The following is a script from "Greenland," which aired on Jan. 31, 2016, and was rebroadcast on July 31, 2016. Sharyn Alfonsi is the correspondent. Daniel Ruetenik, producer.
One of the most significant efforts to study changes in the climate has been taking place near the top of the world. As we first reported earlier this year, it's a place called Petermann Glacier in Greenland, one of the largest glaciers in the Arctic Circle and a glacier that has experienced dramatic melting. It is a harsh and dangerous environment, and it has drawn some of the world's leading climate scientists who are only able to work there a little over a month a year. We wanted to see how that work is proceeding, how they are able to move equipment and people in such a hostile place and what they've discovered so far -- so we went to the top of the world to find out.
Our journey took us 700 miles above the Arctic Circle to the U.S.'s Thule Air Force Base in northern Greenland, built at the start of the Cold War to watch for Soviet missiles. It is an alien landscape, home to curious arctic hares and packs of prehistoric-looking muskox.
From there, we flew even further. The destination: Petermann Glacier. It's on the northwest coast of Greenland, just a few hundreds miles south of the North Pole.
To get there in a helicopter took us four hours over a rarely seen landscape that is both severe and serene.
The last town we'd see was Qaanaaq, with 700 residents and more huskies than people. Locked in by ice nine months of the year, villagers have always hunted seal and narwhal to survive.
Greenland is three times the size of Texas and 80 percent of it is covered in ice but it now loses more ice than it gains in snowfall every year.
We saw evidence of the imbalance everywhere. Blue gashes across the ice, rivers of rushing melt water and the occasional thunderous crack of icebergs dropping into the sea.
We still had 300 miles to go and stopped twice to refuel along the way. These barrels were left behind for us by the scientists who made the trip to Petermann Glacier three weeks earlier.
Sharyn Alfonsi: This is the ultimate self-service gas station in the middle of nowhere. This will keep us going for how much longer?
Malik Jensen: Yeah we can fly two and a half hours.
Our pilots, native Greenlanders, kept a rifle nearby at each stop to protect us from polar bears.
Sharyn Alfonsi: Have you seen polar bears out here?
Malik Jensen: Yeah, a lot. So now it's ready, always safe.
Finally we arrived at Petermann Glacier and spotted the ice camp below.
Alan Mix: Great to see ya.
Sharyn Alfonsi: So who did you upset to get put out here?
Keith Nicholls: I know. The gods, the gods.
Keith Nicholls is an expert in drilling in remote places and in terms of remote, this would be really hard to beat.
Sharyn Alfonsi: It feels like you're on another planet.
Keith Nicholls: Take a walk around here and you can be expecting Scotty to beam you up. It is extraordinary.
Nicholls and a team of scientists were drawn to this remote sliver of Greenland, in part, by these satellite images.
In 2010, a chunk of ice -- four times the size of Manhattan -- broke off. Then, two years later, another large chunk came down.
The glacier has receded by 20 miles in five years. Nicholls and his team are trying to drill beneath it.
Sharyn Alfonsi: This is a lot of work in difficult conditions. What do you hope to learn?
Keith Nicholls: What we're trying to learn is how the oceans are interacting with the ice, how they are melting it trying to predict how in the future that melting might change.
To drill through the ice they heated melt water from the glacier to make a hot water drill to pierce through the 300-foot thick ice.
Sharyn Alfonsi: There has to be serious challenges to running equipment like this in this kind of weather.
Keith Nichols: The biggest challenge is that we've got water and it's very cold. So if we have water freezing in hoses that can be devastating for the project.
This is the moment the coring machine struck the bottom of the seafloor. A half-mile beneath the ice, they made history. It was the first time anyone has ever collected sediment from beneath the ice shelf in Greenland.
Keith Nicholls: The ocean beneath the ice shelves is probably the least accessible part of the world's ocean. And just getting access to that is a triumph frankly. As far, as we're concerned.
The ice shelf extends out from the glacier and floats on the ocean. They believe it acts like a dam, holding back the ice from sliding into the sea. If it goes away, sea levels go up.
Sharyn Alfonsi: Is there a sense of urgency in the work that you're doing?
Keith Nicholls: Sea level rise is the big, the big question that we're trying to get at. And Petermann Glacier, this experiment here, gives us an opportunity to get at those processes and try to understand the basic physics as to how that can happen.
Our visit to the ice camp was cut short. Our pilots warned us something called "ice fog" was moving in and could strand us here for days. We high-tailed it back to the helicopter, heading to another outpost of the expedition -- what the scientists call "boulder camp," set up on the edge of Petermann Glacier.
Shaun Marcott and a team of geologists have been here for weeks, gathering samples from rocks.
Shaun Marcott: So, this was probably deposited when the ice was maybe a few hundred to a few thousand feet thicker, and when it was deposited, you're probably talking about-- maybe 500, 600 feet of ice above us.
Sharyn Alfonsi: Above where we are right now?
Shaun Marcott: Above where we are now. Peterman would've been much larger, and it would've been dropping these rocks all over the surface.
Sharyn Alfonsi: To the person at home who's looking at you guys just chipping away at rocks and going, why should I care about this?
Shaun Marcott: We know that if you warm the planet up, glaciers respond, they melt. The question is, at what rate? How fast is that gonna happen, and where is it gonna happen, and where are the most vulnerable spots in this ice sheet? To understand all of that, you have to understand how the ice sheet-- what controls an ice sheet?
