All language subtitles for NOVA.S49E01.Arctic.Sinkholes.1080p.WEB.h264-BAE_track3_[eng]

♪ ♪

NARRATOR:
What happens when a frozen world
locked away for millennia

starts to thaw?

In 2014, a helicopter crew
flying over Siberia

discovers something mysterious:

a crater more than 80 feet wide

and deeper than a 15-story
building.

Sinkholes are nothing new,

but this is no ordinary
sinkhole.

SUSAN NATALI:
The ground has exploded.

There's no way...
This is not real.

NARRATOR:
More Siberian craters
have since been discovered.

There's even evidence
they may be appearing in Alaska.

TAYLOR SULLIVAN:
The lake bottom went from being

flat, flat, flat,
and then it just dropped out.

NARRATOR:
And they show no sign
of stopping.

Now, scientists from around
the globe race to understand

a hidden world:

permafrost,
a layer of frozen earth

spanning a quarter of the
Northern Hemisphere's land mass.

This ancient freezer
is beginning to thaw,

revealing its deepest secrets...

Pretty exciting, this is a
mammoth bone right here.

NARRATOR:
releasing over half a billion
tons of carbon every year...

JANELLE SHARP:
It was just insane,
like, the water

is boiling around you.

NARRATOR:
and threatening local
communities.

LARS NELSON:
Houses need to be torn down.

We're in the middle
of a housing crisis.

♪ ♪

NARRATOR:
Are the craters warning shots
for our climate future?

KATEY WALTER ANTHONY:
That is not included
in climate models.

That's a scary wildcard
in the climate change story.

NARRATOR:
What new dangers lurk beneath

this vast frozen landscape?

And could they warm our planet
even further?

"Arctic Sinkholes."

Right now, on "NOVA."

♪ ♪

(wildlife chirping, chittering)

NARRATOR:
The Yamal peninsula, Siberia.

47,000 square miles
of freezing tundra.

♪ ♪

Located in Northern Russia,

the Yamal lies well above
the Arctic Circle.

It's home to around 10,000
Indigenous Nenet people,

most living as nomadic
reindeer herders.

♪ ♪

In their language,
Yamal means "end of the land."

It's now beginning
to look like it.

♪ ♪

Giant craters were spotted
in the North of Russia.

They popped up out of nowhere
in the Yamal peninsula.

NATALI:
When I first heard about
the crater, I didn't believe it.

I actually thought it was
a made-up story.

♪ ♪

MARINA LEIBMAN:
Believe me, I remember this
date,

and I will remember it forever,

because it was
absolutely exciting,

something I have never
seen before.

NARRATOR:
The mysterious crater
is 150 feet deep.

Filled up with rainwater,

its volume is greater than
ten Olympic swimming pools.

The striking images go viral
worldwide

because no one can answer,
what caused it?

♪ ♪

Vasily Bogoyavlensky
is an expert

on the geology of the Yamal.

With other scientists,
he choppers out to the scene.

♪ ♪

BOGOYAVLENSKY:
When we just came to
this crater, of course,

we didn't know for sure
what was there.

We never saw something
like that, never.

♪ ♪

NARRATOR:
This isn't the first massive pit
to open up.

(people crying out)

♪ ♪

Across the world,
gaping sinkholes

have appeared due to water

or erosion weakening the ground
beneath,

swallowing cars whole

and wreaking havoc in towns
and cities.

But while the Yamal crater
looks at first

like an ordinary sinkhole,

there's something unusual
visible around the edges.

(Bogoyavlensky speaking Russian)

♪ ♪

NARRATOR:
Most sinkholes have a rim
that is flat, not raised.

And while sinkholes
collapse inwards,

the team discovers debris
spread far outside the crater.

Pieces of rocks and ice
are flying,

sometimes in quite
long distance,

from 200 meters to 500 meters.

And in one case,
it was distance to 900 meters.

NARRATOR:
Debris like this

can be thrown out by the impact
of an asteroid.

But there are no other signs
of a massive object

striking Earth.

For the scientists,
that leaves only one

reasonable explanation.

A gigantic natural explosion.

NATALI:
I don't know if there are many

Earth system processes
that have never occurred...

I mean, in my lifetime,

or at least to scientific
understanding...

that have never occurred
and that we're starting to see

as a new process.

NARRATOR:
So what could have provided the
power for such a massive blast?

There is no sign of lava
or volcanic rock,

so this clearly isn't a volcano.

But exploring inside the crater,

sampling the air and water
at the bottom,

the scientists do discover
an intriguing clue:

unusually high levels
of a single gas, methane.

