♪ ♪ ♪ ♪ (woman vocalizing) NARRATOR: The Arctic.

Its vast frozen ocean cools our planet and impacts weather around the globe.

But the Arctic is changing-- warming at least twice as fast as the rest of the planet.

Exactly what's happening, and how it will affect life on Earth, has not been fully explored.

♪ ♪ ♪ ♪ But now, a global team of scientists is setting out on the biggest polar expedition ever attempted.

♪ ♪ MARKUS REX: We have hundreds of people from 37 different nationalities on board.

It's a massive operation on a scale that we have never seen in the Arctic before.

(machine whirring) ALLISON FONG: We're creating a benchmark of measurements that we may never be able to repeat in the future because there won't be sea ice for us to study.

NARRATOR: The plan is a world first: to take a high-tech research icebreaker and freeze it into the Central Arctic ice for an entire year.

MATTHEW SHUPE: We're taking a whole new level of sophistication with us.

All right?

Onboard the ship will be instruments that have never been installed in the Central Arctic.

NARRATOR: Locked in place, they'll explore every aspect of the Central Arctic as never before, through the constant darkness of a polar winter and some of the harshest conditions on Earth.

Their mission: to investigate why the ice is melting so fast and help us better predict how its rapid change will impact the rest of our planet.

It's about taking stock of what we've done to the Earth... ...and what we can still do.

(women vocalizing) NARRATOR: "Arctic Drift," right now, on "NOVA."

♪ ♪ (birds squawking) ♪ ♪ NARRATOR: After more than ten years of planning, an international team of scientists is heading north on the journey of a lifetime.

♪ ♪ FONG: This mission is the modern climate science equivalent of going to the moon.

♪ ♪ If you asked me if I'd ever imagined myself working in the Arctic, going to polar bear safety training, handling a rifle, I would have laughed at you.

I would have been, like, "You're crazy, there's no way!"

VISHNU NANDAN: Coming from a place where people have never seen snow or ice for the past thousands of years, Arctic, for me, is something out of this world.

The expedition will definitely give us a new perspective about the changes happening in the Arctic environment.

♪ ♪ SHUPE: Making scientific observations in the Arctic is very difficult.

Relative to the rest of the globe, we have very few observations of the Arctic system, especially in the wintertime.

We're going into a frontier, really.

I mean, the Arctic is still a frontier.

♪ ♪ (indistinct chatter) NARRATOR: The mission, dubbed MOSAiC, and led by Germany's polar institute, is heading deep into the Arctic sea ice.

♪ ♪ A place like nowhere else on Earth.

A vast, frozen world floating on a deep ocean.

It's thin and treacherous in summer, and almost impenetrable in winter.

It means the Central Arctic remains one of the least understood places on the planet.

But now, the team plans to establish a cutting-edge research camp by allowing their icebreaker, the Polarstern, to become frozen into the ice itself.

♪ ♪ (indistinct chatter) SHUPE: This looks great, I think, as far as size.

We're going into the sea ice to try to find an ice floe.

An ice floe is a discrete chunk of ice.

It's maybe a couple of kilometers across.

Ideally, our floe will be thick enough so that it can support all of our equipment that we want to put out on the ice.

And yeah, this stuff that's right there is the rotten layer that's underneath... (indistinct chatter) SHUPE (voiceover): And this will be our home for the next year.

So this is really a crucial moment in our whole expedition.

♪ ♪ NARRATOR: The success of the mission depends on taking advantage of a natural phenomenon.

♪ ♪ The plan is to hitch a ride on the Transpolar Drift, a constantly moving belt of sea ice that's driven by prevailing winds and ocean currents.

If they freeze-in near Russia, it should carry them for hundreds of miles-- close to the North Pole, then towards the Atlantic.

SHUPE: If we pick the right ice floe, then we'll stay in the ice pack for a full year.

If we pick the wrong ice floe, it might drift out to the ice edge faster than we anticipated.

It might break up.

And so we're walking a thin line here.

MAN (over radio): So we are standing by.

Copy that, I will take off now.

