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Antarctic Glaciers -

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Antarctic Glaciers (29/04/2010)

TRANSCRIPT

NARRATION

The seas are rising. How fast and how high they will go is the big unknown. But one thing is
certain. What happens in Antarctica will be critical. Around 90 percent of the planet's snow and
ice is found here. Is the sleeping giant stirring?

Dr Tas Van Ommen

We're actually seeing a picture of a much more dynamic continent than we might have thought ten or
fifteen years ago.

Dr James Hansen

Both of the ice sheets have begun to lose mass more and more rapidly.

Neal Young

Here is actually happening, and it's happening now.

NARRATION

What's happening to the world's biggest ice sheet and how will it affect sea level rise? To find
out, we're heading to the opposite ends of the highest, driest and coldest continent on Earth.

Dr Paul Willis

I'm cruising to the Antarctic Peninsula.

Mark Horstman

And I'm travelling to East Antarctica.

NARRATION

To understand ice sheet behaviour in Antarctica, you need to appreciate the divide between east and
west. The transantarctic mountain range effectively splits the massive ice sheet in two.

Dr Ian Allison

Snowfall accumulates in the interior and that is balanced by the drainage of the ice by glaciers,
which are basically like rivers.

NARRATION

Many glaciers end in large floating ice shelves, which gradually break off in the form of icebergs.
If more ice discharges at the ocean than snow falls in the interior, Antarctica begins to lose
mass. The greatest changes are being seen in the west, in particular the mountainous peninsula
which stretches toward South America.

Dr Paul Willis

The Antarctic Peninsula is warming at an astounding rate. For each decade for the last fifty years,
air surface temperatures here have gone up half a degree Celsius. And large chunks of this region
are simply breaking up and floating away.

Neal Young

Some ice shelves have disappeared, Others have broken up catastrophically over a short period of
time.

NARRATION

The Larsen B ice shelf collapsed in 2002. It took just five weeks for more than three thousand
square kilometres of ice, to completely disintegrate.

Neal Young

And it said something to us that things can happen quite quickly. It was thinning for a long period
of time. Fractures were developing in the ice shelf and the atmospheric temperatures were warming.
In that part of the peninsular in the summer time the surface snow gets to melting point, you can
have pools, almost small lakes forming on the surface of the, the ice shelf. And it can force its
way down through the snow and open up a fracture. That contributes to the break up of the ice
shelf.

NARRATION

The Wilkins Ice shelf is the latest of seven ice shelves on the Peninsula to start collapsing, and
it's the furthest south. Ice shelves are already floating, so they can't contribute to sea level
rise. It's what's behind them that's the big concern. But now it is all too familiar. Seven shelves
on the Antarctic peninsula have collapsed in the past two decades. This is a region of the huge
Wilkins ice shelf which collapsed in 2008.

Dr Ian Allison

If you take that barrier away, the big glaciers behind it will flow more quickly.

NARRATION

Glaciers that drained into the Larsen B ice shelf have sped up by a factor of seven.

Neal Young

That does contribute to sea level rise. The quantity of ice in the Antarctic Peninsula region
though is small. The key message is what would happen in the east and to the major glaciers in the
West Antarctic if such changes were to occur there? That would be a consistent, persistent and very
ominous I think change in the scenario.

NARRATION

And there's strong evidence that change is already occurring. In the Amundsen Sea region,
glaciologists have found the major glaciers are speeding up and losing mass, thinning by up to nine
metres a year. What's remarkable is the thinning extends hundreds of kilometres into the grounded
ice sheet.

Neal Young

The major effect is probably a change in ocean circulation bringing in water that is warming that
heat melts the ice and thins it.

NARRATION

The big concern about the West Antarctic ice sheet is that it sits on bedrock that is mostly well
below sea level. This makes the whole ice sheet vulnerable to the encroachment of seawater.