♪ ♪

Used for cooking and heating,

methane is a flammable gas
made from carbon and hydrogen.

(exploding)

When combined with air,
it ignites easily.

♪ ♪

BOGOYAVLENSKY:
So this is huge bomb.

Methane bomb.

NARRATOR:
But before scientists
can determine

where the methane came from...

...more giant craters
are discovered.

Investigating, scientists find
new evidence of methane.

Since 2014,
at least eight confirmed craters

have been found on or close to
the Yamal.

But the growing number
of craters

isn't the scientists'
only concern.

They notice a climate
connection.

(birds twittering)

2014,
when the first crater appears,

followed one of the hottest
years on record in Russia.

And all the craters are
discovered during a period

of uncharacteristically
warm weather in Siberia.

Since the late 19th century,
the average global temperature

has risen around two degrees
Fahrenheit.

But the Arctic
is warming faster.

It's currently heating up
around twice as fast

as the rest of the planet.

♪ ♪

The scientists begin to ask:

could the explosive craters
be connected to climate change?

If so, what might they be
telling us

about Earth's climate future?

♪ ♪

While scientists on the Yamal
study the crater,

elsewhere in the Arctic, another
team is about to discover

new pieces of the puzzle.

This time, in Alaska.

♪ ♪

Kotzebue,
near Alaska's northwest coast.

In 2017, a local pilot reports
a lake that's behaving oddly.

Now, a team of scientists

that had been investigating
returns to the site

to continue its work.

PHIL HANKE:
So we just left Kotzebue,

and then we crossed
the Kotzebue Sound,

and into the mouth
of the Noatak,

which was this, like,
beautiful, sweeping landscape.

SHARP:
Look, there's the lake
right there!

Man, that's exciting!

♪ ♪

NARRATOR:
Far from the nearest town
lies Esieh Lake.

Field technician Phil Hanke
proceeds cautiously,

hoping to avoid surprises.

Hey, bear!

SHARP:
Hey, bear!

HANKE:
Hey, bear!

Bear scat.

Well, there's, uh,

definitely bears around here,

so we're going to have to
take that into account

when setting up camp.

♪ ♪

NARRATOR:
Esieh Lake is located
on the lands of

the Indigenous Inupiat people.

The state is home to over
13,000 Inupiaq people,

whose traditional lands
stretch across Northern Alaska.

One of the scientists
on the team has special ties

to this community.

My name is Janelle Sharp,
my Inupiaq name is Anausuk.

My mom is originally
from Kotzebue.

My family is from this region.

And so this project is really

special to me, because it's
kind of, like,

me coming back to my roots.

♪ ♪

NARRATOR:
In 2017, Sharp and other
scientists

asked the local community
to help them identify

unusual features
in the wilderness.

A pilot named Eric Sieh
told them that while flying over

the area,
he'd spotted something unusual.

♪ ♪

SHARP:
If you fly low enough,
even from the air,

you can see the bubbling.

♪ ♪

HANKE:
It's just mysterious.

It looks like a Jacuzzi.

And so you, you get up to it,
and you can hear this...

(imitates bubbling)

Like, the water is boiling
around you.

(water bubbling loudly)

♪ ♪

NARRATOR:
On their first visit,
the team wanted to investigate,

what's causing the bubbles?

SHARP:
We took gas samples,

and then those were sent to
the lab for analysis,

and they found that it is
a super-high amount of methane.

NARRATOR:
Methane leaks, known as seeps,

have been found elsewhere
in the Arctic.

But they're usually
much smaller.

The team's measurements reveal
that Esieh Lake is belching out

over ten tons of methane
every day.

SULLIVAN:
This is the highest flux

methane seep that humans
have discovered in the Arctic.

The amount of methane you see
is staggering.

♪ ♪

NARRATOR:
From the shore,
it's difficult to see

where the methane
is coming from.

So the team decides
to get closer to the source.

SULLIVAN:
Hypothermia is obviously
the main danger.

Second is me getting air.

I'm very curious about
what's down there.

♪ ♪

NARRATOR:
Sullivan finds that the lake is
shallow... just a few feet deep.

But then,
he follows the lake floor

towards the source
of the bubbles.

SULLIVAN:
I was kicking really hard

to stay down along the bottom,

and I was moving my hands
along it.

And it went from this mushy
lake bottom

that was flat, flat, flat,

and then it just dropped out.

♪ ♪

SULLIVAN:
That gets deep so quickly.

HANKE: Yeah.
It's like you're on
the bottom,

you're on the bottom,
bottom's gone.

NARRATOR:
Sullivan finds the
methane bubbles are streaming up

from the hole in the lake floor.

