In December last year, a long-running rift in northern Antarctica suddenly went into overdrive. In just a couple weeks, the crack on the Larsen C ice shelf increased by 18 kilometres.
When it takes off, glaciologists predict the iceberg area to be roughly 5000 square kilometres, which is almost twice the size of Australian Capital Territory.
There’s plenty of confusion about the impact such an event may have, so we spoke to polar geodesy professor Matt King from the University of Tasmania to clear some things up.
Is this a freak event?
Not really - but it is a bigger-than-usual iceberg.
“The normal life cycle of a snowflake that falls on Antarctica is to slowly get compressed into ice, to flow down off the land into the ocean, where it eventually either melts or turns into an iceberg,” explains King.
“This is the way Antarctica works, there's nothing particularly unusual about an iceberg calving; icebergs are just a normal, healthy part of an ice sheet.”
Bigger icebergs such as this one about to break away from Larsen C are less frequent, but that doesn’t necessarily mean it is “particularly unusual.” However, scientists do say that, in terms of size, this one will be in the top 10 of icebergs we have records of.
Is this bad news?
It could be—but we don’t yet know what’s going to happen. An iceberg can calve off and have no impact on the sea level, but it can have a larger impact if it leaves the rest of the ice shelf vulnerable.
Since ice shelves are floating extensions of land-based glaciers that flow into the ocean, they prevent the rest of the ice from flowing down to the coast at great speeds, which would definitely contribute to sea-level rise.
Glaciologists, including researchers from the British Antarctic Survey, have been monitoring Larsen C for years. Its neighbours, Larsen A and Larsen B, collapsed in 1995 and 2002 respectively.
If this huge iceberg leaves Larsen C vulnerable to a complete collapse, this might indeed be significant, says King.
“It's not yet clear if that might be the case, but computer modelling suggested it might be,” he explains. “If the iceberg does calve off and leave it in that situation, there's going to be a lot more things going on in the next years, decades—it's hard to know how long that could take.”
The rift on Larsen C, observed by NASA IceBridge mission on 10 November 2016.
PHOTOGRAPH BY NASA/John SONNTAG
Did global warming do this?
There’s no direct evidence, but scientists are actively working on figuring that out.
“We know that the atmosphere in this area has warmed incredibly quickly,” says King.
The Antarctic Peninsula is one of the fastest-warming regions on our planet—over the last half of the last century it experienced a temperature rise of 2.5°C. Whether it’s the cause of recent ice shelf collapses is yet to be determined.
However, Larsen C, which averages a thickness of 350 metres, has likely been there for thousands of years, since the last interglacial period.
“We think that this ice shelf has been around for at least 120 thousand years, so if it did collapse, that would be a big deal,” King explains.
What’s going to happen next?
According to expert predictions, in the next few months we can expect the last 20 kilometres of the rift to crack, and the iceberg will take off.
Preliminary computer modelling shows this might spell doom for Larsen C as a whole, although it’s too soon to tell—and Professor King emphasises we may not know the whole situation for years to come.
“That’s why, when the iceberg breaks off, scientists will be monitoring the speed of the ice that remains, the thickness of the ice, they'll be trying to understand whether there's actually any change of behaviour [of the glacier].”
One thing is clear—keeping a close eye on Antarctic calving is crucial if we want to accurately predict sea-level rises into this century.
Header image: NASA photo of the Larsen C rift, taken on 10 November 2016.