Text Version

Melting Ice: Rising Seas

Video transcript
The video is 7 minutes and 6 seconds long.
Produced by the American Museum of Natural History, May 2007.

Video begins here.

Visual: Aerial views of fragmenting ice sheets floating on the ocean.

Speaker: Jonathan Overpeck, Institute for the Study of Planet Earth, University of Arizona

On Earth, we have a lot of water locked up as ice.  Particularly at the poles, you get really big piles of ice, and we call those ice sheets.  These ice sheets are great indicators of what's going on with our climate.  So, there's a lot of investigation: are they melting, are they not melting?

Visual: Jonathan Overpeck in office

Because if they do melt, they raise sea level, and that affects everybody in big ways.

Title: Melting Ice: Rising Seas

Visual: An aircraft propeller as seen through a plane’s window.  An ice sheet seen through a plane’s cockpit window.

Speaker: Aircraft crewman

That’s the edge of the glacier, right here. Co, go straight over the glacier right here.

Visual: The 109th Airlift Wing flight to Greenland. An airman sits in the aircraft with noise-reducing headphones on. Bob Hawley walks along the edge of a glacier.

Speaker: Bob Hawley, Department of Earth and Space Sciences, University of Washington

We're at the Russell Glacier, which is a small outlet glacier on the edge of the Greenland Ice Sheet.

Visual: The edge of the Russell Glacier.

A glacier is ice in motion. It’s flowing under its own weight.

Visual: Bob Hawley at the edge of the Russell Glacier

If you were to stand here with a camera, day after day, what you would see is the ice marching towards us and falling off, and falling off.

Visual: The edge of a glacier by the ocean.  Large chunks tumble into the sea.

When we say the Greenland Ice Sheet is melting, the way that happens is the outlet glaciers speed up.

Visual: A large portion of the glacier crashes into the sea.  Smaller chunks of ice float in the ocean.

And when the outlet glaciers speed up, more ice breaks off into the fjords.

Visual: An aerial view of the Greenland Ice Sheet

It’s not as if the entire surface of the Greenland Ice Sheet is melting. The actual melting of the ice, most of that takes place at the coast.

Visual: Large chunks of ice floating in the ocean. 

Speaker: Jonathan Overpeck

Yeah, for Greenland, what we're seeing is quite a bit of change and I think a lot of the change is surprising a great number of scientists.

Visual: Map of Earth, with glaciers locations highlighted.

You know, all glaciers around the world are melting, but they don’t hold all that much water.

Visual: A close-up of Greenland, with its borders shrinking, representing glacial melt.

Greenland has about 7 meters of sea level equivalence. So, if that ice sheet melts, all of it, we'll get 7 meters of sea level rise. That's over 20 feet.

Visual: A close-up of Antarctica, with the borders of the West Antarctic Ice Sheet shrinking. 

If the West Antarctic Ice Sheet—the one down in the Southern Hemisphere that we're worried about—melts, that could give us 5 meters of sea level.

Visual: Jonathan Overpeck in office.

So, up to about 40 feet of sea level could result if we melt both of these ice sheets.

Visual: Aerial view of a town on the Greenland coast. Daniel Muhs walks in a quarry, cleared among lush plant life.

It's pretty important to look back at the last time sea level was higher than present day, because you want to figure out, could we in the future go across that threshold?

Speaker: Daniel Muhs, Research Geologist, U.S. Geological Survey

Visual: Daniel Muhs stands by a rock wall in the quarry.

We’re standing here in one of my favorite places in the world, which is Windley Key Quarry, Florida, in the Florida Keys.  And if we had been here 125,000 years or so ago, we’d be underwater by several meters.

Visual: Daniel Muhs gestures toward the quarry walls.  A close-up of the structures in the walls.

What you see here in the quarry walls on either side of us here is a rock called the Key Largo formation. 

Visual: The coral-like structures in the rock face.