SULLIVAN:
The bubbling,

it, it sounded like seeping gas,

as if it was even from
a propane tank.

♪ ♪

HANKE:
How'd it go?

SULLIVAN:
Still going down!
SHARP: Wow.

(breathing heavily)

NARRATOR:
With the lake bottom
too dark to see,

the team deploys a sonar scan.

Most of this bed is around
three feet deep.

But beneath the streams
of bubbles,

the ground abruptly falls away,

at its deepest reaching 50 feet.

Why does a lake floor

otherwise flat and shallow
contain such a massive hole?

(rotor blades whirring)

On the Yamal, scientists believe
a methane leak

blew out a huge crater.

Esieh Lake is another sign
within the Arctic

that beneath the surface,
methane is stirring.

So could more craters...

And more methane...
Be on the way?

♪ ♪

As well as methane,
there's one more clue that links

Esieh Lake
and the Yamal craters.

(birds twittering)

Both are located on the same
type of frozen terrain:

permafrost.

♪ ♪

Most permafrost is found
in the land masses

of high northern latitudes,

including Russia, Canada,
and most of Alaska,

Covering an area almost as large
as the U.S. and Canada combined.

Permafrost can stretch almost
a mile beneath Earth's surface.

It's defined as any ground
whose temperature remains at

or below 32 degrees Fahrenheit

for two or more
consecutive years.

But it can remain frozen
for millennia.

♪ ♪

Recently, rising Arctic
temperatures have meant that

in some regions, the permafrost
has started to thaw.

(birds twittering)

Just how fast

and the danger this may pose
to our climate

is revealed 450 miles
from Esieh Lake.

Near the town of Fox,
in Interior Alaska,

something strange is happening
in the woods.

(birds twittering,
branches rustling)

♪ ♪

TOM DOUGLAS:
This is what people refer to

as this drunken forest.

You can see a bunch of these
have kind of started to go.

They're just having a hard time
getting enough rooting in

to grow straight.

NARRATOR:
This forest sits on top of
permafrost.

Scientist Tom Douglas has been
tracking some

surprising changes taking place

as the permafrost starts
to thaw.

DOUGLAS:
I mean, look at those
huge birch trees.

They're literally just

riding down those slopes
as it's all degrading.

♪ ♪

I mean, this goes a good
20 or so meters below us.

This is a giant hole.

You can hear water in there.
(water rushing)

This whole landscape
is just very slowly

sliding downhill with gravity.

♪ ♪

This is a very dramatic

and very rapid change
in the landscape here

that, again, we're seeing
in a matter of years.

Not decades, not 20 years,
not by 2100.

Since 2018.

It's pretty dramatic.

♪ ♪

NARRATOR:
This rapid thaw is also
affecting human settlements.

Like Utqiagvik,
the most northern city

in the United States.

♪ ♪

This entire community sits on
top of the Alaskan permafrost.

Locals call it
"the top of the world."

♪ ♪

GORDON BROWER:
If you point that way,

that's Greenland over there.

Canada is over here.

And that way is, guess what.

(laughing):
Russia.

NARRATOR:
Gordon Brower

is a Native Alaskan Inupiaq
whaling captain.

His people have lived in this
region for thousands of years.

BROWER:
Communities like these,
they're special.

A lot of the cultures
in the world

are assimilated,
and we're assimilated here,

but we brought our culture
and our ways

to the future with us.

And you can come here and still
see the same celebration

that took place
10,000 years ago.

♪ ♪

NARRATOR:
For five decades, Brower has
been hunting in these waters,

part of an ancient Inupiaq
tradition of living off the land

and the sea.

We don't have Walmart or we
don't have McDonald's up here.

We have other small restaurants

and other things to do
like that.

But the majority of
food resources

are still hunted today:
seals, whales, belugas,

ducks, geese,

caribou, wolves...

All of those
are still traded and used.

NARRATOR:
With little fresh food available

in winter, generations of
Native Alaskans have depended on

cellars carved out
of the permafrost.

BROWER:
Well, we're in an ice cellar.

My folks used this ice cellar
for years and years.

This is where I put a whale

and store it in trust
for the community.

NARRATOR:
But thawing permafrost means
this natural deep freeze

isn't as cold as it used to be.

As Brower discovered.

BROWER:
I had checked on the meat
and told my brothers,

you know, "We got to pull that
meat out.

It's draining,
and we don't want that."

I've resorted to pulling
a whole whale out of there

and putting it into
walk-in freezers.

♪ ♪

NARRATOR:
Thawing ice cellars aren't the
only threat rising temperatures

pose to this community.

Recently, sea ice that used to
protect the shore

from storms has begun to melt.