Okay, door's closed.

♪ ♪ NARRATOR: The team has spotted several potential ice floes.

(radio chatter) To find out if they're suitable, they need to explore them on foot.

(drill whirring) (Rex speaking German) MAN (in German): REX (voiceover): Our dream would be an ice floe that is thicker than one meter 20.

Just a stable island of ice.

MAN (in German): (speaking German): NARRATOR: The team searches for days.

REX (in German): NARRATOR: But the ice floes are all too thin.

They're running out of options.

SHUPE: This, this is interesting.

This whole area here looks... somewhat.... REX: Yeah.

SHUPE: We'll look over here.

See what we can find.

Yup.

NARRATOR: Eventually, they spot a floe that looks like it could be thicker.

So it first goes out 50 meters that way, and then we go, try to walk parallel to Polarstern over there.

SHUPE: There are quite a few potential hazards out there.

How thick is the ice?

Is it stable?

Is it safe?

REX: Matt, this is Markus, Matt, this is Markus.

SHUPE (over radio): Markus-- Matt.

I think our, our thinnest ice was 70 centimeters, and we've seen some up to multiple meters.

And there's quite an extensive area of that thicker ice.

REX: All right, Matt, thanks.

That sounds great.

NARRATOR: After days of uncertainty, it's an enormous relief.

♪ ♪ They've found their ice floe.

Now, as the ice starts to freeze around the ship... ...the real work can begin.

♪ ♪ (helicopter whirring) (indistinct chatter) NARRATOR: The team needs to unload around a hundred tons of equipment and set up bases out on the ice.

With just days remaining before the perpetual darkness of Arctic winter arrives, the pressure's on.

FONG: Every day, we're looking out the window and light is diminishing.

And it's a race against time.

(snowmobile running) NARRATOR: The plan is to build five research stations they call ice cities up to a half-mile from the ship.

♪ ♪ The cities and their cutting-edge equipment will allow scientists to explore every aspect of the Central Arctic at the same time, and crucially, constantly monitor how each piece of this complex puzzle affects all the others, from high in the atmosphere to the ice and the deep oceans beneath.

A mile-and-a-half of data cables and over three miles of power lines connect the cities to the Polarstern.

Beyond is a network of more distant science sites, as well as almost 250 remote monitoring stations.

The entire operation stretches across an area of around two-and-a-half thousand square miles.

♪ ♪ (wind howling) While the scientists work, others keep watch.

There's one thing they're all concerned about.

(ship horn blows) ESTHER HORVATH (voiceover): I'm standing there on this small hill at Met City, on my very first polar bear guard duty.

MAN (over radio): Bridge, bridge-- pack your stuff together.

You have to evacuate.

HORVATH (voiceover): Suddenly, I hear from the bridge two polar bears are approaching us.

They are 1,000 meter away, 900 meter away, and we all have to go back immediately.

In that second, I start to shout... (in scene): Stop doing what you're doing and come to the Ski-Doo!

(voiceover): Polar bears, if they are hungry, they would hunt for a person.

♪ ♪ REX (voiceover): These huge animals can reach speeds of 40 kilometers per hour, and everybody has to have that in mind.

Once a polar bear is close, it can be at the person in seconds.

(ship horn blowing) HORVATH (voiceover): I am the only person who have a rifle, and am I going to be able to use it, protecting all the people around me?

And that's a lot of people there.

SHUPE (on radio): Bridge, bridge-- Matt.

We are actually really full here.

We are going to try to load everybody on these.

It's going to be really full, but we'll try to make it out with what we have here.

(ship horn blowing) Guys, hurry up!

HORVATH (voiceover): In my mind, I don't care how small the sleds are-- everybody has to fit.

We all have to go back now.

♪ ♪ ♪ ♪ As we all got on board... GAUTE (over radio): Bridge, bridge, this is Gaute, over.

HORVATH (voiceover): That was when I saw them.

MAN (over radio): This is bridge.

GAUTE: Polar bear are at a hundred meters.

MAN: I will inform you when you have the shot with the flare guns, yeah?

