Trillion-tonne iceberg finally snaps off West Antarctic ice shelf, scientists confirm.

A TRILLION-ton iceberg which has broken free from Antarctica will do nothing to raise the world’s sea levels. But it has changed the face of the southern continent forever.

“The iceberg weighs more than a trillion tonnes, but it was already floating before it calved away so has no immediate impact on sea level,” a Swansea University research team said. It will likely be named A68.

The massive ice cube is twice the size of the Australian Capital Territory, four times the size of London and twice the size of Luxembourg. It is about 350 metres thick.

The iceberg is more than one and a half times the size of Adelaide (3258 square kilometres), a third of the size of Brisbane (15,826 square kilometres) and more than half the size of Melbourne (9990 square kilometres).

The 5800 sq km block of ice is not the largest to have ‘calved’ from Antarctica: an 11,000sq km ‘berg’ was seen to break loose from the Ross Ice Shelf in 2000.

The new berg itself is destined to crumble into the sea, scientists say, fragmenting as it drifts north into warmer waters.

And these colossal icebergs don’t melt fast. Large chunks of the Ross Ice Shelf berg, named B15, were still bobbing about the Southern Ocean two years later.

But the freshwater iceberg is expected to contribute only about 0.1mm to sea levels as it is already floating, says climate scientist Gavin Schmidt. If it had slipped into the sea from the land, the added volume would have been much greater — 2.8mm.

This does not reduce the significance of the breakaway, which happened at some point between Monday and Wednesday.

“This puts the ice shelf in a very vulnerable position,” said Martin O’Leary, a member of the Swansea University monitoring team that first announced the iceberg’s formation on Wednesday. “This is the furthest back that the ice front has been in recorded history. We’re going to be watching very carefully for signs that the rest of the shelf is becoming unstable.”

This is the third ice shelf on the western peninsula of Antarctica to undergo massive ice loss in the past two decades. The Larsen A ice shelf fragmented in 1995. In 2002, Antarctica lost 3250 sq km) of ice when the Larsen B shelf collapsed.

PATTERN OF COLLAPSE

Assistant Professor Duanne White from the Institute for Applied Ecology at the University of Canberra says the past few decades have seen the collapse of over a dozen ice shelves on the Antarctic Peninsula.

“Most of these ice shelves, including Larsen C, are now more retreated than at any time since global climate stabilised at the start of the Holocene, (about) 10,000 years ago,” she says.

The glaciers sitting behind Larsen C hold relatively little ice in the context of the whole of Antarctica.

“However, should this be the start of the breakup of Larsen C, it adds weight to the question of the stability of the larger, more southerly ice shelves and ice drainage systems, which have the potential to contribute several metres to sea level rise during the next few centuries,” she says.

It is as yet uncertain what the giant iceberg represents.

The ice shelf could regrow, replenished by glaciers steadily feeding it from higher terrain.

Or, like the once nearby Larsen B shelf, it could become less stable and completely collapse.

Swansea University researcher Adrian Luckman says opinions are divided.

“Our models say it will be less stable, but any future collapse remains years or decades away,” he says.