All language subtitles for Earth.Emergency.2021.1080p.WEB.h264-BAE

We're warming the Earth

and the warming is causing
a further warming.

Most people I know haven't
even heard of feedback loops

or tipping points,

but they are so crucial

to understanding
how the world works.

As we started models
in the late '50s,

we could find the climate
changing in a pretty huge way.

NARRATOR: Scientists
have identified dozens

of feedback loops
already in motion.

Each amplifies warming

and, combined, they are
spinning out of control.

There were places
where we walked

where my foot fell
into the ground

because there was no longer
any ground structure,

because the permafrost
was thawing.

Where we are now, it's like
driving in a car in a dense fog

and you know there's a cliff
out there somewhere,

but you don't know where.

Do you want to be going
60 miles an hour

or should you be going
about ten miles an hour?

NEW SPEAKER:
The Earth will be just fine.

We may take along with us,
unfortunately,

lots of different species.

I'm not worried about the
planet. I'm worried about us.

NARRATOR: If we take action
now, we could slow,

halt or even reverse
the climate crisis

before it's too late.

I'm optimistic by nature
and I become more optimistic

when I see so many people
that realize there's a problem.

We can't allow it
to be too late.

It's time to act.

NARRATOR: If we don't,

the planet will reach
a tipping point

where we will lose the world
as we know it.

Earth is warming...

..caused by the burning
of fossil fuels like oil, coal

and natural gas,
filling the atmosphere

with heat-trapping gases
like carbon dioxide,

methane, nitrous oxide

at levels humans
have never seen before.

As the world debates

how much more warming
the planet can take...

One and a half degrees Celsius?

Two degrees Celsius?

..the climate crisis escalates.

The problems are that the world

is becoming too hot
for the present distribution

of people, agriculture,
human welfare

and human interest,

and it's getting worse.

NARRATOR: But it's more
than our emissions

heating the globe.

Something else is at work here.

The rising temperatures
are setting in motion

Earth's own natural
warming mechanisms

that then feed upon themselves.

George Woodwell,
a distinguished scientist

and a lion
of the environmental movement,

has been sounding the alarm
about them

for the past 50 years.

In a 1989 Scientific American
article,

he wrote that warming
caused by human activity,

"rapid now,
may become even more rapid

"as a result
of the warming itself."

30 years later,
climate activist Greta Thunberg

repeated his warning,

calling them
"irreversible chain reactions".

The popular idea of cutting our
emissions in half in ten years

only gives us a 50% chance
of staying below 1.5 degrees

at the risk of setting off
irreversible chain reactions

beyond human control.

50% may be acceptable to you...

..but those numbers
do not include tipping points,

most feedback loops,

additional warming
hidden by toxic air pollution

or the aspects of equity
and climate justice.

NARRATOR: So, what exactly are
irreversible chain reactions,

what scientists refer to
as feedback loops?

A feedback that everybody
is familiar with

is an audio feedback

where, if you put a microphone
too close to a speaker,

you get this terrible
high-pitched screaming.

And that happens because the
sound comes out of the speaker

and it goes back
into the microphone.

That's called
a positive feedback

because it amplifies the loop.

NARRATOR:
Instead of the guitar,

emissions from fossil fuels
are the input

which add heat-trapping gases
to the atmosphere...

..and setting in motion

self-perpetuating
warming loops -

warming as a result
of the warming itself.

That ever-growing screeching
noise is an apt analogy

for the damage that
human-caused feedback loops

are wreaking on the planet.

Scientists have identified
dozens of feedback loops

already in motion.

It's imperative
that we understand them

if we're going to solve
the climate crisis.

As the climate warms, forests,
once removers of carbon,

release it back
into the atmosphere

as carbon dioxide or CO2.

Frozen ground in
the Northern Hemisphere thaws

and emits CO2 and methane.

The melting of sea ice
in the Arctic Ocean,

increased drought and fires
in the world's forests,

a decay of organic matter

from permafrost thaw
in the Northern Hemisphere

and disruptions
to the jet stream

and our global weather.

These are the kinds
of feedback loops

that lead to further warming,

triggering the release of
even more heat-trapping gases

and raising the temperature
even higher.

Each amplifies warming

and, combined, they are
spinning out of control.

If we take action now,

we could slow, halt
or even reverse them

before it's too late.

If we don't...

..the planet will reach
a tipping point...

