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Icebergs breaking off Antarctica, even massive ones, do not typically concern glaciologists. But the impending birth of a new massive iceberg could be more than business as usual for the frozen continent.

The Larsen C ice shelf, the fourth-largest in Antarctica, has attracted worldwide attention in the lead-up to calving an iceberg one-tenth of its area – or about half the area of greater Melbourne. It is still difficult to predict exactly when it will break free.

But it’s not the size of the iceberg that should be getting attention. Icebergs calve all the time, including the occasional very large one, with nothing to worry about. Icebergs have only a tiny direct effect on sea level.

The calving itself will simply be the birth of another big iceberg. But there is valid concern among scientists that the entire Larsen C ice shelf could become unstable, and eventually break up entirely, with knock-on effects that could take decades to play out.

Ice shelves essentially act as corks in a bottle. Glaciers flow from land towards the sea, and their ice is eventually absorbed into the ice shelf. Removal of the ice shelf causes glaciers to flow faster, increasing the rate at which ice moves from the land into the sea. This has a much larger effect on sea level than iceberg calving does.

While the prediction that Larsen C could become unstable is based partly on physics, it is also based on observations. Using aerial and satellite images, scientists have been able to track very similar ice shelves in the past, some of which have been seen to retreat and collapse.

The death of an ice shelf

The most dramatic ice shelf collapse observed so far is that of Larsen C’s neighbour to the north – the imaginatively named Larsen B. Over the course of just six weeks in 2002 the entire ice shelf splintered into dozens of icebergs. Almost immediately afterwards, the glaciers feeding into it sped up by two to six times. Those glaciers continue to flow faster to this day.

Satellite photo series of Larsen B Ice Shelf collapse from January 2002 to April 2002. NASA

In our new study, published in Earth and Planetary Science Letters, we turn the clock back even further to look at the Wordie ice shelf, on the west coast of the southern Antarctic Peninsula, which began to retreat in the 1960s and eventually disappeared in January 2017.

Over the past 20 years, observations have shown that the main glacier feeding into the Wordie ice shelf, the Fleming Glacier, has sped up and thinned. Compared with the glaciers feeding Larsen B and C, Fleming Glacier is massive: 80km long, 12km wide, and 600m thick at its front.

Locations of the Larsen C Ice Shelf and the Wordie Ice Shelf-Fleming Glacier system with ice front positions from 1947 to 2016. Author provided

We used historic aerial photographs from 1966 to create an elevation map of the Fleming Glacier, and compared it to elevation measurements from 2002 to 2015. Between 1966 and 2015 the Fleming Glacier thinned by at least 100m near the front. The thinning rate, which is the elevation change rate, rapidly increased: the thinning rate after 2008 is more than twice that during 2002 to 2008, and four times the average rates from 1966 to 2008.

Ice thinning rate of the Fleming Glacier region during (a) 2002-2008 and (b) 2008-2015. Author provided

Ice flow speeds have also increased by more than 400m per year at the front since 2008. This is the largest speed change in recent years of any glacier in Antarctica. These changes all point to ice shelf collapse as the cause.

We estimate the total glacier ice volume lost from all glaciers that feed the Wordie is 179 cubic kilometres since 1966, or 319 times the volume of Sydney Harbour. The weight of this ice moving off the land and into the ocean has caused the bedrock beneath the glaciers to lift by more than 50mm.

Other research has suggested this lift could have acted to slow the glacier’s retreat, but it’s clear that the bedrock deformation has not stopped the ice movement speeding up. It seems the Fleming Glacier has a long way to go before it will return to a new stable state (in which snowfall feeding the glacier equals the ice flowing into the oceans).

Fifty years after the Wordie Ice Shelf began to collapse, the major feeding glaciers continue to thin and flow faster than before.

We can’t yet predict the full consequences of the new iceberg calving from Larsen C. But if the ice shelf does begin to retreat or collapse, history tells us it is very possible that its glaciers will flow faster – making yet more sea level rise inevitable.

Chen Zhao is a PhD student from the School of Land and Food, University of Tasmania. She receives funding from the Australian Government Research Training Program.

Christopher Watson receives funding from the Australian Research Council and the Department of Environment.

Matt King receives funding from the Australian Research Council and the Department of Environment.

The case was brought over cutting levels of nitrogen dioxide.

Chinese president Xi Jinping officially presents two giant pandas to Berlin’s zoo on Wednesday. German chancellor Angela Merkel said the bamboo-munching newcomers would be special ambassadors for the two countries. The pandas, Meng Meng and Jiao Qing, landed in Berlin on June 24 and have been settling in at the zoo since then, out of public view.

