Nova (1974–…): Season 49, Episode 5 - Arctic Sinkholes - full transcript

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.

The ground has exploded.

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

More Siberian
craters have since been discovered.



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

The lake bottom went from being

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

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.

Releasing over half
a billion tons of carbon every year...

It was
just insane, like, the water

is boiling around you.



And
threatening local communities.

Houses need to be torn down.

We're in the middle
of a housing crisis.

Are the craters
warning shots for our climate future?

That is not included in climate models.

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

What new dangers lurk beneath

this vast frozen landscape?

And could they warm
our planet even further?

"Arctic Sinkholes."

Right now, on "NOVA."

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.

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

I actually thought it
was a made-up story.

Believe
me, I remember this date,

and I will remember it forever,

because it was
absolutely exciting,

something I have
never seen before.

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.

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.

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

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.

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.

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.

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.

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.

When combined with
air, it ignites easily.

So this is huge bomb.

Methane bomb.

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.

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.

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.

Look, there's
the lake right there!

Man, that's exciting!

Far from the
nearest town lies Esieh Lake.

Field technician Phil
Hanke proceeds cautiously,

hoping to avoid surprises.

Hey, bear!

Hey, bear!

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.

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.

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.

If you fly low
enough, even from the air,

you can see the bubbling.

It's just mysterious.

It looks like a Jacuzzi.

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

Like, the water is
boiling around you.

On their first visit,
the team wanted to investigate,

what's causing the bubbles?

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.

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.

This is the highest flux

methane seep that humans
have discovered in the Arctic.

The amount of methane
you see is staggering.

From the
shore, it's difficult to see

where the methane
is coming from.

So the team decides to
get closer to the source.

Hypothermia is
obviously the main danger.

Second is me getting air.

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

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.

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.

That gets deep so quickly.

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

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

Sullivan finds the
methane bubbles are streaming up

from the hole in the lake floor.

The bubbling,

it, it sounded like seeping gas,

as if it was even
from a propane tank.

How'd it go?

Still going
down! - Wow.

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?

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.

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.

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.

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.

This forest
sits on top of permafrost.

Scientist Tom Douglas
has been tracking some

surprising changes taking place

as the permafrost
starts to thaw.

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.

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.

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."

If you point that way,

that's Greenland over there.

Canada is over here.

And that way is, guess what.

Russia.

Gordon Brower

is a Native Alaskan
Inupiaq whaling captain.

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

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.

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

seals, whales, belugas,

ducks, geese,

caribou, wolves...

All of those are still
traded and used.

With little fresh food available

in winter, generations of Native
Alaskans have depended on

cellars carved out
of the permafrost.

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.

But thawing permafrost
means this natural deep freeze

isn't as cold as it used to be.

As Brower discovered.

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.

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.

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.

Exposed by the storms,

permafrost is thawing
and crumbling away.

Now communities like Utqiagvik

are trying to
protect their homes.

These are all

our local efforts to
stop the storm surge.

This is our way of
trying to save the town.

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.

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.

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?

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.

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.

The tunnel
reveals that permafrost contains

vast quantities
of organic matter.

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.

This ancient organic matter,

like all life on our
planet, contains carbon.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Unfortunately,

a lot of these Earth
system models

that contribute to such goals

do not take into account
CO2 and methane emissions

from permafrost.

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.

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.

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?

Good dogs!

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

Fairbanks, Interior Alaska.

Ecologist Katey Walter Anthony

is heading out onto
the frozen terrain.

Haw! Haw!

Come on, Biggy, come on.

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.

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...

That got me.

Oh, shoot.

Am I on fire?

No... I was wondering.

What's smoking?

You okay?

Yeah, I'm fine.

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

All right.

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.

The lakes
then start releasing methane.

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.

Positive feedback cycles

from permafrost regions

are another scenario not
sufficiently accounted for

in current climate models.

As permafrost thaws,

greenhouse gases
like CO2 and methane

will be released back to
the atmosphere much faster.

Warming is causing more warming.

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.

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.

Looking up
at the peaks around here,

and studying the local geology,

we know that this is

a highly fractured
and faulted region.

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.

I'm essentially
scanning the permafrost

using a geophysical method
called Very Low Frequency.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

Batagaika
reveals how a small human impact

can start a devastating
feedback cycle in permafrost.

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.

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.

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.

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.

Before,

it was more or less flat area,

but then ice melts

and surface subsides.

Romanovsky believes

lakes formed by
melting permafrost ice

have passed a
point of no return.

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.

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.

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.

Native
Alaskan Inupiaq Lars Nelson

is an infrastructure consultant.

He knows firsthand

what permafrost thaw is
doing to his community.

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.

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

In downtown Utqiagvik,

Nelson meets Inupiaq
Anthony Edwardsen.

These ones are subsiding, too.

Yeah.

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...

That's
where the houses are sinking.

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.

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.

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.

But as the
permafrost continues to thaw,

others in Alaska are looking
at more drastic solutions.

So this
is our portable, adjustable,

sled-base home.

It is on a giant steel sled,

as opposed to the pilings.

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

has a more radical
plan for sinking homes.

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.

As temperatures rise,

Hagle is searching for ways

to protect some of the
most isolated communities

in the United States.

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.

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.

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.

We've been whaling here

well over 4,000 years.

We've adapted
time and time again.

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

But the big thaw
is not just a regional problem.

What's happening in the
Arctic could really affect

everyone on Earth.

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.

Because it's very
difficult to take control

over the natural systems,

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

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.