BROWER:
Storm surge is pretty dramatic.

And it's going to

wreak havoc on your coastline
here.

And the thing about is,
when it's reaching the edge,

a lot of the banks
are permafrost-rich,

and it undercuts them.

NARRATOR:
Exposed by the storms,

permafrost is thawing
and crumbling away.

Now communities like Utqiagvik

are trying to protect
their homes.

BROWER:
These are all

our local efforts to stop
the storm surge.

This is our way of trying to
save the town.

NARRATOR:
With a retreating coastline

and warming ice cellars,

local communities are hit twice
by thawing permafrost.

But the big thaw
is an Arctic-wide problem.

NATALI:
Through the next decades
and century,

we expect anywhere,
across the Arctic,

between 30% and 70%
of near-surface permafrost

will be lost.

That range partly has to do with
just some uncertainty

in the science,
but largely has to do with

how much warming will happen
in the future.

NARRATOR:
Arctic communities are facing
the immediate effects now.

But scientists are concerned
this loss has implications

for the entire planet.

So why is permafrost thaw
so dangerous?

And what is the link to methane?

(birds twittering)

Back near Fox
in Interior Alaska,

Tom Douglas is about to do
something only possible

in a few places on Earth...

Walk deep down into
the permafrost itself.

The Fox permafrost tunnel
reveals there's more

to permafrost than frozen earth.

DOUGLAS:
That's a horn.

That's from the longhorn
steppe bison.

And they are extinct now,

but back 18,000
to 40,000 years ago,

you know, there were
steppe bison here.

Pretty exciting,

this is a mammoth bone
right here.

You can just see kind of the

piece of it sticking out
right there.

It's pretty big.

NARRATOR:
The tunnel reveals
that permafrost contains

vast quantities
of organic matter.

DOUGLAS:
So these are,

these are sedges,
kind of like grass.

And you can see that they,
they're green.

They still have their
chlorophyll in 'em.

They're also upside down.

This block fell into
a water feature that then froze,

probably 20,000 or so years ago.

♪ ♪

NARRATOR:
This ancient organic matter,

like all life on our planet,
contains carbon.

(birds twittering)

And is part of a vital
Earth system called

the carbon cycle.

♪ ♪

As they grow,
plants absorb carbon dioxide.

When they die, they, or the
animals that have eaten them,

decompose,

releasing some of this carbon
back into the atmosphere.

But in the freezing Arctic,

decomposition happens slowly.

So over millennia,

a huge amount of organic matter
became permafrost

before it could decompose,

its carbon frozen in time.

DOUGLAS:
In the late '90s into the 2000s,

people start to look at the
stocks of carbon in permafrost.

And it's, it's a lot, it's about
1,400 billion metric tons.

It's almost twice as much carbon

as is currently in Earth's
atmosphere.

When we walked in,
we noted that smell, right?

You're smelling ancient bacteria
and carbon being oxidized.

It's almost like a, well,
I've heard anything from, like,

a French cheese, to barnyard,

but it's kind of that organic,
almost a late fall,

wet leaf kind of organic smell.

You are smelling permafrost
carbon being oxidized.

And so the big question

is, that carbon that we smell,
that's all over

this tunnel walls,

what's its ultimate fate?

And there's a lot of people
working on that.

NARRATOR:
In other words,
how much of this carbon

will end up in the atmosphere?

And most importantly, how fast?

♪ ♪

Falmouth, Massachusetts.

3,000 miles from the ice tunnel.

Arctic ecologist Susan Natali
investigates

samples of permafrost

to find out what happens
when it thaws.

NATALI:
So these are permafrost cores
that were collected

from different locations
across Alaska.

Some of these are really dark,
like particularly this one.

And that dark color

means that that has
a lot of carbon in it.

♪ ♪

NARRATOR:
As permafrost warms,
its carbon thaws.

And the carbon cycle starts up
once again.

So that carbon then is available
for microbes to break down.

And they use it for energy
and they decompose it.

And in that process,
they're releasing

carbon dioxide or methane.

♪ ♪

NARRATOR:
Carbon dioxide and methane
are both greenhouse gases.

As Earth's surface absorbs
energy from the sun,

it radiates some of it
back out as heat.

In the atmosphere, greenhouse
gases absorb this heat,

radiating part of its energy
back at Earth

and heating up our planet.

NATALI:
Greenhouse gases are a concern
because they trap heat.

They're helpful to us because

they, they make this
habitable planet,

but because there's too much
in the atmosphere,

they're now making this
an unhabitable planet,

or less habitable planet.

