NICK SCHIFRIN: Finally from us: melting ice.

The world's glaciers are receding at an alarming rate, losing more than a trillion tons of ice a year.

It's fueled in part by climate change and is driving sea levels higher, which could threaten coastal communities around the world.

Special correspondent Ben Tracy of Climate Central found a man who, alongside his family, has seen the melt firsthand every year for nearly half-a-century.

BEN TRACY: But it is stunningly beautiful out here.

MAURI PELTO, Glaciologist, Nichols College: This one, two miles we have done so far today, I mean, that was fun.

BEN TRACY: I'm not complaining.

I'm happy to take a walk in a glacier any day.

In the rugged North Cascade Mountains of Washington state... MAURI PELTO: ... my life has been shaped by this ice.

BEN TRACY: ... no one likely knows this glacier better than Mauri Pelto.

MAURI PELTO: We got 6,000 measurements on this glacier.

BEN TRACY: You have 6,000 measurements on this one glacier?

MAURI PELTO: Yes, at least.

BEN TRACY: Wow.

For more than 40 years, Pelto, a glaciologist, has returned to this remote wilderness, the crunch of footsteps in the snow now rivaled by the sounds of melting ice.

MAURI PELTO: It's always melting off.

The crevasses are changing.

We could hear the water flowing under our feet.

BEN TRACY: Yes, I mean, just standing here, you can hear it just running under our feet.

MAURI PELTO: Yes.

BEN TRACY: Pelto founded the North Cascades Glacier Climate Project in 1984 as a grad student.

He vowed to measure these glaciers every summer for 50 years.

So how deep is that?

MAURI PELTO: This is 9.5 feet.

So now we just do this over and over again all day long.

BEN TRACY: This is year 42.

How old were you when you decided to do 50 years of this?

MAURI PELTO: I was 22.

BEN TRACY: Twenty-two.

How old are you now?

MAURI PELTO: Sixty-three.

BEN TRACY: In that time, the glaciers have changed more than he has, shrinking by 40 percent.

Some have disappeared.

Pelto's work has been featured by NASA and fed into a worldwide glacier database.

So, of the 47 that you have studied and returned to over and over again, how many are gone?

MAURI PELTO: Twelve of them.

BEN TRACY: Twelve?

MAURI PELTO: Yes, and nine of them just in the last five years.

BEN TRACY: Wow.

Climate scientists say warmer summers and drier winters driven by our burning of fossil fuels are accelerating the loss.

Seven of the 10 worst years for glacier melt worldwide have happened since 2010, according to Climate Central.

Or just ask Mauri Pelto where the ice used to be.

MAURI PELTO: Almost 50 feet above my head just a decade ago.

BEN TRACY: A decade ago, this glacier would have been 50 feet above your head?

MAURI PELTO: Yes.

BEN TRACY: That much has been lost?

MAURI PELTO: Yes.

BEN TRACY: Glaciers are Earth's water towers, storing 70 percent of the fresh water supply, vital for drinking, farming and the health of many ecosystems.

As they melt, sea levels are rising and coastal flooding is getting worse.

MAURI PELTO: We're on Ptarmigan Ridge.

And that's a ridge that extends most away from Mount Shuksan to Mount Baker that we're looking at.

BEN TRACY: That is spectacular scenery up there.

MAURI PELTO: It is.

It's the highest mountain in the North Cascades.

BEN TRACY: On his annual treks to Mount Baker... MAURI PELTO: ... it feels like home.

BEN TRACY: ... Pelto has hiked nearly 6,000 miles and slept 800 nights in a tent.

MAURI PELTO: This is our kitchen.

We got our living rooms.

We got our picture window.

It's also one of those places that's really special to us as a family.

BEN TRACY: His son Ben, daughter Jill and now his 9-month old granddaughter Wren have joined him in the field.

JILL PELTO, Artist: Two feet.

MAURI PELTO: Two feet.

BEN TRACY: Jill Pelto has spent 17 summers by her dad's side.

MAURI PELTO: I get some measurements of the GPS along the blue ice.

BEN TRACY: But she doesn't just collect data.

As the project's art director, she paints it.

So these measurements that you and your dad are taking out here, eventually, some of those data points will go into your art.

JILL PELTO: Yes, exactly.

Data is a story about something in the real world, and that story has meaning and emotion.

And that's what I'm trying to bring into my art.

BEN TRACY: Her watercolor paintings are more than just beautiful landscapes.

They reveal the science.

Look closely and you see a bar graph of glacier decline in the North Cascades.

One piece showing temperature rise and ice loss made the cover of "TIME" magazine.

JILL PELTO: I think sometimes, when people see data, there's kind of this instant reaction.

And so it's not like the data is any different in my art.

But something about that combination maybe gets people to kind of put down that wall of like, oh, I can't understand this or this is not something I'm interested in.

BEN TRACY: The average person is not going to read a scientific report.

JILL PELTO: No.

BEN TRACY: But they will see a painting.

JILL PELTO: Yes.

BEN TRACY: And it does impact you in a different way.

JILL PELTO: Yes, definitely.

BEN TRACY: Her art has given her dad a new way to share the story he's been recording for the past 42 years.

MAURI PELTO: There's nothing left of the glacier that was around that cave.

JILL PELTO: No.

BEN TRACY: What has this been like for the two of you to do this together?

I imagine something like this has to change your relationship in some way.

MAURI PELTO: We do it so seamlessly at this point, sometimes, I don't know what -- where I start and... (LAUGHTER) BEN TRACY: It feels like you're one team out here?

MAURI PELTO: Yes.

JILL PELTO: This bigger project, it just means so much to us and has shaped our lives.

So, sharing that every year is, yes, beyond special.

MAURI PELTO: Tomorrow, we go to the Rainbow Glacier.

BEN TRACY: And now Mauri Pelto has just eight summers left to fulfill his 50-year promise.

What do you think it's going to be like that first year you don't come out here?

MAURI PELTO: I don't know.

I can't remember what it was like to not come out here.

This landscape has been shaped by ice.

And so to understand the landscape and the ice, you really have to walk across it.

BEN TRACY: For the "PBS News Hour," I'm Ben Tracy with Climate Central.