..where we will lose the world
as we know it.

With more than seven and a half
billion people on Earth,

a change this great
would spell catastrophe.

Humans are well-suited
to the world we've known.

The sun's radiation passes
through atmospheric gases,

primarily oxygen and nitrogen,
to the Earth's surface.

Some radiation is absorbed
by the planet

and the rest would bounce back
to space

if it weren't
for a tiny percentage of gases

like carbon dioxide, methane,
water vapor and others

that trap heat
and warm the atmosphere.

These heat-trapping
greenhouse gases

make up less than 1%
of the total atmosphere,

but they are essential
in regulating the temperature.

Without them, we would freeze,

but too much of them
would overheat the planet.

Both are possible

and have happened
in Earth's geologic past.

So, the kind of things

that keep climate scientists
awake at night

stem from their familiarity

with the geological record

that shows that the climate is
capable of very abrupt changes.

There are feedbacks
operating in the climate system

that may temporarily go
out of control, if you will,

and drive the climate
to a different state.

We cannot rule out

that we may be in
for such an abrupt change.

We don't fully understand them,

but we worry about that...
a lot.

NARRATOR:
These radical changes

include extreme
temperature swings.

About 500 million years ago,

there was a cycle
of alternations

between a practically
ice-covered planet

and a very hot planet.

NARRATOR: During periods
known as Snowball Earth,

it got so cold,

These alternated
with hothouse climates

when virtually
all the ice melted.

Dinosaurs lived at the poles

where forests
and swamps flourished.

These abrupt shifts were caused

by complex global processes.

This is the first time that
humans have been responsible

for an abrupt change.

Today, Earth would naturally be
in a cooling trend,

but because of human activity,
it's not.

KERRY EMANUEL: So, we know
from paleo proxy records

that the Earth has been
cooling for about 7,000 years.

We recovered from the peak
of the last ice age,

which was
about 22,000 years ago,

it went up
and it's been slowly cooling

until about the time
of the Industrial Revolution.

NARRATOR: At that time,
humans began emitting

vast amounts of carbon dioxide.

Since then,
the atmospheric content of CO2

has gone from 280 parts
per million

to over 400 today

and could approach 800
by the end of the century.

Of all the carbon dioxide
humans emit each year,

oceans absorb about one quarter,

plants take up another quarter

and the other half stays
in the atmosphere,

accumulating over time and
raising Earth's temperature.

But the percentage
nature removes is shrinking

as forests are destroyed
and oceans warm.

Scientists estimate
that doubling CO2

from pre-industrial levels

could produce
an increase in temperature

of up to eight degrees
Fahrenheit...

..resulting in the deaths
of millions of people

and the loss
of countless species.

It's this human-caused warming

that is kicking off Earth's
natural feedback loops

and heating up the planet
further.

National Medal of Science
recipient Warren Washington,

a ground-breaking
climate pioneer,

began creating computer models
in the 1960s

to predict the future
of atmospheric warming

and the role
feedback loops play.

WARREN WASHINGTON:
The question always was,

how do we see

the feedback mechanisms
working realistically?

We really don't know
if we got the right amount

of feedback in our models...

..because they are
so complicated in many cases.

We had to do
a lot of experimenting.

NARRATOR: That experimenting,
coupled with observations,

paid off.

Because of that ground work,

today's models
have more accurately predicted

what our future holds.

This kind of research is crucial

to understanding the policies
we need to implement

to avoid disaster going forward.

Climate policy
really should be designed

to avoid crossing
the important thresholds,

avoid crossing
the important tipping points

and avoid setting off
these important feedbacks

because we need to essentially
ask the question,

how much warming is OK?

Is two degrees OK?
Is one and a half degrees OK?

We really don't know the answer
to that very well.

(BIRDS SINGING)

NARRATOR:
Trees play a vital role

in the health of the planet.

Through photosynthesis,

they help regulate
Earth's temperature

by pulling carbon dioxide,
a powerful heat-trapping gas,

from the atmosphere
and emitting oxygen.

Since carbon dioxide warms
the atmosphere,

by removing it and storing
much of the carbon safely away

in their branches, trunks,
leaves, roots and soils,

forests help cool the Earth.

In fact, every year,

terrestrial ecosystems
remove about 30%

of fossil fuel emissions

and forests are responsible
for most of that.