♪ ♪

NARRATOR:
It's estimated that
in the mid-18th century,

there were over 2,000 gigatons
of naturally occurring

carbon-based greenhouse gases
in the atmosphere.

With industrialization,

human-made greenhouse
gas emissions

began to add to this amount.

By 2019, it's estimated
the total had risen

to over 3,000 gigatons.

Over the last century
and a half,

Earth's average temperature
increased around

two degrees Fahrenheit.

♪ ♪

Scientists agree human emissions
caused this warming.

But recently,
they've become concerned

greenhouse gases
being released by permafrost

might be driving
temperatures higher, too.

As the name suggests,

permafrost
is permanently frozen ground.

So we thought,

"Okay, this carbon is

very stable, so
nothing is going to happen."

But as permafrost
starts to thaw,

this carbon becomes vulnerable.

NARRATOR:
Since the mid-'70s,

carbon dioxide emissions

from the
North Alaskan wilderness

have spiked by more than 70%.

But while we know a lot
about carbon dioxide,

the impact of
another greenhouse gas

coming out of the permafrost
is less widely known...

the very one escaping
from the Yamal and Esieh Lake,

methane.

Methane is really important,

because it's much more potent

in terms of
its ability to trap heat.

So it's about 30 times more
powerful than carbon dioxide.

♪ ♪

NARRATOR:
Luckily, while carbon dioxide

lasts centuries or longer
in our atmosphere,

methane only lasts
around 12 years.

But as a far more potent
greenhouse gas,

any large-scale increases
in methane emissions

have climate scientists
seriously concerned.

♪ ♪

For now, more than half of
methane emissions

come from human sources like
fossil fuels and agriculture,

sources well understood
by climate experts.

But scientists
are increasingly worried

about methane emissions
from permafrost.

So far, they don't know

how much methane
the permafrost is releasing.

And that's a big problem.

In order to
control our temperature,

we have a certain
amount of carbon

that humans can release...
That's our carbon budget.

NARRATOR:
In 2015,

the international
Paris Agreement

set a target
for limiting global warming.

Its goal was
to keep the temperature rise

to well below two, preferably
to 1.5 degrees Celsius.

To stand a good chance

of remaining below
the 1.5-degree mark,

one estimate states that humans
could release a maximum of

around 460 gigatons more
carbon dioxide.

But recent climate calculations
are based on computer models

with incomplete information.

LEE:
Unfortunately,

a lot of these
Earth system models

that contribute to such goals

do not take into account CO2
and methane emissions

from permafrost.

NARRATOR:
The most recent carbon budgets

have started to
include permafrost carbon.

But some scientists believe
they still underestimate

the amount of carbon
the warming Arctic will release,

making temperature goals
harder to meet

and putting more pressure
on societies

to dramatically cut
their emissions to compensate.

NATALI:
So we think we have

a certain amount
of greenhouse gases

that humans can release,

but our target
is wrong right now,

because we're not accounting for

potential permafrost emissions

of methane and carbon dioxide.

NARRATOR:
Understanding the dynamics
of thawing permafrost

is now critical to
predicting our climate future.

So how much methane is
permafrost emitting each year?

And is this annual amount
going to increase?

(dogs yapping)

HANKE:
Good dogs!

Straight ahead,
on by, on by, on by.

NARRATOR:
Fairbanks, Interior Alaska.

Ecologist Katey Walter Anthony

is heading out
onto the frozen terrain.

HANKE:
Haw! Haw!

Come on, Biggy, come on.

(dogs whining)

NARRATOR:
Walter Anthony was

among the first
to study Esieh Lake.

She's found concerning evidence

it's not the only lake
in the permafrost region

that's releasing methane.

♪ ♪

WALTER ANTHONY:
So when you spear the spot,

if I hear gas coming out,

I'm going to try to ignite it.

And if there's fire, we both
need to get out of the way.

Okay.

Ready?
Yep.

Whoa...
(flames roaring)

That got me.

Oh, shoot.

Am I on fire?

No... I was wondering.

(both chuckle)

What's smoking?

(laughing)
You okay?

(laughing):
Yeah, I'm fine.
(laughing)

That was a good one.
That was a good one.

All right.

NARRATOR:
The methane comes from

organic matter in permafrost
thawing and decomposing

at the bottom of the lake,

then rising in
methane bubbles to the surface.

Across the Arctic,
permafrost thaw

is generating
vast numbers of new lakes.

As the soil warms,

ice beneath the surface melts,

causing the ground to
slump and fill with water.

And once a lake is formed,
you can't stop it,

because that water has heat,

and it causes the ground
to thaw so fast.

NARRATOR:
The lakes then start
releasing methane.