Shaun Marcott: We need to understand this glacier, so that we can provide a better prediction for the larger ice sheet. That matters to us because of sea level. If these glaciers-- can respond dynamically, then we should all be concerned, because that can create dynamic changes in sea level and flood infrastructure. And we need to know that for planning for the future.
We camped out next to the scientists. With 24 hours of light, we slept in these tents under the midnight sun. In the morning we were shuttled out to meet the Oden, a Swedish ice breaker making its way around Petermann Glacier.
The Oden supports the scientists on land and acts as a floating laboratory. Named after a Norse god who relentlessly sought wisdom, it's home to more than 50 climate scientists from around the world with similar convictions. Their work is funded mostly by the Swedish government and the U.S.' National Science Foundation.
Larry Mayer is one of the geologists on the Oden. He's using sonar to map the ocean floor, creating the first detailed maps that show how Petermann Glacier slid into the sea. You can see it, like skid marks of a car at an accident scene.
Larry Mayer: "Oh yeah, the ice went here and the ice went there." And we can see it. "Oh and it stopped here."
Sharyn Alfonsi: How much of the world's oceans have been mapped with this kind of detail?
Larry Mayer: Oh, probably-- on the order of six percent to seven percent.
Sharyn Alfonsi: Six--
Larry Mayer: Very, very little. Yeah.
You can only make the trip to Petermann Glacier a few weeks each summer when the ice melts enough to allow passage.
Alan Mix: You can see those blocks of ice drifting by.
Expedition leader Alan Mix is running the ships coring operation, trying to grab sediment from the seafloor.
Alan Mix: So actually, the coring site right now is under that block of ice and we just can't get there. So we're trying to drift with the ice and just sort of sneak up on it gently.
It's hard to sneak up on anything in an ice breaker. The Oden doesn't so much as sail as it does smash the ice like a 13,000-ton hammer.
Once in position they throw something called a piston corer, like a dart, at the bottom of the ocean.
[Alan Mix: Oh, that doesn't sound good.]
After multiple attempts...
[Alan Mix:Go to the next one but we'll hit it with the gravity core.]
A core sample like this is collected inside the ships lab, the multi-year process of investigating those cores begins.
Sharyn Alfonsi: What's your best guess? How old is this?
Anne Jennings: So the base of this core probably is no more than 10 thousand years.
Anne Jennings is with the institute of Arctic and Alpine Research. She says each core holds clues about Petermann Glacier's past.
Anne Jennngs: Well, we didn't really expect to find things living under the ice shelf but we have.
Sharyn Alfonsi: What have you found?
Anne Jennings: This one we've found is called cibicidoides wuellerstorfi. It has a big name for a little bug.
Sharyn Alfonsi: Easy for you to say! It looks like a little seashell.
Anne Jennings: And it is a seashell but it is a single-celled animal.
That single-celled animal, like all living creatures, is made out of carbon allowing scientists to determine when it lived.
Sharyn Alfonsi: Which tells you what?
Anne Jennings: The age of the sediments. So we can take them the depth scale here and convert it to age. And then we can say, "When did the ice retreat? How quickly did it retreat? Was there a lot of melt water coming out?"
Sharyn Alfonsi: You can get all that from what looks like mud?
Anne Jennings: Yes.
After a week in Greenland, we headed home but the scientists kept working, taking advantage of the final days of the short Arctic summer.
The 66 core samples they collected during their month at sea will be studied by scientists around the world for decades.
Peter Demenocal: This is the largest core depository in the world.
Peter Demenocal is a paleoclimatologist at Columbia University. He says the cores collected in Greenland are like a black box of the Earth's inner workings. This one he collected just south of Greenland.
Peter Demenocal: So this is today's climate and we've had about 10,000 years of relatively warm climate. And then we go 10,000 years in the past -- boom, there's the last Ice Age. This is when Long Island was formed and Cape Cod was formed.
Peter Demoncal: And you can go on, and you can just find this color. It's filled with these rocks, what we call ice rafted detritus, until this period when -- whoa, there's another warm phase. And then another cold phase, and then another warm phase. A short, cold phase, a longer warm phase and then -- boom, another Ice Age. And so you've had cold, warm, cold, warm, cold, warm, today.
Sharyn Alfonsi: How do we know that the warming we're seeing now, how do we not know it's part of this warm, cold, warm, cold?
Peter Demenocal: That's a great question. These transitions are gradual. And kind of almost like a tide wave or something. And this transition, when you get to today, goes boom. Suddenly very warm.
Demenocal says the cores pulled from Petermann Glacier will fill in a crucial piece of the climate change puzzle.
Sharyn Alfonsi: How impressive was it that they got to Petermann Glacier?
Peter Demenocal: It's impressive. What's more impressive is that we haven't been there every year and that we're not going-- not doing this every year. We should be doing this-- we should be monitoring this whole system with much greater focus than we are now.
Sharyn Alfonsi: How quickly have we seen the changes in Greenland?
Peter Demenocal: The changes that are happening right now as a result of human activities are remarkable. And they're happening incredibly fast and they're-- it's not only happening fast but it's accelerating. And it's important to really get our mind around what we're saying there.
Peter Demenocal: We're not just saying that climate in the Arctic is changing. It's changing at an accelerating rate. So basically it means it's starting to melt but it's melting at a faster and faster clip. So anyone who knows what it's like to fall off a cliff, that's what it's doing.