But that percentage
is decreasing

as emissions increase,

steadily raising
Earth's temperature

and threatening forests'
ability to offset the warming.

We have warmed the Earth by
a full degree and a little more

and forests are suffering
increased hazards of fire

as they get warm and dry...

..increased hazards
of disease...

..as they become vulnerable
to insects...

..and dying as a result.

NARRATOR:
As trees die, they become part

of a dangerous feedback loop
kicked off by the warming.

As the temperature rises,

the climate becomes hotter
and drier

and they fall prey

to drought, fire and insects.

The fewer trees left,

the more heat-trapping gas

remains in the atmosphere,

raising the temperature higher,

resulting in even more dieback.

As trees burn and decay,

the carbon they've locked away
during their lifetime,

what scientists call
a "carbon sink",

is released back into the air.

GEORGE WOODWELL: It's entirely
possible we reach a point

where we're killing off forests
much more rapidly

than carbon can be fixed
by forests.

The net result then
is to produce a feedback

that's lethal.

(BIRDS SINGING)

NARRATOR:
Today, we have a choice -

allow trees to do their job
and cool the planet

or jeopardize the forests
we have.

That's the path
we're on right now.

How we protect
and manage forests

will play a large role
in determining our future.

When it comes to global warming,

three major forests
matter the most -

the tropical, the boreal
and the temperate.

No forest is more critical
for cooling the planet

than the Amazon.

Spanning more
than two million square miles

across nine countries,

this tropical forest has been
storing carbon for millennia,

yet it is dangerously close

to releasing more carbon
than it absorbs.

Mike Coe is the Director
of the Tropics Program

at the Woodwell
Climate Research Center.

For over 20 years,
he has studied

how deforestation
in the Amazon rainforest

affects the local climate
and environment.

MIKE COE: Tropical rainforests
probably account

for about 15 to 20% of all
the terrestrial carbon sink

and the Amazon is half of that.

So, we're talking
about a significant fraction

of our annual emissions
are being taken up

by the Amazon forest.

NARRATOR:
But in the last 50 years,

nearly 20% of this forest
has been lost,

mostly to slash-and-burn
land clearing,

triggering fires, insects
and tree dieback.

This not only releases
the carbon stored there,

it jeopardizes
an important cooling function

of the Amazon rainforest.

During transpiration,

roots pull water
out of the ground

and release it as water vapor

through tiny holes
in the tree's leaves,

creating a cooling effect
on the surrounding air.

In the Amazon, transpiration
can cool the region

by as much
as ten degrees Fahrenheit.

MIKE COE: When we lose trees
in the Amazon,

when we cut them down,
what we're doing

is we're shutting off
that transpiration,

so what you get
is a drier climate.

And the more you deforest,
the drier it gets.

NARRATOR:
Over the past two decades,

the dry season has extended
several weeks,

stressing trees even more...

..and creating
an ideal environment

for fires to spread.

MIKE COE:
During extreme droughts,

a huge amount
of the forest burns.

That turns the forest that year
from a net sink

to a net source of carbon.

We can do the math.

If that happens
five times a decade,

this forest is now a source.

NARRATOR: Today,
tropical forests are absorbing

one-third less carbon

than they did in the 1990s.

Scientists predict that
with the loss of so many trees,

the Amazon could flip
to emitting more carbon

than it stores
as soon as the next decade.

The next major forest
at risk of tipping

from a carbon sink
to a carbon source

is the boreal
encircling the North Pole

through Siberia
and North America.

The largest forested region
in the world,

this vast coniferous expanse

stores an estimated two-thirds
of all forest carbon,

most of it locked away in
frozen plant and animal remains

deep in the ground.

But that's changing.

As with tropical forests,

the warmer, drier climate here

is making the trees
more vulnerable to disease,

insects and fire.

Brendan Rogers has been
studying how boreal forests

respond to climate change
for the past decade.

Wildfires are getting worse
across the boreal zone.

We're seeing more and more
large fire seasons,

record-breaking fire seasons
every year.

NARRATOR:
Unlike in tropical forests,

the fires here strip off
the insulating ground cover,

preventing it from building up
in between the frequent burns.

Without this protective layer,

fires reach further
and further down,

burning the organic matter
stored in the soil.

About 75 to 90%

of all the carbon stored
in these forests is underground

and that is actually
the majority of the carbon

that's getting released
from these fires.