WALTER ANTHONY:
As the methane escapes,

it causes more
permafrost to thaw,

and more methane to be
generated,

which is more warming,
and you get what's called

a positive feedback cycle.

NARRATOR:
Positive feedback cycles

from permafrost regions

are another scenario not
sufficiently accounted for

in current climate models.

LEE:
As permafrost thaws,

greenhouse gases
like CO2 and methane

will be released back
to the atmosphere much faster.

Warming is causing more warming.

NARRATOR:
Due to positive feedback,
permafrost emissions

could increase
the rate of warming,

compounding the need for humans
to reduce their emissions

if climate targets
are to be met.

But permafrost carbon
isn't the only potential driver

of a positive feedback cycle.

Permafrost is actually not
the largest carbon reserve

on Earth.

There's much
larger carbon reserve

in Earth's crust as
fossil carbon.

But we often don't
talk about this carbon.

This is because this carbon is
considered very stable.

NARRATOR:
But some scientists

now wonder if
this mega source of carbon

is as stable as they thought.

Disturbing evidence

comes from the bubbles
in Esieh Lake.

Methane released
by thawing permafrost

has a particular
chemical fingerprint.

When the scientists
at Esieh Lake

studied the methane
in the bubbles,

they discovered it originated
deeper inside Earth.

Much deeper.

♪ ♪

Miles beneath the permafrost,
deep in Earth's crust,

lie huge fossil
methane reservoirs.

While methane from permafrost

comes from organic matter
thousands of years old,

fossil methane
comes from organisms

that decomposed
millions of years ago.

But if it's miles
beneath the surface,

how is this methane
getting through Earth's crust?

And why here?

Above ground,

the landscape itself
gives scientists a clue.

SULLIVAN:
Looking up at the peaks
around here,

and studying the local geology,

we know that this is

a highly fractured and
faulted region.

NARRATOR:
As of 2021,
Alaska is the most

seismically active state
in the U.S.

In the territory
close to Esieh Lake,

scientists
have discovered a network

of geological fault lines.

Although not on
a tectonic plate boundary,

movements of Earth's crust
have caused it to crack here.

The closest fault line
discovered so far

is fewer than five miles
from the lake.

Fault lines make cracks
in Earth's crust

through which fossil methane
can rise to the surface.

Though it hasn't been confirmed,

the scientists suspect
a fault line lies near,

or directly beneath, Esieh Lake.

But if so, there's a mystery.

Seismic evidence
from the area suggests

Esieh Lake sits above 500 feet
of still-frozen permafrost.

This should form
a rock-solid frozen barrier

trapping the fossil methane
inside Earth.

So how are these
deep stocks of greenhouse gas

breaking through to the surface?

So far, the team's sonar scan

has revealed a 50-foot hole
in the lake floor.

But what if
they could look deeper,

into the permafrost itself?

Geophysicist Nick Hasson

joins the team,
with technology used

by the military.

75 just after the shrub.

HASSON:
I'm essentially scanning
the permafrost

using a geophysical method
called Very Low Frequency.

NARRATOR:
Very Low Frequency, or VLF,

measures a special kind of
electromagnetic wave

as it moves through Earth.

These waves are sent out
globally by the Navy

to communicate with submarines.

But as those waves
pass through the Earth below,

Hasson's equipment
can pick them up.

By measuring
the speed the wave travels,

Hasson can tell whether
the ground deep beneath him

is frozen or not.

When it moves
through the ground,

if there's permafrost or ice,

these waves
are coming up against

a lot of resistance.

But if there's
no permafrost or ice,

it quickly moves through.

NARRATOR:
If they're strong enough,

the electromagnetic VLF waves

should enable Hasson to see
whatever lies beneath the lake.

And so we can scan the Earth
similar to how a doctor

scans you with a MRI.

NARRATOR:
Esieh Lake is the biggest

on-land methane seep
yet found in the Arctic,

but no one has used VLF
to look beneath it.

Until now.

HASSON:
Wow.

Fantastic signals.

Yeah, so I'm starting
to notice a change.

Well, we're
over the largest seep,

and there's some sort of
large anomaly

happening right here
where I'm located.

And the VLF is picking it up.

It's very exciting.

The signals are
just outstanding.

♪ ♪

NARRATOR:
Back at camp,

Hasson takes the first ever
high-resolution glimpse

beneath Esieh Lake.

This slice through 500 feet
of ground below the lake

reveals an anomaly.

So the dark blue
is the permafrost region.

So anything that's
light blue to red is thawed.

And so this shouldn't be here.

There should be permafrost
covering this entire area.

