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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.