.

What they did,

the punishment for every crime
in those days were sterilisation.

For example,
if a person travels in a train,

he has no ticket,

what is the punishment?
He was taken for sterilisation.

In 1977 alone, around eight million
people were sterilised.

And the public outcry was so great

that it helped to bring down
the government.

Hopefully these kind of coercive
policies are a thing of the past.

Because we're beginning to
realise that birth rates fall,

provided the conditions are right.

In the south-west of India lies the
long narrow coastal state of Kerala.

Most of its 32 million inhabitants
live off the land and the ocean,

a rich tropical ecosystem
watered by two monsoons a year.

It's also one of India's
most crowded states.

But the population is stable because
nearly everybody has small families.

How many of you have only one child
in the house? Raise your hands.

Only one. You are the only one
in the house.

Only one? Only one?

I think today almost
30 to 40% of couples

in Kerala have just one child.

How many of you have two
in the house two? Two.

Two in the house.

Today on average, Kerala women
produce only 1.5 children.

How many of you three in the house?

Three, three, three.

No problem, brother or sister?

Two brothers. They wanted a girl.
That's why they got three.
Otherwise no.

You will rarely see a couple with
now three children, very rarely.

At the root of it all is education.

Thanks to a long tradition
of compulsory schooling for boys

and girls, Kerala has one of the
highest literacy rates in the world.

Even too-young children
are coming to school.

See, they are carrying bags
bigger than them.

Where women are well-educated,

they tend to choose
to have smaller families.

When all girls goes to school,

automatically they will marry
very late.

For example, today in Kerala average
woman marries at the age of 28.

Whereas a state like
Uttar Pradesh, Rajasthan, Bihar,

the girl marries at the age of 18.

So, at 28, these women
in Uttar Pradesh and Bihar

have already four children, where
Kerala girl is even not married.

How many children
do you want to have?

ALL: One.

What Kerala shows is that
you don't need aggressive policies

or government incentives
for birth rates to fall.

Everywhere in the world where women
have access to education,

and have the freedom
to run their own lives,

on the whole,
they and their partners

have been choosing to have smaller
families than their parents did.

But reducing birth rates
is very difficult to achieve

without a simple piece of
medical technology - contraception.

We can think of modern contraception
as a crucial technology

for the sustainability of the planet
because it's the element

that has allowed the populations
of many developing countries

to reduce their fertility
as rapidly as they have done.

Despite a recent history that
makes population a particularly
delicate subject in Rwanda,

the government here
is one of the few in Africa

to have made universal access
to contraception

a national priority in recent years.

Console Mukanyarwaya is one of
hundreds of family planning officers

who give contraceptive advice
to local communities.

Since the year 2000,
family planning education

has been provided
for everyone in the country.

Rwandans understand that while
it's wonderful to have children,

you've got to be able to look
after them as well as you can.

We try to get people
who use contraception

to teach their neighbours
so they can see for themselves

the advantages of
having fewer children.

Since it has become
freely available,

the uptake for contraception has
been huge in Rwanda, with many women

opting for injections
or even five-year hormone implants.

While Rwanda is addressing
its population growth,

it's estimated
that a quarter of married women

in sub-Saharan Africa still don't
have any access to contraception.

And across the world, over
80 million births are unplanned.

In my view it's a basic human right,

that everyone should have
access to contraception.

All the evidence is that people
take advantage of this

once they have the possibility
and they reduce their fertility.

If that happens, then, amongst
other things, the world's population

growth will eventually level out at
a lower rather than a higher number.

And that's a good thing.

When it comes to other ways of
reducing human impact on the Earth,

there are a few glimmers of hope
emerging.

Governments across the world
are beginning to recognise

that the life-support services
provided by our ecosystems

are in need of repair, and they're
doing something about it.

Often it takes individuals
with vision

to lead the process of change.

Valente Souza is an urban planner
and a committed environmentalist

with a lot of responsibility.

The government of Mexico City
have employed him to find

a sustainable solution
to their water shortages.

And he's convinced the local
ecosystem holds the answers.

The solution is at hand
and the solution is called the rain.

Because we are at
the top of the mountain

and the only source
of water is rain, not rivers.

We have to re-establish what
we call the hydrological cycle.

This cycle relies on ancient forests
that used to surround the city.

But as the city's grown
they've all but disappeared.

And here you can see
a water truck coming up.

Souza's mission is to protect
the remaining forests.

Part of that is building walls
to prevent soil erosion.

Mexico City is surrounded by a rock
like this with a forest on top.

It rains, the soil
prevents it from running fast.

It trickles inside all of these holes
and the water comes out here,

on the valley of Mexico.

And that's how Mexico City gets
its water from, from this rock,

which is like a doughnut around it.

For this natural process to work, it
relies on a rich layer of topsoil.

My hand is moist,
because this is saturated with water.

If, when it rains, this gets
saturated with water then the rocks

have the time to get saturated
with water, because they have...

They're slower at having
water inside, so you need this.

The only way for us to have water
down there, is to catch it up here.

If we lose the forest,
we lose the water.

Souza is drawing up plans
to conserve,

protect and replant the forests,

working with the local communities
who own them.

These people are the owners
of this particular forest.

It's private property.
And instead of being farmers

cultivating corn,
they cultivate trees.

They call this a water forest.

We're responsible for the forest.
We must look after it.

We make sure there's no
illegal developments or logging.

No pollution, no rubbish.

It's both our role and our duty.

Even in the heart of a vast urban
metropolis like Mexico City,

the intimate relationship
between humans
and the natural world endures.

It seems to me
that an understanding

of the natural world
is crucial for all of us.

After all, we depend upon it for
our food, for the air we breathe,

and some would say,
for our very sanity.

It's a relationship that we're
stretching to breaking point

as we continue to grow in numbers.

Within the course of this programme,

the human population has increased
by another 9,000 people.

Each one of them will be making
their own demands on the Earth.

We have to be using water and all
of the other natural resources

in a much more sustainable fashion.

We have to quit wasting so much,
we have to quit polluting so much,

and if we do those things and if we
put the science and the technology

that's already available to us into
play, into implementation today,

then we have a chance
to make it into the next

30 or 40 or 50 years, and into a
population of eight or nine billion.

But if we don't start doing
those things immediately,

we don't stand a chance.

If current trends unfold the way
some scientists think they will,

it will be a very different planet
by the middle of this century.

The temperature may be up to
two or three degrees warmer.

If that's the case,
food and most other resources

are going to be scarcer.

There will be eight or nine
billion people here

and the question our children
are going to ask us is,

"If you saw this coming, why weren't
you able to do anything about it?"

I'm very aware that this film could
be seen as bleak and depressing.

An increasing population with an
ever-decreasing supply of resources.

But humans have capabilities
that animals don't -

to think rationally,
to study and to plan ahead.

The number of people on the planet
in the future depends on

the personal decisions we each make
about how many children we have.

Even setting aside
the moral responsibility we have

to protect other species, if we
continue to damage our ecosystems,

we damage ourselves.

It's clear that we'll have to
change the way we live

and use our resources.

We're at a crossroads
where we can choose

to cooperate
or carry on regardless.

Can our intelligence save us?

I hope so.

Subtitles by artistharry

E-mail subtitling@bbc.co.uk