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.

Just for fun calc: iceberg will add 0.1mm to sea level as it melts because fresh (no salt). It wld have been 2.8mm if not already floating. pic.twitter.com/eTUTKK9Qdm — Gavin Schmidt (@ClimateOfGavin) July 12, 2017

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.

#Climatechange signal behind #LarsenC break-up best seen in regional progress of ice shelf collapse toward pole https://t.co/P9S8kCEFeD pic.twitter.com/dWUxqxp2jw — Climate Signals (@ClimateSignals) July 12, 2017

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.

Updated #Sentinel1 InSAR sequence shows final branching at the rift tip as it reaches within 4.5 km (2.8 miles) of breaking through to calve pic.twitter.com/6F1Bs8Zmkv — Adrian Luckman (@adrian_luckman) July 6, 2017

The rift which produced the breakaway was first observed in the 1980s, he said, and was already a ‘long established feature’.

“There is no direct evidence to link its recent growth to either atmospheric warming, which is not felt deep enough within the ice shelf, or ocean warming, which is an unlikely source of change given that most of Larsen C has recently been thickening,” he recently wrote.

What is not in dispute is the steady decline of the extent of nearby ice sheets.

ON THE LOOSE

According to recent data from the European Space Agency, the gargantuan berg — at its deepest — extends some 210m beneath the surface.

That’s roughly the equivalent of a 64-storey tall building.

The ESA determined the berg’s size and depth through monitoring satellites: the CryoSat mission and the Copernicus Sentinel-1 radar pair.

Massive 2240 sq mi (5800 sq km) iceberg fractures off Antarctic ice shelf like a cracked eggshell: https://t.co/e02PP9dZJ5 #climate pic.twitter.com/mQMHsmySE0 — NASA Climate (@NASAClimate) July 12, 2017

Overall, it contains 1155 cubic kilometres of solid ice.

And ice floats.

Icebergs calve from Antarctica all the time.

Exactly where it will go is a matter of some anxiety.

According to an ESA press release:

“We are not sure what will happen,” it reads. “It could, in fact, even calve in pieces or break up shortly after. Whole or in pieces, ocean currents could drag it north, even as far as the Falkland Islands. If so it could pose a hazard for ships in Drake Passage.”

So ongoing monitoring of the iceberg’s fate will be essential.

A similar sized berg drifted free around the Antarctic Brunt ice shelf in 2015, causing some concern for the nearby Halley research base.

CLIMATE CHANGE WAKE-UP

Greenspace international science unit chief Paul Johnston said the melting of ice in Antarctica was recognised as a “canary in the coalmine” warning the world of the dangers of climate change.

“The collapse of this ice-shelf, the third collapse in this region in recent years, is possibly yet another signal of the global impact of climate change — and the imperative of implementing the Paris climate agreement, shifting to 100 per cent renewable energy sources and leaving fossil fuels in the ground,” he said.

“No one knows for sure if climate change played a definitive role in the break of the Larsen C ice shelf, but given the relatively recent breakup of other shelves, and the contribution thought to have been made to erosion of the ice by warmer waters around the Antarctic Peninsula in those cases, it seems likely that human activities are a factor.

“We’re still in the safe zone for avoiding catastrophic climate change. But we must act fast. Decisions taken now by governments and industry will decide whether billions of people have safe, prosperous lives in the future.”

ICE SHELVES EXPLAINED

Ice shelves float on the sea, extending from the coast, and are fed by slow-flowing glaciers from the land.

They act as giant brakes, preventing glaciers from flowing directly into the ocean.

If the glaciers held in check by Larsen C spilt into the Antarctic Ocean, it would lift the global water mark by about 10 centimetres (four inches), researchers have said.

The calving of ice shelves occurs naturally, though global warming is believed to have accelerated the process.

Warmer ocean water erodes the underbelly of the ice shelves, while rising air temperatures weaken them from above.

According to an ongoing temperature analysis conducted by scientists at NASA’s Goddard Institute for Space Studies (GISS), the average global temperature on Earth has increased by about 0.8° C since 1880.

Antarctica is one of the world’s fastest-warming regions.