National Geographic: Six Degrees Could Change the World

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We have signs of very great

changes occurring on the planet.

Everything happened so fast.

There's creeks drying up that

have never dried up in my lifetime.

We've got a forest here

that's already at the edge.

We're going

into uncharted territory.

Our planet

is at a crossroads.

Global warming isn't out of control,

but it soon could be.

The warning signs are all around us.

This is the challenge

of climate change.

What can we do about global warming?

What will happen

to the Earth if we don't?

The temperature is rising.

Each degree is critical.

Just one degree...

- One degree warmer...

- Two degrees...

- Threshold is about three degrees...

- Three to four degrees of warming...

You're starting

to look at four degrees...

Three degrees,

four degrees, five degrees...

Six degrees is almost unimaginable.

Imagine the 21st century,

if global warming accelerates.

Where does the next super-storm hit,

the next scorching heat wave,

the next catastrophe,

as the world warms degree by degree?

The debate has ended.

Scientists around the globe

agree we now live

in a world warmer by almost

one full degree Celsius.

Tracking the Earth's vital signs

is an armada.

Thousands of ships at sea.

Tens of thousands of stations on land.

Satellites monitoring from space.

Scientists feed the data into

the most advanced computer models

The predictions are alarming.

In four decades,

glaciers in the Himalayas,

the source of water

for millions, could be gone.

Within 50 years,

Greenland's melting ice sheet

could be unstoppable.

By the end of this century,

the Amazon rainforest,

home to half

the world's biodiversity,

could wither to an arid savannah.

A temperature rise between

is possible over the next century.

Each degree means

a radically different future.

Global warming doesn't just mean

the slow increase

in average temperatures.

It completely changes the way

the Earth's system operates,

which is why we can see droughts

in one place, floods in another,

or even a succession of drought

and flood in the same location.

National Geographic

author Mark Lynas

spent years compiling data

from climate models

to understand how each

degree of warming

could threaten the planet.

It's difficult

for people to visualize

the future impacts of global warming.

It's something I really

wanted to try and do,

to help people visualize the reality,

because it isn't actually intuitive

that the emissions

from your car exhaust

are going to be melting a glacier

in the Himalayas in 50 years' time.

While experts estimate

the average temperature

could rise up to six degrees Celsius,

or nearly 11 degrees Fahrenheit,

over the next 100 years,

the future isn't set in stone.

Even a small shift

in the Earth's temperature,

just six degrees,

can have extreme consequences.

Six degrees shift

from one day to the next

is the sort of thing that we expect

with normal weather fluctuations.

If it's six degrees hotter tomorrow,

I might just be wearing some shorts.

Six degrees in terms of a global

average change, six degrees colder,

is the difference between now

and the last ice age,

when the ice sheets themselves

advanced to just

the edge of Oxford,

and in places the ice cap

was more than a mile thick.

Just six degrees of cooling

transformed the Earth into an ice age.

Imagine it six degrees hotter.

The very earliest changes would

start high above the Earth.

The atmosphere

is our buffer zone

between the planet's surface

and outer space.

A small percentage

are the greenhouse gases,

a cocktail of water vapor,

carbon dioxide, methane,

nitrous oxide and ozone.

They are like a dome over the planet,

retaining just enough

of the sun's reflected energy

to maintain temperatures

that support life.

As the amounts of those gases increase,

they trap more heat

and can radically affect

the climate all over the planet.

For the last 250 years,

greenhouse emissions have soared

as we find more and more ways

to use more and more energy.

CO2 is the hidden price we pay.

Carbon dioxide rises

into the atmosphere

from the energy that powers

all our modern conveniences.

It's literally in the air we breathe.

There are now 383 carbon dioxide

molecules out of every million.

It seems minuscule,

but as the amount of CO2 rises,

so does the average temperature

all over the planet.

Doubling of CO2 is

a guarantee for global disaster.

The dangerous level

is about 450 parts per million,

and we're already up to 383.

Additional global warming

of one or two degrees Celsius

is a very big deal.

All we're doing is saying

what we think our best estimate is,

what will happen if we carry on

at the rate we're going.

So what you can do is to lay out

a number of possible pictures

of the future

and hope people will select

the right one.

If the world warms

by one degree,

the Arctic is ice-free

for half the year,

opening the legendary

northwest passage for ships.

Tens of thousands of homes

around the Bay of Bengal are flooding.

Hurricanes begin hitting

the South Atlantic.

Severe droughts in the western U.S.

Cause shortages

in global grain and meat markets.

This could be our world

plus-one degree.

Warming of just one degree

could turn some of America's

most fertile ranchland

into desert... again.

much of the American west

was part of a vast desert

dominating the continent.

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