Where is Trude?

She is right next to me.

The main goal is to have everyone safe and then scare the polar bears away.

We are invading their space.

(flares popping) I don't want to harm them.

(flares popping) So it is so nice when they understand that we are making too much noise for them.

(wind howling) NARRATOR: The darkness of Arctic winter arrives.

The team will not see the sun again for almost five months.

♪ ♪ (camera shutter clicks) HORVATH: It's an incredible experience to live, exist, and work here in the wintertime.

(shutter clicks) (shutter clicking) It looks unreal.

♪ ♪ It feels like we are somewhere else in the universe, this is not the Earth, this is something completely different.

♪ ♪ FONG: The darkness?

Working in the dark for months on end, not really being able to see beyond where your head lamp shines?

That's scary.

Yeah, that's pretty scary.

♪ ♪ NARRATOR: After three weeks on the ice, one of the most complex research camps, Met City, is up and running.

All systems green.

The tower is alive today.

(people speaking on radio) Our tower here is about 11 meters tall, and this can tell us about the turbulent exchange of heat, of energy, of moisture at the surface.

NARRATOR: Such detailed data has never been captured year-round in the Central Arctic before.

SHUPE: We need to understand what the sea ice is experiencing and how that affects the melting of the sea ice or the freezing of the sea ice.

The Arctic ice is melting, it's retreating, and we want to understand why that ice is changing.

NARRATOR: Today, sea ice in the summertime covers only half the area it did just 40 years ago, and the decline is accelerating.

Only some of the reasons are known.

♪ ♪ SHUPE: Decades ago, when there was more extensive ice cover, a lot of the sunlight that comes in in the summertime would just reflect back off that really bright, white surface and go back to space.

Now we have progressively less and less sea ice, and that exposes more ocean.

And that open ocean is dark.

It absorbs the sunlight, and therefore warms up the ocean and melts even more ice.

NARRATOR: This feedback loop is a major reason why the Arctic is now warming at least twice as fast as the rest of the planet.

♪ ♪ But it's not the only factor.

Already, Met City is shedding new light on another potentially powerful warming influence.

SHUPE: Clouds are a big player in the Arctic system, as they are in the whole global system.

On the one hand, they shade the surface from the sun, right?

So they cool the surface.

On the other hand, they serve as a blanket and they trap the energy at the Earth's surface.

And it gets really interesting in the Arctic, because during parts of the year, there is no sun.

It's dark for four months straight.

And so the clouds are only serving as a blanket.

(wind howling) What we're seeing is that in polar winter, there's actually a lot more thick cloud than I expected.

It's slowing the winter sea ice growth.

That means less ice going into spring and summer, which in turn makes it more vulnerable to the melting season.

NARRATOR: The clouds are one piece of the complex puzzle the expedition is trying to put together.

♪ ♪ Another is the hidden world under the ice.

FONG: It doesn't look like much, I mean, right, at the surface?

You're, like, it's just snow, it's quiet.

But actually, below the ice, there's a flurry of activity.

(chainsaw revving) I'm used to making lab experiments with a pipetter and-- delicate work.

(chainsaw revving) And here I am with a 60-centimeter-long chainsaw.

(chainsaw stops) (indistinct chatter) ♪ ♪ Some of the big outstanding questions are, what are the activities of organisms in polar night?

From the Central Arctic, there are basically no measurements whatsoever.

So this would be the first chance in history for us to do that work.

♪ ♪ NARRATOR: This device can collect water samples at specific depths, down to just above the ocean floor... MAN (speaking German): NARRATOR: ...two-and-a-half miles below.

♪ ♪ WOMAN: What?

FONG: At this place in the world, at this time of year, there's never been data like this.

And that's incredible, and so every time we put a piece of equipment out and we collect a sample successfully, we're the only people that have been able to do it.

FONG: Okay, so Jien, you're done for D.I.C.

on one.

Uh, Haylun, that means you can do salinity on number one.

NARRATOR: What they're finding is a huge surprise.

FONG (voiceover): I think winter in general is thought of as a time of hibernation or low metabolic activity.

