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.