It’s a limestone, and about 30 percent of it is composed of corals that were once part of a living coral reef that formed about 125,000 years or so ago during a period we call the last interglacial.

Visual: Daniel Muhs points out brain coral in the rock.

This is a remarkable example of a brain coral in its original growth position. Diploria, or brain corals, are one the most common constituents in the modern reef off Florida today, and here in the Key Largo limestone.

Visual: Daniel Muhs continues to point out features in the rock.

The top of the coral head is here, and you can trace this along the sides, down here to the base of the coral. The top of the quarry here, and very close to the top of this brain coral, are about 5 meters above sea level. And brain corals need to grow in water at least 3 meters deep or so. So that means that sea level has to have been probably anywhere from 6 to 8 meters higher than present during the last interglacial period.

Visual: Close-ups of various coral structures in the rock.

One of the most powerful things about the geologic record of sea level change is it does answer the question, is such a thing possible?

Visual: The rock wall of the quarry.

We know it’s possible because it’s happened in the past.

Visual: Waves crash on a rocky shore.  A sailboat drifts on a body of water in front of a wooded mountain.

Speaker: Jonathan Overpeck

Visual: Buildings at the shore of a waterfront.

Well, it’s not hard to take what we know about the height of coastlines, to get maps showing, as sea level rises, which areas will get flooded, where.

Visual: Jonathan Overpeck at computer

Here’s a visualization showing the Earth and the areas in red that would be submerged with 6 meters of sea level rise.

Visual: Map images of England and Florida.  Shaded red areas indicate varying levels of sea level rise. Map images of New York City and India with shaded red areas indicating sea level rise.

So 6 meters of sea level doesn’t sound like very much, but it’ll affect a very large part of the world’s population and landmass.

Visual: A satellite image of Florida

When we zoom in to finer special scales, it allows us to put a more human face on the sea level rise that could occur in the future.

Visual: A close-up satellite image of a beachfront community in Florida.  Individual buildings are visible.

We can actually see individual communities that will be submerged by sea level rise.

Visual: A zoomed out map of Florida, the Caribbean, the United States, then Earth, with red areas indicating sea level rise.

Science is never certain. What science is all about is trying to figure out what’s probable, what’s not probable, and to be really open with what the uncertainties are.

Visual: A lake

In this case, we know the sea level was higher in the past.

Visual: Daniel Muhs walks in the quarry. 

And we know that was because the Earth was warmer, particularly in the Northern Hemisphere over the Greenland Ice Sheet.

Visual: Daniel Muhs examines a rock wall in the quarry closely with a lens.

The big question is, how much warmer was it?

Visual: Jonathan Overpeck in office.

And both our climate modeling and our paleoclimatic reconstructions suggest that somewhere between three and five degrees Celsius is the temperature by which a lot of Greenland will be melting fast.

Visual: A glacier in Greenland

But to put a little perspective, three to five degrees, how long will it take us to get there?

Visual: A river of meltwater by a glacier’s edge. A traffic jam in the United States.  Smokestacks pump out smoke.

Just in the last 50 years, we've warmed up the Arctic by over two degrees.

Visual: Ice chunks float in the ocean.

So, we're more than halfway to three to five degrees.

Visual: An industrial tower against the sky. Electrical towers tangle a grassy hill.

And sometime later in this century we'll cross that mark.

Visual: A crowded city sidewalk. The 109th Airlift Wing exits its transport plane, landed on the ice.

In our work we don’t know for sure where the threshold is beyond which the ice melting is inevitable.

Visual: A glacier face bordered by meltwater. 

But we know it’s coming.

Visual: A person and dog walk along a shoreline.  A man with waders fishes among crashing waves in the ocean.  A traffic jam.  A mother and child on the beach. 

And if we don’t do something about greenhouse gas emissions soon, we’re going to cross that threshold, and future generations are going to
have to deal with that big sea level rise.

Video ends here.