But what we're seeing is that organisms have adapted over millennia to this, what we consider an extreme environment.

♪ ♪ In one milliliter of seawater, which is basically, like, a teaspoon of seawater, are one million bacterial cells.

And from there, the diversity is extraordinary.

NARRATOR: The team finds that phytoplankton, plant-like organisms that rely on the sun for their energy, are still present in winter, primed and ready for spring.

They also discover tiny zooplankton in their thousands-- far more abundant and active than they'd imagined.

♪ ♪ This thriving ecosystem is vital for our planet.

Globally, phytoplankton produce around half the oxygen we breathe and absorb vast amounts of carbon dioxide, while the zooplankton that feed on them help lock that carbon away in the depths.

It's partly why the oceans absorb around a quarter of the CO2 produced by the burning of fossil fuels.

For our climate, these tiny creatures play a crucial role.

FONG: Given that the Arctic is experiencing so much change, we need to understand what impact reductions in sea ice and global warming is having on these organisms and how these components of the climate interact.

NARRATOR: Almost two months into their yearlong mission, the Transpolar Drift has carried the Polarstern over a hundred miles deeper into the Arctic.

HOHLE (over radio): Bridge, bridge, Trude.

Trude, go ahead.

HOHLE: I'm in position, stern.

Thank you, enjoy your watch.

(snowmobile engine humming) HOHLE: Do we have a ladder here?

(wind howling, snow crunching) (people speaking on radio) HOHLE: (bleep).

Oh, my God.

(ice rumbling) The ice is moving a lot.

Bridge, bridge, for your information, the ice here has really started to move.

We noticed by the sound and are monitoring it now.

We managed to save the ladder, which is now on our side.

(ice rumbling and creaking) HORVATH: It's so loud.

It sounds like a, an engine as it starts.

(voiceover): It is like an earthquake under your feet, but there is nowhere to run.

You really feel how fragile you are.

It's a frightening experience.

HOHLE: Let's hope we find a way over.

(rumbling stops) Oh, it's stopped.

Bridge, bridge, Trude.

MAN (over radio): Go ahead, Trude.

HOHLE: Ice has stopped moving and it's completely silent here in the Arctic again.

SHUPE: This is stress on the ice.

This is the winds and the currents in the ocean causing pressure in the ice, and eventually, the ice just lets go.

There's internal pressure and it breaks.

(radio chatter) (wind howling) NARRATOR: And those stresses are intensified by the arrival of a violent storm.

(wind howling) Cracks in the ice open up, some big enough to wreck the entire base.

HANS HANOLD: There is one crack behind Met City.

We've lost the power, huh?

Yeah.

SHUPE: It's knocked out our power supply.

It's taken down our measurements at Met City.

We have to get back out there.

We have to get the power hooked up again, so that we can continue making our measurements.

REX: Goal of operation, really, is to rescue the cables so that we don't lose them.

WOMAN: So we prepare the kayak?

REX: Yep.

All right!

(engine running) (wind roaring) WOMAN: All good?

Yeah.

Team Kayak?

(indistinct chatter) NARRATOR: The first thing they need to do is find out if the cable is still connected to the ice cities.

(wind roaring) WOMAN (over radio): All right, the connectors have been ripped off, so the other half is probably in the water.

We can't reach it, we can't see it.

MAN (over radio): Copy that.

NARRATOR: With the power cable hanging deep into the ocean, they'll need to retrieve it by hauling it out with a snowmobile.

HANOLD: Slowly, slowly!

Hey, stop, stop!

There is something else hanging here.

(speaks inaudibly) Yeah.

(snowmobile engine revs) Okay, we are very close.

Ah, this is the end.

This is the end.

(laughs) Well done, guys!

Excellent.

NARRATOR: With the cable saved, the team can restore power to the ice cities and get the science back up and running.

(wind howling) NANDAN: I don't know if I am the first Indian to walk on frozen ocean waters, but, at least, for this expedition, I am the only Indian.

My name is Vishnu Nandan.