NARRATOR: The fires kick off
a feedback loop,

triggered by warming
in the boreal zone.

More fires burn carbon
deeper down in the soil,

releasing carbon dioxide and
methane into the atmosphere,

heat-trapping gases that make
the climate hotter and drier,

leading to more wildfires.

Like the Amazon, the boreal
forest is going to switch

from a carbon sink
to a carbon source.

Scientists don't know
exactly when,

but predict
that at the current rate,

it will happen
by the end of this century...

..crossing a tipping point

that the forest
can no longer recover from.

The scary thing is not knowing
where that tipping point is.

(DISTANT BIRDS CRY)

NARRATOR:
The temperate forest makes up

only one quarter
of the world's forests,

but it's our best hope

since the tropical and
boreal forests are on the brink

of becoming emitters of carbon.

(BIRDS SINGING)

Once cleared for agriculture,

many temperate forests
in the US and Europe

have made a comeback
in recent decades.

But in the south-eastern US,
old forests are being cut down

by the wood pellet industry
for burning,

releasing decades of stored
carbon back into the air.

Even though these forests
are being replanted,

when it comes to offsetting
global warming,

old and young forests
are not equal.

Beverly Law has been measuring
the exchange

of both carbon dioxide and water

between our forests
and our atmosphere

for the last 25 years.

In a young forest ecosystem,

there aren't
that many trees there

and they're not taking up much
carbon from the atmosphere.

An older forest has
a lot of carbon stored

compared to a younger forest.

If I were to try and mitigate
climate change,

my best strategy is
when you have forests

that have low vulnerability
to climate change in the future

and they store
a lot of carbon already

is to keep those forests
like they are, preserve them.

NARRATOR:
When a tree is logged,

one half to two thirds
of the carbon it stores

is released through decay

or burning of the unused
branches, leaves and roots,

as well as
from the surrounding soil.

Today, 17% of global
carbon emissions each year

can be attributed to logging

and burning wood pellets
for bioenergy.

BEVERLY LAW: In Oregon,

of all the forest harvested
over the past 100 years,

65% of that carbon has gone
back to the atmosphere.

This is just the wrong time
for that in terms of climate.

NARRATOR:
With the clock ticking,

it comes down to how we manage
temperate forests -

use them for commercial purposes

or keep them intact
to cool the planet.

If we decide that we really
are going to stabilize

or even cool the Earth,

we will have to rebuild forests
around the world.

NARRATOR:
In the Northern Hemisphere,

nearly one quarter of the land
is covered

by an icy expanse
called permafrost.

Extending from the surface
down thousands of feet,

its soil contains
billions of tonnes

of carbon-rich plant
and animal remains,

suspended
in a perpetually frozen state.

But now, with human activity
warming the Arctic

two to three times faster
than the rest of the globe,

this permafrost
is starting to thaw.

And alarmingly, it contains
twice as much carbon

as in the atmosphere today...

..and three times as much

as in all the world's forests
combined.

As it thaws, microscopic
animals called microbes

that have been frozen for up to
tens of thousands of years

are waking up

and feeding on the newly thawed
carbon remains,

emitting dangerous
heat-trapping gases.

If we were to take
all of the microbes on Earth,

we'd find that they'd weigh
probably 50 times more

than all of the animals
on Earth.

Now, these microbes need to eat

and what they eat are the dead
remains of plants and animals.

And as a by-product
of feeding on that material,

they produce carbon dioxide
and methane.

It's like having a chicken
in your freezer,

you take the chicken out,
you put it on the counter

and it starts to thaw.

Then you go away for the weekend

and you forgot about
the chicken on the counter,

you come back
and the house smells,

the chicken's decomposed.

That's what happens to the
carbon that's in permafrost.

It's fuel for microbes.

And as they're breaking it down
and using that fuel,

they're releasing
greenhouse gases,

carbon dioxide and methane,
into the atmosphere.

NARRATOR:
Driven by fossil fuel emissions

raising the temperature
in the Arctic,

these microbes are amplifying
the warming

as the permafrost thaws

by releasing
more carbon dioxide and methane

into the atmosphere

and warming the climate
even more

in a self-perpetuating loop.

Which of these
heat-trapping gases is released

depends on the environment

in which microbes digest
the carbon.

In oxygen-rich conditions
like soil and lake surfaces,

microbes produce carbon dioxide
as a by-product.