But for some reason,

what you can see here
is a thaw chimney

going from somewhere
below 150 meters

to the surface,

where we see the rising bubbles.

And so this is really unique.

NARRATOR:
So far, the scientists
have only seen

50 feet beneath the lake.

Now, Hasson's VLF image
lets them look ten times deeper.

Below the lake stretches
a deep layer of permafrost.

But the scientists now know

this hasn't just thawed
at the surface.

Instead, a chimney of material
has thawed

right through
the frozen permafrost:

a warmer,
semi-permeable passageway

through which fossil methane
rises to the surface.

So, thawing permafrost
means not one,

but two sources of methane
for our atmosphere.

As it warms,

permafrost
releases its own methane gas.

And as thaw chimneys
form within it,

they provide an escape route
for fossil methane

that has been safely trapped
for millions of years.

Scientists estimate there are
around 1.3 trillion tons

of methane
stored beneath the Arctic.

That's nearly 250 times
as much methane

as there is in
Earth's atmosphere today.

So is Esieh Lake's
thaw chimney unique?

Or is fossil methane
escaping elsewhere?

While the leak in Esieh Lake
is unusually large,

smaller seeps of fossil methane

are being discovered
across the Arctic.

In Alaska alone,
over 70 sites have been found.

♪ ♪

There's no current sign
the entire reserve

of fossil methane
is moving toward the surface.

But the appearance
of even small amounts

of this ancient greenhouse gas
has some scientists concerned.

WALTER ANTHONY:
If permafrost thawed,

then that's a scary wildcard
in the climate change story,

because we think there's
a huge amount

of methane and natural gas

trapped inside permafrost
and under permafrost.

So if permafrost
becomes like Swiss cheese,

with lots of holes in it,

then you can have chimneys
where that gas is erupting out.

And that is not included
in climate models.

♪ ♪

NARRATOR:
If only a tiny fraction

of the fossil reservoirs
were to reach the atmosphere,

it could intensify warming,

putting even more pressure on
human emissions targets.

How fast that's going to happen

and just how much methane
will come out, we don't know.

NARRATOR:
Scientists don't
currently understand

how fast such a cycle
might occur,

or what it would look like.

But there's one place on Earth

that gives a chilling example

of how a human-made permafrost
feedback cycle actually works.

Northeast Siberia is home to
the Chersky Mountains.

In the 1960s,
in a place called Batagaika,

a stretch of forest
was cleared to make a road.

Stripped of its tree cover,

the permafrost was exposed
to the warming sun.

As it thawed, the ground sank,

pulling down trees at its edge
and exposing more permafrost:

a positive feedback cycle.

♪ ♪

Today,
the strip of cleared forest

is a depression
nearly 300 feet deep

and over half a mile wide.

And it's growing.

Scientists call it a megaslump.

LEIBMAN:
Batagaika,

it is very big,

but this, the size is because of
the initial human impact.

And this one is already
more than one kilometer,

and growing every summer.

NARRATOR:
Batagaika reveals
how a small human impact

can start a devastating
feedback cycle in permafrost.

(birds chirping)

Scientists are
now trying to discover

what a feedback cycle

could mean for
the entire permafrost region

and whether it could
reach a point where it becomes

irreversible.

Such a phenomenon
is called a tipping point.

SULLIVAN:
A tipping point is

the proverbial straw
that broke the camel's back.

You can get away with
adding straw for so long,

and then you can't.

And the tipping point
is the point of no return.

♪ ♪

NARRATOR:
It's a controversial idea
among climate scientists.

But the prospect
of a tipping point

has been raised for a number of
global climate systems,

including Arctic sea ice

and deforestation in the Amazon.

So far, there's
no conclusive evidence

that a tipping point
is near for permafrost.

However, some scientists
believe aspects of the thaw

are now irreversible.

(ground squelching)

Vladimir Romanovsky
has spent decades studying

the changing permafrost.

Near Utqiagvik
in Northern Alaska,

he investigates

what happens as large wedges
of ice in the ground

start to melt.

ROMANOVSKY:
Before,

it was more or less flat area,

but then ice melts

and surface subsides.

NARRATOR:
Romanovsky believes

lakes formed
by melting permafrost ice

have passed
a point of no return.

ROMANOVSKY:
It took tens of thousands
of years

to put this ice into the ground.

Now, it's, it's melting.

To put all this ice
into the ground back,

you will need several
tens of thousands of years.

So that's, for humans,
definitely irreversible process.

It is tipping point.

NARRATOR:
While melting ice forms lakes
in the wilderness,

just a few miles away, it's
causing very different problems

for the local community.

In the roads outside Utqiagvik,

the effects of
rising Arctic temperatures

are easy to see.