♪ ♪ (indistinct chatter) Vishnu means preserver of the planet, and that's my goal.

I'm here to protect the planet.

To every, to protect everyone.

Let's pull it across.

We don't want to block the way with this.

Okay, yeah, I mean, we can at least bring the cables this direction.

JULIENNE STROEVE (voiceover): I've been going up to the Arctic region for almost 30 years now, but it's always been during daylight.

Doing it over winter, yeah, that's a really unique experience that many people, even if you're a scientist working in the Arctic, you don't get to experience that.

And honestly, you feel like you're walking on the moon.

STROEVE: That's amazing!

(radio chatter) Hi, fox!

That is very cool.

My first polar fox.

That's exciting.

Yay.

Okay, check if my instrument's working now.

NARRATOR: Julienne and Vishnu are running the Remote Sensing City.

They're here to answer one of the most fundamental questions of all: Just how much ice is in the Arctic Ocean?

♪ ♪ STROEVE: We have over 40 years of satellite measurements telling us how much of the Arctic Ocean is covered by sea ice, but what we've really lacked is knowing how thick the ice is.

NARRATOR: The problem is that satellites can't differentiate between the ice and what's just snow on top of it.

By testing the same technology at the surface, where they can compare the results against physical measurements, they hope to revolutionize our ability to monitor sea ice from space.

STROEVE: It would allow us to actually map not just the spatial extent of the ice, but the actual ice volume in the Arctic every single day.

NARRATOR: As they begin to analyze their results, it confirms what they suspected: satellites have been vastly overestimating ice thickness.

It will take time to turn their data into new, more accurate predictions, but it's a major breakthrough.

STROEVE: Collecting the data is really key, and will hopefully help the public and policymakers understand how quickly the Arctic is transforming and that we need to do something before it's too late.

(wind howling) NARRATOR: As a new year begins, the team is less than 200 miles from the North Pole.

♪ ♪ They're due to receive vital supplies, equipment, and a new team of scientists before the ice becomes too thick to reach them.

But the Russian icebreaker entrusted with the task is hundreds of miles away, struggling through thick ice.

(clicks mouse and key) AMY MACFARLANE: As soon as the icebreaker started to move through the ice, I got the sense of how remote the area we're going to is.

I mean, we're traveling for weeks to get to this miraculous haven in the north.

(ice churning) NARRATOR: No icebreaker has ever tried to venture so far north in the middle of winter before.

(ice churning, crunching) (metal clanging) (ship stops) ALEXANDR ERPULEV (speaking Russian): ♪ ♪ (ice churning) (metal clanging) ♪ ♪ NARRATOR: If the supply ship has to turn back, the team here could be stranded for months, and they'll be dangerously low on fuel for heat and power.

It's affecting the morale of the scientists onboard.

We are kind of stuck here.

♪ ♪ (wind howling) (indistinct chatter) MAN (on radio): There, there to the east.

Is that the Dranitsyn?

♪ ♪ NARRATOR: After a grueling monthlong journey, and with the first signs of sun returning, the supply ship, Dranitsyn, finally makes it.

♪ ♪ (indistinct chatter) Okay, team, we walk.

And we follow them.

MACFARLANE: At one point, I didn't think we'd be here.

But it's happened.

It's incredible.

♪ ♪ NARRATOR: With the new scientists and supplies on board, the mission is back on track.

♪ ♪ (wind howling) ♪ ♪ NARRATOR: As the sun returns, the Arctic begins to transform once again.

For the scientists, it brings a whole new world to explore.

♪ ♪ Welcome to the office.

♪ ♪ MACFARLANE: For me, snow tells a story.

We're trying to understand, in this scale, how it's changing, and eventually link it to the whole of the Arctic snowpack.

We start one snowflake at a time.

♪ ♪ So at the surface today, we have -20 degrees.

But then just 17 centimeters below, we have minus nine degrees.

So it has a really big influence.

(sniffs): Oh!

NARRATOR: The snow here is acting as a major insulator, trapping heat from the warm ocean in the ice and slowing its escape to the atmosphere.