But in environments
lacking oxygen

like bogs
and muddy lake bottoms,

they produce methane

which is nearly 30 times
more potent

at trapping heat
than carbon dioxide.

The amount of carbon
that could be released

from thawing permafrost
by the end of this century

has been estimated to be up to
150 billion tonnes of carbon.

So, to put that in context,
the US is currently

the second largest
greenhouse gas emitting country

in the world.

If we took
our current US emissions

and added that up through 2100,

this is on par
with the amount of carbon

that might be released
from thawing permafrost.

NARRATOR:
Last summer, while working

in her usual field location
in Alaska,

Natali witnessed
a remarkable acceleration

of permafrost melting.

SUE NATALI: First of all,
it was very, very warm.

It was 90 degrees Fahrenheit
in the tundra.

There were places
where we walked

where my foot fell
into the ground

because there was no longer
any ground structure,

because the permafrost
was thawing.

I've never seen change
happening that quickly

from one year to the next.

NARRATOR:
The thawing permafrost

can entirely transform
the landscape,

as Natali has seen
in Duvanny Yar, Russia.

SUE NATALI: I had never seen
permafrost thaw

and ground collapse
of that magnitude.

You see these really,
really fine roots

that have been frozen
for 40,000 years.

Once they're thawed,
they'll decompose in a year.

NARRATOR: And something else
is having a dramatic effect

on the landscape in Siberia -

crater-like holes which are
thought to be the result

of a build-up of methane
under a thick layer of ice.

When the ice melts,
the pressure gives way,

causing an explosion.

A year or two later,
the craters form lakes

that release
the previously buried methane

into the atmosphere.

Sometimes lakes that form
from shifts in the landscape

emit so much methane,

you can light them on fire.

As the permafrost thaws

and the Arctic heats up faster
than the rest of the planet,

that blanket of warming mixes
into the atmosphere,

encircles the globe

and it leads to all kinds
of global disasters.

Crop failure in the Midwest.

Droughts and flooding in Africa.

Record heatwaves in India.

And in the Northern Hemisphere,

home to most
of the world's lakes,

the warming is having an impact
similar to the permafrost thaw

by bringing new food sources to
the microbes that live there.

Plant species
from south of this region

are migrating north, setting
off another feedback loop.

ANDREW TANENTZAP:
Traditionally, the pine needles

that the microbes
would be digesting

would have provided
quite a limited diversity

of food sources,

but now with deciduous
broad-leaf species

like maple and oak,

that's bringing a much greater
diversity of organic matter

and carbon
for microbes to digest.

NARRATOR:
More food choices means

an increase
in microbial activity

which, in muddy lake bottoms
lacking oxygen,

leads to methane production,
a warmer climate

and more greening of lakes

in an ever-amplifying loop.

And the geographical range

where this dynamic is happening

is expanding.

ANDREW TANENTZAP:
Another major change

that we're seeing happening
around lakes

is that cattails are moving
northwards into the lakes

where they previously
didn't grow.

And where we compared
the effect of cattails

versus pines and oaks and maples

on the amount of methane
released from lake sediments...

..what we found was

that there was at least
400 times more methane produced

when we added the cattail litter

than any of the tree litter.

NARRATOR: Models show
that in the next 50 years,

cattails around lakes
will double

and since more cattails
means more methane,

methane production is predicted
to increase by 70%

across all northern lakes.

From the global climate
perspective, this is something

that we really need
to be worrying about

and thinking about how
to actually mitigate

and offset these processes.

NARRATOR: At Earth's poles,

snow and ice reflect
up to 85% of the sun's rays

away from the surface
and back into space,

helping to keep the planet
from becoming too hot.

Today,
that equilibrium is at risk

as one of the most important
cooling mechanisms,

the albedo effect or Earth's
reflectivity, is threatened.

Over the past few decades,

this natural mirror has begun
to break down

as fossil fuel emissions
raise temperatures,

melt snow and ice cover

and reduce the planet's albedo.

As the planet loses its ability
to reflect sunlight,

a dangerous warming
feedback loop is triggered.

The most alarming change
is happening in the far north

where the temperature rise
is causing the snow cover

and sea ice
to rapidly disappear.

Don Perovich is
a sea ice geophysicist

at Dartmouth College.

For the past 30 years,

he's been documenting
big changes in the Arctic.

DON PEROVICH: There's always
been this annual cycle.

