Aftermath: Population Zero Page #5

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120 years after humans disappear,

many modern skyscrapers have

collapsed into heaps of rubble.

Concrete walls have been destroyed

by a steady onslaught of air and rain.

But the new landscape has

made cities a little cooler.

When we ruled the planet,

heat from the sun was soaked

up by black roofs and roads.

Asphalt absorbed 95

percent of the sun's light.

Black surfaces made cities up to 10

degrees hotter than surrounding areas.

But now that we're gone,

asphalt is being covered

by grasses and trees.

Shade keeps the ground cool.

The temperature drops.

The world's climate is changing.

Manmade global warming is

finally coming to an end,

thanks to oceans.

For the past 120 years,

churning waves have absorbed carbon

dioxide into the top layers of the seas.

Then, microscopic plankton and

shellfish absorbed it into their bodies.

Many died and sunk to

the bottom of the ocean,

taking our carbon dioxide to the depths.

After the last cars stopped running,

much of their exhaust

is finally being buried.

Our impact on the climate is declining.

The changes are being felt

all around this new world.

In Berlin, young trees attract new life.

The saplings growing out of the

concrete provide food for animals.

But where there are deer,

hunters are sure to follow.

These wolves have come

in from the country.

Most of the wolves in Germany

were killed by humans long ago,

but these hunters are from Poland.

And wolves aren't the

only predators around.

When we disappeared, millions of

domesticated dogs had to fight or die.

At first, the dogs had an

enormous edge in numbers,

but they were facing a

battle they couldn't win.

Many of the newly liberated

pets were neutered.

Unable to reproduce,

they lost their advantage

and slowly died out.

But not all dogs disappeared.

Those that managed to survive

adapted to the new reality

and mated with wolves.

Now they look more

like Australian dingoes,

medium sized with straight

hair and long snouts.

Genetically almost identical,

dogs and wolves were

kept apart by humans.

But in a world without us,

dog and wolf genes are mixing,

assuring the future

of the canine species.

And this new generation

is thriving in cities.

One hundred twenty years

after humans disappear,

thousands of wolves hunt across Europe.

They need to eat every few days, so

they're lured by their prey downtown.

The urban jungle becomes

a new killing ground.

There are some places getting colder

and whiter than when humans were here.

With no black roads or roofs,

some cities definitely suffer the chill.

In northern cities, more

snow falls and stays longer.

But packs of wolves and dogs

still manage to find food

through these cold winters.

South of the freezing

temperatures are rivers,

diverted by humans

for power and commerce.

This is the Thames

River, in London, England.

Humans tried to tame it

for more than 1000 years.

Once, the Thames was a

gateway for thousands of ships.

But its high tides and storm surges

often threatened to flood the city.

So, one of the world's

largest systems of floodgates

was built to hold the waters back.

But without people,

the river is out of control.

Tides have sucked boats into bridges,

creating dams and forcing the

Thames to flow around them.

The banks are flooded.

London returns to the marsh

that the Romans found

here 2000 years ago.

In the American southwest,

the problem is too little water.

This is the Imperial Valley

in Southern California.

Once, it provided half of America's

winter fruit and vegetables.

With 350 days of sunshine,

some crops had four harvests a year.

But only three inches

of rain falls annually.

The dry air helps preserve buildings,

but it's deadly for crops.

People intervened to

make this desert bloom.

Farmers brought in 977

billion gallons of water

each year from the Colorado River,

enough to cover every surrounding

field in six feet of water.

But when we disappeared,

the irrigation stopped.

What was once California's

farming miracle

is now a barren desert.

Another manmade oasis can

be found 300 miles northeast.

Las Vegas.

Built in the middle of a desert,

its casinos and fountains used

water brought in by electric pumps.

When the power went

off, the taps went dry.

Now, with just a few

inches of rain a year,

the desert is reclaiming the city.

But nature hasn't erased

all evidence of our presence.

This is the Colorado River.

It hasn't changed much in the

150 years since we disappeared.

But long ago, it was

much deeper and stronger,

it even helped carve the Grand Canyon.

Today, the Colorado is still

a shadow of its former self.

Dozens of dams were built

to harness its strength

and keep it from reaching

the ocean as a torrent.

Humans also built reservoirs

to contain its massive power.

And there the waters will stay as long

as the dams can hold the river back.

200 years after humans disappear,

nature has taken over

many of the world's cities,

but some rivers are still

shackled by concrete monoliths.

Dozens of dams still hold

back the Colorado River.

The largest of all is the Hoover dam,

just 25 miles from Las Vegas.

It's as tall as a seventy story building

with a base as thick

as two football fields.

Enough concrete was poured to pave a

highway from New York to San Francisco.

By blocking the Colorado River,

the dam created the

reservoir of Lake Mead.

There's enough water here

to bury the state of New York

under a foot of water.

This is the water that once fed the

fountains and swimming pools of Las Vegas.

The Hoover dam is mostly

made of solid concrete.

But even this mammoth

monument is vulnerable.

The reason lies up the Colorado River

near the border of Arizona and Utah.

This is the Glen Canyon dam.

It was created to store water for nearby

cities and to generate electricity.

But this dam has a major weakness:

its spillways,

which act like an overflow

drain on a bathtub.

If the river level gets too high,

the excess water escapes

through the spillway tunnels

so it doesn't go over

the top of the dam.

But the spillways can't

handle sudden floods.

The threat is high in the mountains.

When winter storms produce

unusually high snowfall,

the heavy spring run-off

creates surging floodwaters.

They rush head-on to the dam.

After rusting for two centuries,

the gates that controlled

the spillways have collapsed.

The water races through 700 feet

of tunnels deep inside the dam.

And as it does, it creates

a destructive pattern.

Low-pressure bubbles form in the water.

When they pop, they cause

supersonic explosions that

eat through the rock into the dam.

Once, special concrete ramps

prevented this from happening.

But after 200 years without humans,

erosion has taken over the tunnels.

600 billion cubic feet of water

bursts through the dam

and gushes downstream.

The surge is over 50 feet high.

It sweeps through the Grand

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