With scientists predicting that a warming Arctic will see more precipitation, which means more snowfall, understanding why it's having such a dramatic effect is crucial.

Using a CT scanner, the team can study the structure of Arctic snow in minute detail.

MACFARLANE: So, at the top, these are all really compact and tightly together.

And then as you move further down, you come across these large crystals.

I've never seen these crystals quite so big before.

You can start to see more and more air.

The blue would be an air gap.

♪ ♪ NARRATOR: The scans reveal how during winter and early spring, large crystals in the snow trap more air, keeping the ice warm and inhibiting the growth of new ice.

This may seem strange, but under certain conditions, more snow can mean less sea ice.

The Arctic is now in full transition.

With just over two weeks between first sunrise and 24-hour daylight, every day there's more opportunity for one team to take to the skies.

JOHN CASSANO: Let's do this.

GINA JOZEF: Let's do it!

Three, two, one, go!

(whirring) Hell, yeah!

Whooo!

CASSANO: Way to go, team drone.

JOZEF (laughing): We did it, whooo!

First flight, success!

CASSANO: The plane will spiral up from near the surface up to 1,000 meters.

And we're measuring the state of the atmosphere, so that's the temperature, pressure, humidity, and wind.

It is flying really well.

I am so happy.

NARRATOR: And right away, there are exciting findings.

JOZEF: Here we have a plot of the temperature, and the wind speed.

Yeah.

And you can see that we have a really strong inversion in the temperature around 200 to 300 meters, or... CASSANO: The first flight we did had this real sharp temperature inversion, where the temperature increases with height.

It's the opposite of what we normally see where we live.

NARRATOR: This phenomenon, characteristic of the poles, is caused by the icy surface cooling the air just above it.

CASSANO: What's interesting to me is that the temperature inversions are often associated with this core of really fast winds right near the surface of the Earth, where sea ice or ocean or snow exchange energy and moisture and different gases.

And so the wind is really a critical part of understanding how the atmosphere is coupled to these other parts of the climate system.

NARRATOR Along with these crucial surface winds, there are other polar winds, much higher, that have a powerful effect on the climate far beyond the Arctic.

The jet stream is a band of high-altitude wind that whistles around our planet at over 100 miles an hour, influencing much of the weather in the Northern Hemisphere.

It's driven by the temperature difference between the warm Equator and cold Arctic.

Many scientists think the faster-warming Arctic may be weakening the jet stream, causing it to become unstable.

It's a controversial theory, but if true, it could have catastrophic results.

Cold air is able to escape out of the Arctic and cover parts of Europe or North America and give us really cold winter weather.

Or if the jet stream pushes very far north, and you get these intrusions of warm air up into the Arctic.

(thunder rumbling) NARRATOR: The weaker jet stream might also be causing weather patterns to get stuck over the same area for longer, prolonging droughts and floods.

CASSANO: It impacts everything we do.

It impacts farmers and where they can grow crops, where rain falls, how often droughts occur, how often heat waves occur, how often blizzards occur-- I mean, all of the weather that we experience.

NARRATOR: In addition to altering weather patterns in the Northern Hemisphere, the warming Arctic is also speeding up global warming, which will affect weather everywhere.

And as ice on land also melts faster, it accelerates global sea level rise.

What happens in the Arctic affects us all.

CASSANO: The Arctic is far away.

You know, 'cause you think, "Oh, it's so far away, who cares?"

But it has such a critical impact on the, the global environment that we all have to care.

♪ ♪ NARRATOR: Six months in, the Transpolar Drift is carrying the Polarstern and its ice cities around eight miles each day, as the rest of the world faces a pandemic.

BORIS JOHNSON: The coronavirus is the biggest threat this country has faced for decades.

All over the world, we are seeing the devastating impact of this invisible killer.

♪ ♪ NARRATOR: The scientists may be more isolated than anyone else on Earth, but as spring turns to summer, they face their own challenges.

The thinning ice is increasingly treacherous.

Large cracks form, and huge ridges of colliding ice bury equipment.

Both are made worse by violent storms.