The ice grows usually, say, for
nine or ten months of the year,

then melts
for a couple of months.

What's changing now
is the timing.

The melting is starting earlier,

the freezing is starting later.

We have much less coverage
every month of the year,

particularly at the end
of summer.

NARRATOR: Global warming
from human-caused emissions

of heat-trapping gases,

carbon dioxide, methane,
nitrous oxide and others,

is increasing the temperature
in the Arctic

two to three times faster
than the rest of the planet.

But that warming is then
amplified by the loss of albedo

as the reflective ice
and snow disappear.

DON PEROVICH: Say it's April

and we're flying
above the Arctic

and we look down
at the sea ice cover.

It's covered by snow,
it's bright and it's white.

Now, summer comes,
that snow melts.

You get more open ocean.

You're absorbing much more heat.

Instead of reflecting 85%,

you're absorbing 90%.

And so you're replacing one
of the best natural reflectors,

snow,

with one of the worst,
the open ocean.

NARRATOR: Now, instead
of reflecting the sunlight,

the ocean absorbs it,

heats up and melts more ice,

exposing more dark ocean

which absorbs more sunlight

in an amplifying cycle.

GEORGE WOODWELL:
As those darker waters warm,

they emit carbon dioxide
and water vapor,

warming things further.

So, there are several aspects

to this feedback
in the Arctic problem

which are truly frightening.

NARRATOR: Scientists have been
measuring Arctic sea ice

since long before satellites
began taking

reliable measurements
in the early 1970s.

By the end of that decade,
the climate models predicted

sea ice would begin
to disappear with the increase

of heat-trapping gases
in the atmosphere.

Marika Holland is
a climate modeler

from the National Center
for Atmosphere Research.

MARIKA HOLLAND:
So, our first climate models

were developed in the 1970s.

Those models,
even in their simplicity,

predicted that
with rising greenhouse gases

in the atmosphere,

we would see dramatic
sea ice loss in the Arctic

and the Arctic warming
would be amplified,

relative to the globe.

NARRATOR: And as measurement
techniques improved,

scientists were alarmed
to discover

just how much ice had been lost.

The volume has decreased by 75%

in only 40 years.

It's just a breath-taking
change in a very short time.

We call it the New Arctic now

because it's so different
from what it used to be.

The ice now is mainly consisting

of what we call first-year ice

which is just ice that's formed
in that one winter.

And most of it doesn't survive
through the summer.

It all melts.

NARRATOR: Studies suggest
that around a quarter

of global warming is caused
by the loss of this sea ice.

And if you factor in
the melting of snow cover

on the surrounding land,

together they account
for an estimated 40% loss

in the planet's reflectivity.

MARIKA HOLLAND: The snow cover
over land is very bright

and very reflective.

It reflects an enormous amount
of the sunlight

away from the surface, just
like the sea ice cover does.

And we are seeing reductions

in the aerial coverage of snow
over the land,

just like we're seeing
reductions

in the aerial coverage
of sea ice.

NARRATOR: With feedback loops
amplifying the warming,

the landscape of the Arctic
will change irrevocably.

MARIKA HOLLAND: So,
our climate model projections

suggest that we will lose
the Arctic sea ice cover

in the summer months altogether
by the end of this century.

If we continue
to increase greenhouse gases

in the atmosphere through
the burning of fossil fuels,

we ultimately will get
to a state

where we lose
the winter sea ice as well.

NARRATOR:
A sobering prediction,

considering that ice
has covered the Arctic Ocean

for more than two and a half
million years.

And the warming
happening in the Arctic

isn't staying in the Arctic.

The air there is mixing
into the global atmosphere

elsewhere on Earth

and raising global temperatures.

MARIKA HOLLAND: The Arctic
plays a very central role

in Earth's climate.

Even if you just lose
sea ice cover in the Arctic,

the tropics will feel
that enhanced warming.

NARRATOR: This means
amplification of problems

the climate crisis
is already causing -

crops suffering,

food prices going up...

..wet areas becoming wetter...

..dry areas becoming drier.

And as the climate warms, it
kicks in another feedback loop,

set in motion by the melting
of massive glacial ice sheets.

In the past 30 years,
the loss of ice

on the Greenland ice sheet
has increased six-fold,

leading to a rise in sea level.

