A rift in the Larsen C shelf, pictured on June 1 © AFP

A vast iceberg nearly the size of the US state of Delaware has finally broken away from Antarctica in a move that is likely to alter the frozen landscape forever.

Scientists have been waiting months for the dramatic calving of the iceberg, one of the biggest on record at almost 6,000 square kilometres, after huge cracks emerged on the Larsen C ice shelf in west Antarctica.

That left the one trillion tonne iceberg hanging by a thread of ice just 4.5km wide, according to researchers at Project Midas, a UK-based research project investigating the effects of a warming climate on the Larsen C shelf.

“It’s a massive change,” said Andrew Fleming, a remote sensing analyst from the British Antarctic Survey (BAS) who saw some of the first detailed imagery of the break on Wednesday morning. “This is a fairly big step backwards.”

Because ice shelves are floating extensions of land-based glaciers that flow into the ocean, the splitting off of the gigantic iceberg is not expected to have any immediate effect on sea levels.

However, ships could face extra risks if the iceberg breaks up and parts of it drift into warmer waters.

The iceberg could remain in one piece but is more likely to break into fragments according to Adrian Luckman, a professor at Swansea university and lead investigator of the Midas project.

“Some of the ice may remain in the area for decades, while parts of the iceberg may drift north into warmer waters,” Prof Luckman said.

The greater risk to shipping does not come from large icebergs, which are relatively easy to monitor, but smaller, partly submerged ice. Almost a decade ago about 150 people had to be rescued from the Explorer cruise ship after it struck ice off Antarctica.

Iceberg calvings occur naturally and many scientists say there is no definitive sign that climate change caused the Larsen C berg to break free.

However, ice shelves act as huge buttresses that hold back glaciers flowing down to the coast, so researchers will be watching the Larsen C shelf closely for further signs of deterioration.

When the Larsen A and B ice shelves further north of Larsen C collapsed in 1995 and 2002 respectively, there was a “dramatic acceleration” of the glaciers behind them, said David Vaughan, director of science at the BAS.

This led to larger volumes of ice making its way into the ocean, contributing to sea level rise, Prof Vaughan added. “If Larsen C now starts to retreat significantly and eventually collapses, then we will see another contribution to sea level rise.”

Martin O’Leary, another glaciologist with the Midas project, said his team was not aware of any link between the latest calving and human-induced climate change. However, he said the move puts the front of the ice shelf in a vulnerable position.

“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,” he said.

Scientists at the BAS said there was “little doubt” that climate change was causing ice shelves to disappear in some parts of Antarctica, but no obvious sign that climate warming was causing the whole of Antarctica to break up.

“There are other parts of Antarctica which are losing ice to the oceans but those are affected less by atmospheric warming and more by ocean change,” said Prof Vaughan. “Larsen C itself might be a result of climate change, but in other ice shelves we see cracks forming which we don’t believe have any connection to climate change.

“For instance on the Brunt Ice Shelf [in Antarctica] where BAS has its Halley Station, there those cracks are a very different kind which we don’t believe have any connection to climate change.”

Copyright The Financial Times Limited 2018. All rights reserved.