JUDY WOODRUFF: But first: Researchers have been watching for months, waiting for a huge
iceberg to break away from an ice shelf in Antarctica.
That break was confirmed today.
And just to give you a sense of the size, the volume of the iceberg is said to be twice
as large as Lake Erie.
Miles O'Brien has been watching all this and digging into the larger questions about the
ice shelf.
Here's an update to an earlier report.
It's part of our weekly segment on the Leading Edge of science.
MILES O'BRIEN: This fast-growing rift in the Antarctica ice just created one of the largest
icebergs ever recorded, about the size of Delaware, weighing more than one trillion
tons.
The event had been anticipated for months.
Finally, some time between Monday and today, the Larsen Sea Ice Shelf became 12 percent
smaller.
So, we have known about this for quite a while, right?
KELLY BRUNT, University of Maryland: We have certainly known about the bulk of this rift
for a while.
MILES O'BRIEN: Kelly Brunt is a glaciologist at the University of Maryland and NASA's Goddard
Space Flight Center.
She used a wall of monitors there to show me the growing rift, fueled in part by rising
air and sea temperatures.
If the glaciers in West Antarctica all dropped into the water, global sea level would rise
by more than 15 feet.
Brunt showed me the big picture, a composite of images from several satellites.
This is how the glacier ice flows here.
KELLY BRUNT: Ice flows from the center of the continent out to the edges, much like
syrup on the center of your pancake flowing towards the edges.
And you can see there are areas where it's moving pretty slowly, and then there are areas
where it's moving very quickly.
And those quick places are generally in our areas of ice shelves.
MILES O'BRIEN: So, when we think about ice, we think about something static.
It's not static, is it?
KELLY BRUNT: Not at all.
Actually, it's highly dynamic.
You can see from this image it looks to me a lot like a river system.
MILES O'BRIEN: Ice shelves are connected to the glaciers that sit on land, but they are
also floating, like ice cubes in a glass of water.
KELLY BRUNT: If you had a drink with ice cubes in it, as those ice cube melts, they don't
add to the height of the water in the glass.
So when ice shelves break down and collapse, they do not have a direct impact on mean sea
level rise.
However, they have an indirect effect.
These ice shelves buttress the flow of the ice upstream, the ice that's flowing into
the system.
And when you lose that buttressing force, you allow the upstream glaciers to flow faster.
So that's similar to putting more ice cubes into the glass and letting those melt.
MILES O'BRIEN: Ice falls off the edge of glaciers all the time.
It is part of a natural process called calving.
Kelly Brunt says it is important to judge the size of the piece that breaks off relative
to the size of the glacier that is behind it.
She says your fingernails offer a handy model.
KELLY BRUNT: If you break your fingernail inside the white part of your fingernail,
you probably don't think much of it.
If you break it below the white part, you put a Band-Aid on it, you think about it and
you keep an eye on it.
If you lose your whole fingernail, I don't know what happens.
It's pretty catastrophic.
This represents losing the whole fingernail.
MILES O'BRIEN: Like so many features in Antarctica, the Larsen Ice Shelf is named for a famous
19th century explorer.
And it is disappearing, section by section, identified by letters.
Larsen A disintegrated in 1995.
And, in 2002, a series of satellite images captured the end of Larsen B in dramatic fashion
over the course of six weeks.
The piece that broke off was the size of Rhode Island.
KELLY BRUNT: Losing this much ice, losing ice that represents roughly the state of Rhode
Island in a month-and-a-half, just far exceeded anybody's expectations of what could happen
in the time scale that it could happen.
MILES O'BRIEN: So, it was kind of like, we have to rethink things here a little bit.
I mean, this is a wakeup call.
KELLY BRUNT: This was absolutely a wakeup call.
MILES O'BRIEN: Scientists track the ice using a half-dozen U.S. and European satellites,
including Landsat, which gathered these images.
But some of their best data came from a satellite called ICESat.
Launched in 2003, it ceased operation in 2009.
It precisely measured the glaciers using laser beams.
KELLY BRUNT: This is quite a few years of ICESat data merged together to get a sense
in meters per year how our ice sheet is changing.
And you can see, the big picture here is that our ice sheets are changing where they are
in contact with both our warming atmosphere and a warming ocean.
So, it's basically along the fringe of the continent.
MILES O'BRIEN: When ICESat failed, NASA started tracking the ice using radar and lasers on
board low-flying aircraft.
The IceBridge program is NASA's largest air campaign ever, but it still could not match
the eye above the sky.
It goes without saying that you would view these satellites, the capability to look at
this, as essential?
KELLY BRUNT: What we're talking about is a calving of an iceberg that's a size of a state.
To get that, you really need a satellite to be able to see all of it in one shot.
It's a function of scale and repeatability to go back and look at that area again with
the satellite that makes these the perfect tools for looking at the large-scale change
that we're seeing in this region.
MILES O'BRIEN: And that's precisely what Kelly Brunt and her colleagues will be doing now,
using satellite data, data from the scant weather stations that are on the surface there,
and additionally with buoys which are in the water itself.
They will be poring over this data over the course of actually years to try to make some
sort of definitive statement -- and I put definitive in quotes because it's science,
after all -- as to whether this particular calving event is linked to climate change
-- Judy.
JUDY WOODRUFF: So, is there a definitive answer to that at this point?
It sounds like you're saying no.
MILES O'BRIEN: Not just yet.
Here's what we know.
Larsen B, the previous big calving event, scientists say there is a very strong pile
of evidence indicating it is linked to climate change.
Larsen A, they have practically no data at all.
So, it's one of these things that, as Kelly Brunt put it, this is where it gets exciting
for scientists.
They will try to determine if it's climate change that actually caused this to happen,
and also they will be looking at the stability of the ice shelf behind it.
Does the flow increase?
What about the glacier behind the ice shelf itself?
Looking at all that will give them a lot of clues about what this is going to mean ultimately
for sea level rise.
JUDY WOODRUFF: And speaking of that, do they know the effect this is going to have on sea
levels in the area and around the world?
MILES O'BRIEN: Yes, that's the big question.
Larsen C, even though it's called a shelf, it's kind of misleading.
It was already in the water.
And so like an ice cube in a glass of water, it had already done its bit of displacement
and already had made its impact on sea level rise.
If it had fallen off, scientists estimate it would have increased sea level across the
world by three millimeters.
That the gives you the idea of the size of this.
So, now the situation here is to see whether the increased rate, if there's an increased
rate in the flow of that ice shelf into the water, what impact that might have on sea
level rise in coming years.
But, again, Judy, this is long-term science, and we will just have to watch it for years
to come.
JUDY WOODRUFF: So, finally, Miles, what happens to this gigantic piece of ice now that it's
broken off?
MILES O'BRIEN: Well, it will probably not stay intact the size of Delaware.
It will break up over time.
Fortunately, where it is, it's not going to be in the way of any shipping channels.
So it shouldn't be a hazard to navigation, but that's a big part of what is going to
happen along with the other research.
They will be tracking to see how this iceberg breaks up.
But it will be a big iceberg to start, and over time it will get smaller.
JUDY WOODRUFF: All right, our iceberg man, Miles O'Brien, thank you very much.
MILES O'BRIEN: You're welcome, Judy.