As the ocean rises,

the higher, warmer water
melts more land ice,

raising sea levels further

and melting even more ice

in a vicious cycle.

In the South Pole,

the increased temperature
is thawing

the miles-thick
Antarctic ice sheets

that have been accumulating
on land

for over 40 million years.

MARIKA HOLLAND: Loss of ice
over the Antarctic continent

doesn't have as much
of an albedo feedback

because it's so thick,

but as that ice enters
the ocean,

it causes sea level to rise.

NARRATOR: If both Greenland

and Antarctica's glacial
ice shelves were to melt,

sea levels would potentially
rise by more than 100 feet.

This resulting destruction
to coastlines

would uproot millions of people
around the world.

It would also mean

the ice sheets would reach
a tipping point,

taking thousands of years
to recover.

So, if we lose an enormous
amount of ice from the land,

re-establishing that is
a very long timescale issue.

NARRATOR: And if we continue
with business as usual,

the warming of the Arctic
will cause the feedback loops

at both poles
to spin out of control.

MARIKA HOLLAND:
The models predict,

if we continue
on the path we're on,

that the Arctic will experience
very dramatic changes

and that those changes
will reverberate

throughout the system,

the human system,

the biological system,

the socio-economic system.

NARRATOR:
White, puffy cumulus,

dark nimbus storm clouds,

wispy, thin cirrus clouds.

Not just beautiful to look at,

clouds play an important role
in Earth's climate.

They're formed by water vapor,

a naturally occurring gas
created

when water evaporates
from lakes and oceans.

Water vapor is also
a heat-trapping gas.

It's part
of a dangerous feedback loop

that's heating the Earth
beyond its natural limits,

accounting for about 60%
of all global warming

caused by heat-trapping gases
in the atmosphere.

As fossil fuel emissions
raise temperatures,

the atmosphere absorbs
more water vapor

which then traps more heat,

warming the planet further

in an ever-amplifying loop.

In fact,
the water vapor feedback

amplifies global warming
from human activity

between two and three times.

For the past 30 years, Jennifer
Francis has been studying

how increased greenhouses gases
affect the atmosphere.

JENNIFER FRANCIS:
Water vapor is just water

in a gaseous form.

When you take a pot of water

and put it on your stove
and boil it,

you see steam which is still
in the liquid form,

but then it disappears

and it goes into the atmosphere
and it's completely invisible.

So, the same kind of thing
is happening

in the climate system

where as we warm the air
and we warm the oceans,

more evaporation is occurring
from the oceans

and putting more water vapor
in the atmosphere.

NARRATOR: While some of this
stays in the atmosphere

and traps heat in gaseous form,

some of it cools and condenses,

forming clouds which can both
heat and cool the planet.

We still don't have
good mechanisms,

as good as we would like,

for cloud feedbacks...

..because clouds are
very complicated.

NARRATOR: Clouds can lower
the temperature

because their white color
reflects sunlight

back into space,

cooling the Earth
like on a hot, sunny day

when clouds offer relief
from the heat.

Conversely, clouds
can trap heat below them,

heating Earth's surface

like when it's warmer
on a cloudy night

than on a clear one.

Scientists conclude that,
on balance,

clouds raise the temperature.

And as the climate warms,
the oceans are also heating up,

causing increased evaporation,

creating even more water vapor,

trapping more heat,

leading to more evaporation

and becoming
another amplifying loop.

It's this combination
of increased water vapor

and the warming of the oceans
that's driving hurricanes.

KERRY EMANUEL:
More than 30 years ago,

we predicted that
global warming would result

in more intense storms,

and we're beginning to see that,

even in places
like Florida and the Bahamas

which are adapted to hurricanes.

They're adapted up to a point

and when we begin to see
stronger storms like Dorian,

that adaptation
doesn't mean anything.

NARRATOR:
In addition to water vapor,

another atmospheric
feedback loop

is creating extreme weather,

this one involving
the jet stream.

JENNIFER FRANCIS: The jet
stream is this river of wind

high over our heads,
up where the jets fly,

that encircles
the Northern Hemisphere

and that jet stream
is responsible

for creating
pretty much all the weather

that we experience
in this part of the world.

NARRATOR: To illustrate,
imagine a layer of air

extending from the warm south
to the cold north.

Warm air expands,

so the layer over the south
rises up higher

than the air over the north.

Because of gravity, the warm
air higher up flows downhill,

just like water flows
down a mountain.

