In a sign of the effect of global warming, scientists believe a massive ice shelf is due to break away from Antarctica's Larsen C ice shelf within the next few months.
A slow-progressing rift suddenly grew by 18 kilometres (11 miles) at the end of December, leaving the finger-shaped chunk – 350 metres thick – connected along only a small fraction of its length. The rift has also widened, from less than 50 metres (160 feet) in 2011 to nearly 500 metres today.
By itself, the soon-to-be iceberg will not add to sea levels, the likely consequence of ice sheet disintegration that most worries scientists. The real danger is from inland glaciers, held in place by the floating, cliff-like ice shelves that straddle land and sea.
The fragile West Antarctic ice sheet – where Larsen C is located – holds enough frozen water to raise global oceans by at least four metres (13 feet).
Dr Amber Leeson gives more details.
The breaking off, or calving, of ice shelves is a natural process, but global warming is thought to have accelerated the process.
Warming ocean water erodes their underbelly, while rising air temperatures weaken them from above.
The nearby Larsen A ice shelf collapsed in 1995, and Larsen B dramatically broke up seven years later.
The ice block currently separating from Larsen C contains about 10 percent of its mass, and would be among the 10 largest break-offs ever recorded, Luckman said.
If all the ice held back by Larsen C entered the sea, it would lift global oceans by about 10 centimetres (four inches).