• Panda fever grips Berlin on Chinese president’s trip to Germany
  

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Mike Ashley’s ‘worth’ | American signal crayfish | String theory | Bacon sandwiches | Undergarments | Corbyn on violin

The word “earn” has become meaningless in today’s society, the word “get” being far more appropriate. In the same spirit, please could I urge you to refrain from repeating the misleading use of “worth” when referring to individuals and their personal wealth (Front page, 4 July). Mike Ashley is apparently “worth” £2.2bn – not to me he’s not.
Deirdre Burrell
Mortimer, Berkshire

• Carey Davies’s Country Diary (3 July) about the American signal crayfish in our rivers was interesting, but omitted to include one way of reducing their population: eating them. Fortunately George Monbiot has already provided information on how to do this (Monbiot cooks up revenge on invasive signal crayfish, 30 September 2009). Just make sure it’s not our (now very rare) native species.
Copland Smith
Manchester

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Oliver Yates says any taxpayer money facilitating the proposed Carmichael coalmine carry reputational risks for the government

Any loan the Northern Australia Infrastructure Facility (Naif) gives to Adani’s Carmichael coalmine project would likely be unlawful, according to the former head of the Clean Energy Finance Corporation (CEFC), which operated under an almost identical mandate.

Naif, which was set up to give $5bn of concessional loans to support the development of northern Australia, operates under an investment mandate that includes a clause saying it “must not act in a way that is likely to cause damage to the commonwealth government’s reputation, or that of a relevant state or territory government”.

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Planet could heat up far more than hoped as new work shows temperature rises measured over recent decades don’t fully reflect global warming already in the pipeline

Hopes that the world’s huge carbon emissions might not drive temperatures up to dangerous levels have been dashed by new research.

The work shows that temperature rises measured over recent decades do not fully reflect the global warming already in the pipeline and that the ultimate heating of the planet could be even worse than feared.

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Parliamentary triangle is ideal for bees because Canberra’s centre is relatively free from pollution and has a good range of plants

It is a fact that Canberra has its fair share of honey-tongued politicians but parliament is about to produce its very own product.

Three beehives have been installed in the grounds around Australia’s Parliament House in Canberra to produce honey for sale in the shop and to give as gifts for visiting dignitaries.

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How urban gardens are connecting with nature to bring wildlife into the city.

High court instructs ministers to publish full proposals by the end of July

The government has won the latest court challenge over the UK’s air pollution crisis.

Environmental lawyers ClientEarth had argued that ministers’ draft proposals to improve air quality – which contributes to tens of thousands of deaths each year – were unlawful.

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It’s unscientific, fails basic risk management, is bad for the economy, and immoral

Two weeks ago, Senator Al Franken (D-MN) had an exchange with Trump’s Department of Energy Secretary Rick Perry about climate change.

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A recent incident has got some animal rights groups fired up about this issue.

Investigation is part of an £8m research project examining impacts on land, water and air of the extraction technique

Scientists will investigate how fracking can affect drinking water and its role in earthquake tremors of the kind caused by shale gas operations near Blackpool, as part of a taxpayer-funded £8m research project.

The programme, backed by the Natural Environment Research Council and Economic and Social Research Council, will examine hydraulic fracturing’s environmental impacts on land, water and air, as well as public attitudes to the controversial extraction technique.

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Subverting superhighways with sorry quietways; preserving motor vehicle capacity even if it brings conflict with cyclists – the mayor must do better

Do you remember that Blackadder scene where General Melchett proudly unveils a map representing the territory gained by his troops? Dimensions: 17 sq ft. Scale: actual size. London mayor Sadiq Khan’s cycling programme – formerly Britain’s bike flagship – is starting to feel a bit like that.

More than a year since he took office pledging to “make London a byword for cycling”, “accelerate” the existing programme and “triple” to 36 miles the length of segregated cycle superhighways, the mayor has by my count opened 80m (260 ft) of new segregated lane. Work is progressing, extremely slowly, on another half-mile or so. And that is about it.

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Powis Castle, Wales A dangerous beauty stolen by European adventurers and hinting of vast plains a world way

The anchor plant, Colletia paradoxa, with its geometric architecture, looks like trouble among the summer flowers in the herbaceous borders on the terrace gardens. And yet its very oddness makes it fit with an assembly of plants few, if any, of which would grow together in the wild. A paradox indeed.

Plants from the Americas, the far east and Europe grow cheek by jowl according to an aesthetic based on colour and form rather than geography. Although many do share similar ecological characteristics, some appear suited for other planets.

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Works begin on Ratch Australia's 42.5MW solar farm, which is being constructed on the site of a former coal power plant.

Things are becoming predictable in the Victorian Energy Efficiency Certificate market, even if that is supply side’s ability to surprise. Meanwhile, in NSW, a stunning development.

Last week's speech by NSW energy minister Don Harwin was exactly the sort of thing Malcolm Turnbull used to say about climate and energy policies, before he became master of all he surveyed – apart from his own climate and energy policies.

“the Code for Smart Communities will set new benchmarks for smart cities and communities across Australia, New Zealand and beyond, by providing important guidance on how to use technology, data and intelligent design to accelerate more efficient, liveable and sustainable development projects"

With renewable investment accelerating way faster than most anticipated a year ago, it's likely parts of the transmission grid will become constrained. We need action, not more analysis.

Farmers are using far greater amounts of untreated waste water on crops, posing risks to public health.