This downward movement creates
a south-to-north wind.

But because the Earth
is spinning,

this wind gets turned
to the east

and becomes
a west-to-east flow of wind.

That's the jet stream.

The greater
the temperature difference

between the north
and south air masses,

the faster and stronger
the jet stream winds blow.

Historically,
Arctic air has been much colder

than the air to the south,

keeping the jet stream
fairly straight

with relatively small
north-south meanders.

But with the Arctic warming

at two to three times the rate
as the rest of the globe,

that temperature differential
has decreased.

This weakens
the jet stream winds,

causing them to take larger
swings north and south...

..which, in turn,
impacts the weather.

JENNIFER FRANCIS:
This is the feedback loop.

We're warming the Arctic,

we're reducing the winds
of the jet stream,

we're seeing it take
these bigger north-south swings

which then transfers
even more heat

from the south to the north
into the Arctic

which makes it even warmer,

which weakens the winds more

and it sets up
this vicious cycle.

NARRATOR: Recent examples
are the multi-year drought

in the western US

and the increase in wildfires.

They're connected
to a larger north-south swing

in the jet stream.

We're now living in a world
where extreme weather events

like these are the norm,
not the exception.

Even if we could staunch
the emissions

of greenhouse gases today,

these weather patterns
may continue

for a long time to come.

JENNIFER FRANCIS:
So, the wet places

are going to tend to get wetter.

On the other hand,
places that are already dry,

they're also going to see
more evaporation

because of the air being warmer.

Where we are now, it's like
driving in a car in a dense fog

and you know there's a cliff
out there somewhere,

but you don't know where.

Do you want to be going
60 miles an hour

or should you be going
about ten miles an hour?

NARRATOR:
Today, we have a choice.

If we take our foot
off the accelerator,

we can reverse
the feedback loops

and begin to cool the planet.

If we don't deal with
this climate change issue...

..we're going to be
in deep trouble.

KERRY EMANUEL: The emission of
greenhouse gases is an example

of a market failure,

one business enterprise
passing on the real cost

of doing business to people who
aren't party to that business,

that is, most of the rest of us.

NARRATOR: George Woodwell
was an early pioneer,

warning about fossil fuel use

setting off warming feedback
loops five decades ago.

He's convinced the solution lies

with nature's own ability
to cool the planet.

GEORGE WOODWELL:
We can store carbon in life.

If we want to be optimistic,
we have to be very progressive

in our transition
away from fossil fuels

and into a new green world.

NARRATOR: With every country
contributing to the problem,

each now needs to be
part of the solution.

GEORGE WOODWELL: And that
requires managing the world

in such a way that we do not
exploit carbon compounds

and dump the waste
into the atmosphere.

NARRATOR:
In every sector of the economy,

we have the technology
and knowledge

to move
towards sources of energy

that do not produce
heat-trapping gases.

What we need is the will.

KERRY EMANUEL:
I'm encouraged by the fact

that other countries
have decarbonized

their electricity sector
in ten to twelve years,

so I know we can do it

and those countries that did it

grew their economies rapidly
while doing it.

But we have to put
the incentives in place.

(CHANTING)

The most important thing
citizens can do

is to educate themselves
on this issue

and vote for politicians
who take this problem seriously

and have good ideas
for how to solve it.

SUE NATALI: Communicating
with our policy-makers

that this is important to us,

that this is impacting
each one of us,

that this is important

for human health,
for human well-being,

is the most important action
that each one of us can take.

PHILIP DUFFY: To successfully
address climate change requires

an unprecedented level
of societal cooperation,

cooperation across nations,
cooperation within nations,

across multiple sectors.

NARRATOR:
Today, we have a choice.

We can continue
with business as usual

and let these warming feedback
loops spin out of control

or we can choose
another way of living

and implement policies that
support a sustainable future,

but we need leaders

who understand the urgency
of getting it done

and an energized public
to advocate for change.

(GRETA THUNBERG SPEAKING)

We, the people.

Thank you.

Most people I know, I encounter,

haven't even heard of feedback
loops or tipping points,

chain reactions and so on.

But they are so crucial

to understanding
how the world works.

We have... we have
such a lack of respect

for nature
and for the environment

that we just think that things
will work out in the end.

We cannot solve
the climate emergency

without taking these feedback
loops into account

and without really
understanding them,

so that is a crucial step.