NELSON:
Just from observation,
growing up here,

coming out here
since I was a kid,

the roads were a lot higher
than they are now.

It is literally sinking.

His bumper might get wet.

NARRATOR:
Native Alaskan Inupiaq
Lars Nelson

is an infrastructure consultant.

He knows firsthand

what permafrost thaw
is doing to his community.

NELSON:
This road is for
subsistence use;

we come out here and
stage our hunts.

It's a big part of our history,
and it's important that

we're able to access it
in case of an emergency.

NARRATOR:
And it's not just the roads
that are sinking.

In downtown Utqiagvik,

Nelson meets
Inupiaq Anthony Edwardsen.

These ones are subsiding, too.

Yeah.

NARRATOR:
He's an expert on
the Inupiaq community

with four decades' experience
in the construction industry.

Yeah, look at...
This one is really messed up.

Look at how it's just...

EDWARDSEN:
That's where the houses
are sinking.

NARRATOR:
Local houses
are built on wooden pilings.

If they were
built on the ground,

the heat used to warm the homes

would thaw the permafrost below.

But now the permafrost
is thawing by itself,

and the pilings
are starting to sink.

EDWARDSEN:
When the piling is
a very small base,

it doesn't hold its structure.

The communities,

they need the house leveling,

move houses,
houses need to be torn down.

We're in the middle of
a housing crisis.

NARRATOR:
Nelson believes

strategic building
is the answer.

We're on to it right now,

and we're refining it right now.

We can build nice,
good, healthy homes.

We just got to pay
attention to our foundation,

pay attention to the tundra
we're building on more closely.

Because it's such
an awesome spot, you know?

It's the top of the world.

♪ ♪

NARRATOR:
But as the permafrost
continues to thaw,

others in Alaska are looking at
more drastic solutions.

GRIFFIN HAGLE:
So this is our portable,
adjustable,

sled-base home.

It is on a giant steel sled,

as opposed to the pilings.

NARRATOR:
C.E.O. of the regional housing
authority Griffin Hagle

has a more radical plan
for sinking homes.

HAGLE:
What we would do if we
needed to, to move this,

we would be hooking up
our tow chains

to these two attachment points.

We've got one on this side

and one on that corner
of the building over there.

Hook that up to a piece of
heavy equipment, Caterpillar,

and then drop it off the pads

and basically tow it
across the snow

in the wintertime.

♪ ♪

NARRATOR:
As temperatures rise,

Hagle is searching for ways

to protect some of the most
isolated communities

in the United States.

HAGLE:
This is the largest

municipality in the world,
I think, by land area.

We provide affordable housing

in eight villages across
an area the size of Minnesota,

only without any roads.

NARRATOR:
No Alaskan homes
have been sledded away,

yet.

But Arctic warming has forced
some towns to relocate.

And Hagle thinks houses
will soon be on the move.

And there are several,
you know, communities,

especially in rural Alaska,
Native communities,

that are increasingly
at risk of relocation

due to global warming.

And so this
gives us an advantage

in having the option,
the adaptability,

to move that, that structure
if it becomes necessary.

Native people,
the Indigenous communities

that have called this place home
for thousands of years,

have come up with
all sorts of innovations

to make life work here.

So we draw a lot of inspiration
from that,

and we see that as
kind of the continuation

of a long, long tradition
of innovation.

♪ ♪

NARRATOR:
As inhabitants across the Arctic

adapt to their changing world,

scientists strive
to build a better picture

of our climate future.

The methane craters are
just one sign of

a region undergoing
unprecedented changes...

...placing communities
with deep ties to this land

at risk.

BROWER:
We've been whaling here

well over 4,000 years.

(birds cawing)

We've adapted
time and time again.

Today, we might not be able
to do it by ourselves.

NARRATOR:
But the big thaw is
not just a regional problem.

What's happening in the Arctic
could really affect

everyone on Earth.

NARRATOR:
Arctic greenhouse gases

will intensify
future global warming.

How quickly
is difficult to predict.

And positive feedback cycles

could accelerate
beyond human control,

making our choices today
even more urgent.

LEE:
Because it's very difficult
to take control

over the natural systems,

it's even more important
for us to lower our emissions.

NATALI:
These craters are

a really important
and concerning indicator

that things are changing,
and the Arctic is melting,

and the Arctic is thawing.

And the future of the Arctic

is a very different place
than it was

several decades ago.

♪ ♪

♪ ♪

ANNOUNCER:
Episodes of "NOVA" are available
with Passport.

This program is also available
on Amazon Prime Video.

♪ ♪

♪ ♪