Neal Young

And that could lead to perhaps a runaway effect, that thinning leads to greater speed, leads to
greater discharge, leads to greater thinning.

Dr Paul Willis

The Antarctic Peninsula and the Amundsen Sea regions in West Antarctica are areas of rapid change.
But the Antartic ice sheet is so massive it doesn't behave in a uniform way. In fact in the east,
it's a different story.

Mark Horstman

It's the middle of summer here in East Antarctica, and right now the air temperature is minus four
degrees and dropping. There's no way that air temperatures like this are going to melt any ice. And
In fact, until just recently, it was thought that the ice sheet on this side of the continent was
actually growing in size.

NARRATION

But alarming new evidence indicates this trend has reversed.

Dr James Hansen

We began in 2002 to make very precise measurements of the mass of these ice sheets with the gravity
satellites called GRACE. It consists of two satellites that are following each other.

NARRATION

The distance between the two satellites changes according to the gravitational pull of the mass
below. The data is telling us East Antarctica has been losing mass since 2006. Around 60 billion
tonnes a year. The uncertainty of gravity measurements can be fairly large, but Neal Young says the
results are backed by his research, that uses a different satellite system.

Neal Young

I've been working with a system called ICEsat that has a laser altimeter on it and measures the
surface elevation of the ice sheet and I've been able to see that over the grounded part of the
Totten Glacier the surface has gone down by as much as ten metres over sixteen years. That change
in surface elevation is ongoing and in fact it is increasing in rate. So it is accelerating. Well,
the only way we can get surface lowering like this is for the ice sheet to thin. If it's thinning
it's losing mass, I believe, and others believe the trigger is what's happening in the ocean. We've
not seen this rate of surface lowering anywhere in East Antarctica before.

Mark Horstman

The results are surprising because the ice sheet on this side of the continent is higher, thicker
and colder than the ice sheet in the west. It's thought to be a lot more stable. But there's a lot
we don't know about what lies beneath.

Dr Tas Van Ommen

While we thought East Antarctica was an ice sheet sitting largely on elevated bedrock, we now know
that there are really large regions of East Antarctica that are based on very deep basins which are
below sea level.

Mark Horstman

Airborne technology is providing critical data on the bedrock and other features which may affect
ice flow.

Dr Tas Van Ommen

The aircraft is equipped with gravity sensors, laser altimeters and radar and that allows it to
actually get a reflection off the bedrock underneath the ice sheet at the same time as its
measuring the height of the surface of the ice sheet. So that gives you the thickness.

NARRATION

The discovery of vast lakes beneath the glaciers means sections of the ice sheet may be lubricated
at the base and able to travel faster than regions frozen to the bedrock.

Dr Tas Van Ommen

The way this all interacts is an integral part if you like of modelling the response of the ice
sheet to climate change in the future.

Neal Young

Certainly what's coming out now is a very strong and clear picture that big things can happen in
the ice sheets. It could have a dramatic effect on the ultimate sea level rise over this coming
century.

Dr Ian Allison

I've seen reports that it may increase up to three metres, five metres even by the end of the
century personally I don't think that's possible. But it's not going to more than about one, one
and a half metres in the century which is still a very real concern.

NARRATION

So why do we keep hearing reports that Antarctica is growing? The sea ice that floats around the
continent has increased to a small degree due to changes in polar winds but that doesn't affect sea
levels. What matters is the grounded ice sheet.

Dr James Hansen

Antarctica was losing mass at about 75 cubic kilometres per year, well that's now doubled to about
150 cubic kilometres a year. So that's beginning to worry glaciologists.

Mark Horstman

What we've revealed here is a complex story about Antarctica under changing climates. And the take
home message, like the continent itself, comes in two parts. Here in the East, it appears that it's
a warming ocean thats driving the changes in the ice sheet.

Dr Paul Willis

Whereas here in the West the ice is melting from above and below. When it comes to sea level rise,
Antarctica the sleeping giant is waking up.