And as they drift ever closer towards the edge of the ice pack, the favored hunting ground for bears, their work is constantly interrupted.

(clanging) (growling) (ship horn blaring) By mid-June, much of the Arctic is in the grip of a record-breaking heat wave.

In July, the ice is disappearing fast, leading to the smallest area of Arctic sea ice ever recorded for this time of year.

The question on everyone's mind is, how long will their ice floe last?

MACFARLANE: So this one, can you see it?

It's kind of... WOMAN: Ooh, yeah, yeah.

There's a few, like, lines.

This is undergoing melting.

Yes, I see.

MACFARLANE: The water in the snow, it's just trickling down and pooling on the ice.

And the ice starts to become, we call it rotten.

The processes and changes have been really quick, a lot quicker than I, I thought they were gonna be.

So, how long have we got?

(laughing): That's a good question.

(dripping) NARRATOR: While the floe is becoming increasingly fragile, the thinner ice is also moving faster than expected.

The team had hoped to stay locked in until September, but by mid-July, the Transpolar Drift has already brought them close to the ice edge, where the waves of the open ocean will finally destroy their floe.

♪ ♪ SHUPE: It could be a very dangerous situation, where the ice floe breaks into small pieces.

It could be any day now.

FONG: You know, sea ice, it has a lifetime of its own, and so we watched it grow when we arrived, and now we're watching it decay.

(dripping) (woman vocalizing) REX: Good morning, everybody.

We are at a distance of nine nautical miles from the ice edge, and that is the distance where we need to take things down.

It's time to say goodbye to our research camp.

(applause) ♪ ♪ (drill whirring) SHUPE: We measured right up to the end, and actually, that feels great.

♪ ♪ To me, this feels like a huge accomplishment.

♪ ♪ (woman speaking on radio) FONG: So, I wake up, and I go to the bridge... (radio chatter) ...and there's nothing.

SHUPE: Our floe is gone.

It's totally gone.

It's disintegrated into a thousand pieces.

♪ ♪ FONG: Overnight, we went from having a floe that we could work on, that we were moving heavy equipment on, to literally shambles of ice.

It was incredible.

(woman vocalizing) NARRATOR: Soon after their ice floe melts away into the ocean, 2020 is confirmed as having the second-smallest extent of summer sea ice on record.

Across the Arctic, vast areas are ice-free.

♪ ♪ There are even patches of open water at the North Pole itself.

♪ ♪ STROEVE: We don't have that much time left.

If the Arctic Ocean is going to lose its summer sea ice, that's a big climate shift.

CASSANO: The problem is that climate change is this gradual, creeping change.

I think eventually, we're going to cross a, a threshold where the weather and the climate become so different from what we're able to deal with, that it will become a crisis.

That it will become urgent, like COVID has been for us.

FONG: Here's the question I would like to pose: why not act now?

♪ ♪ CASSANO: Humans are very resilient, we're very innovative.

We can come up with ways to solve this, but we need to start working together more than we are.

♪ ♪ MOSAiC is a symbol of what we need to deal with, the challenges we face.

It's a global problem.

And you solve global problems by acting as a global community.

(helicopter blades chopping) SHUPE: We're leaving the Arctic now with a tremendous amount of new knowledge, and it's going to be available for everyone around the world to use.

MACFARLANE: What each team has found has been really extraordinary.

The implications are huge.

♪ ♪ NARRATOR: From thousands of feet above the Arctic ice to the ocean deep below it, the team has gathered more than 150 terabytes of vital new data and countless samples still to be examined.

As scientists around the world work together to analyze and combine the findings, they'll piece together a new picture of our changing Arctic, transforming how we see our future and what can be done about it.

♪ ♪ FONG: The world is changing, and there is something that we can do about it, but it takes us making better choices about our everyday lives.

I hope that what you've seen encourages you to believe that, as we continue to be curious about our world, it will help us protect it.

♪ ♪ What is at stake?

Everything, I would say.

♪ ♪ ♪ ♪ ♪ ♪ ♪ ♪ ♪ ♪ ♪ ♪