Petr Hlavacek

The cold, hard truth

The record of the Earth’s past climate has been frozen in ice­ bound up in ice sheets and glaciers on land, and floating on the seas in great ice shelves. Cores extracted from this ice tell an alarming story, and dramatically alter climate projections.

Written by       Photographed by Petr Hlavacek and Andris Apse

Meltwater rages down the Waiho River at the terminal of the 12-kilometre-long Franz Josef Glacier. In 2011, the lower glacier was deemed too unstable for glacier tours on foot and now tourists access the Franz Josef only by helicopter. Later, the foot of the glacier thinned so dramatically—a process glaciologists call down-wasting—that it collapsed, leaving only a frail bridge of ice over the terminal cave. Following the line of the Waiho River into the background, Sentinel Rock can be seen, an outcrop on the valley floor that marked the terminal of the glacier just over 100 years ago.
Meltwater rages down the Waiho River at the terminal of the 12-kilometre-long Franz Josef Glacier. In 2011, the lower glacier was deemed too unstable for glacier tours on foot and now tourists access the Franz Josef only by helicopter. Later, the foot of the glacier thinned so dramatically—a process glaciologists call down-wasting—that it collapsed, leaving only a frail bridge of ice over the terminal cave. Following the line of the Waiho River into the background, Sentinel Rock can be seen, an outcrop on the valley floor that marked the terminal of the glacier just over 100 years ago.
Massive seracs and deep crevasses open on the Davis Snowfield, the birthplace of the Franz Josef Glacier. Snow falling on the Main Divide flows east down the Tasman Glacier, and west down the steeper valley of the Franz Josef.
Massive seracs and deep crevasses open on the Davis Snowfield, the birthplace of the Franz Josef Glacier. Snow falling on the Main Divide flows east down the Tasman Glacier, and west down the steeper valley of the Franz Josef.

The Spikes of Brian Anderson’s crampons bite into the hard glacier ice as he leans forward to get a better view of the receiver’s electronics. A mass of batteries and wires nestle in a heavy plastic case fixed to the centre of a waist-high aluminium tripod. The solar cells and battery appear to be working, but all the lights of the inactive GPS unit are on. Normally, it would be receiving a signal every 30 seconds.

“Not a good sign,” says Anderson.

A colleague will need to be consulted by mobile phone when we reach higher ground. Anderson fingers his beard and makes an unkind remark about kea. He later tells me that the inquisitive birds once stripped monitoring equipment on a weather station in the Ben Ohau Range just before he was due to retrieve it, having left it alone for 18 months.

“Good on the kea, don’t get me wrong. It’s just that they are smarter than I am.”

I turn to take in the view. To either side of us, towering walls of schist rise almost vertically to a sky cloaked in heavy cloud. Directly ahead looms the jumbled, broken rise of the Franz Josef Glacier, its névé unseen beyond, amid the peaks of the Southern Alps. In the centre of the ice wall, protruding like a massive coalface in a frozen cataract, is the ‘black hole’—an exposed mass of rock perhaps 100 metres high. Twice, or may be three times, during our stay, a large block of ice breaks from the rim and, with a muffled boom, falls and fragments.

Dwarfed by the vastness of the landscape, a string of visitors and their guide pick their way delicately across the dirty ice, stopping now and then to study an eroded water channel or a beguiling, blue-veined crevasse. The air is alive with the purposeful beat of helicopters at one point I count four—ferrying fresh parties in.

Brian Anderson perches on a ledge high above the Fox Glacier to reposition a solar panel that powers a monitoring camera. The camera takes a picture every hour, recording the flow of the glacier, and events such as crevasse formation and ice collapses as the ice moves down the valley. The Fox Glacier has been rapidly shrinking over the past century and a half, just like the Franz Josef where records of the terminal position date back to 1860. They show a long retreat, marked with a number of small advances due to periodic high snowfall on the Main Divide.
Brian Anderson perches on a ledge high above the Fox Glacier to reposition a solar panel that powers a monitoring camera. The camera takes a picture every hour, recording the flow of the glacier, and events such as crevasse formation and ice collapses as the ice moves down the valley. The Fox Glacier has been rapidly shrinking over the past century and a half, just like the Franz Josef where records of the terminal position date back to 1860. They show a long retreat, marked with a number of small advances due to periodic high snowfall on the Main Divide.

That’s how we arrived—on a four-minute flight from the heliport at Franz Josef township, up a valley whose floor for much of the way is now rock and river-threaded shingle, laid bare by the retreating ice. A collapse of the ice face at the glacier’s terminus has, since March 2012, made walking in too dangerous, though we carry hard hats in case deteriorating conditions ground the chop­pers tomorrow, when we are due to leave.

The well-known art critic and arbiter of late-Victorian taste, John Ruskin, once quipped that the planet’s glaciers were retreating on account of the vulgarity of tourists. Anderson has devoted much of his professional life to deepening an alter­native understanding of the glaciers’ behaviour, through mathematical modelling. A senior research fellow at Victoria University’s Antarctic Research Centre, he divides his time between a desk in Wellington and fieldwork out of his Hokitika home base.

Since first visiting the Franz Josef on a university field trip in 1996, Anderson has regularly crunched over it with a GPS device to map the terrain, and for the past 10 years has tracked its movement the time-honoured way—by noting the position of stakes that every few months he has driven in to the ice. In this way, the effect of snowfall or melt events on glacier dynamics can be measured.

Now, automated cameras and satellite imaging (when budget and cloud cover permit) make things easier. This is the first time in six months that Anderson has set foot here, though even after such a brief absence, the change in ice volume is evident. He raises a hand to Cape Defiance, pointing out the mark, hundreds of metres above the present ice surface, reached by the glacier in 1893 when Charlie Douglas and Arthur Harper recorded its thickness with an aneroid barometer. Since then, the ice tongue has been in gradual retreat, punctuated, as has its neighbour the Fox, by several smaller advances, most recently between 1983 and 2008. Now, the ice is once more withdrawing towards the his­toric minimum it reached in 1980, some three kilometres further back from the sea than it had been less than a century earlier. Anderson’s data shows that in 2011 alone, its surface elevation dropped an astonish­ing 70 metres.

“The computer modelling gets quite scary,” he says.

“Given a scenario of mod­erate 2°C warming and conditions that are 10 per cent wetter, the whole tongue is gone by 2100. With 2.8°C, it starts to break up high in the Chamberlin Snowfield. At that point you might still call the Franz Josef a glacier, but it would be unrecognisable.”

Under those conditions the Almer Glacier, which overhangs the Franz Josef, would be pretty much gone. The Fox fares a little better because it originates on the slopes of Mt Tasman, so is higher and more resilient. The fate of the massive 600-metre­thick Tasman Glacier, on the eastern slopes of the Southern Alps, is harder to predict. Covered in insulating debris and terminat­ing in a lake, it’s subject to entirely different processes. It will undoubtedly endure longer than the others but, ultimately, it too will succumb to the heat. For the glaciers to avoid such a fate, the climate needs to become 50 per cent wetter for every degree of warming—and that’s never going to happen. Indeed, if the scientific modelling is to be believed, not only the icescape of the Southern Alps but the entire cryosphere of the Earth will be transformed.

High on the shoulder of what suddenly seems a disturbingly ice-free Cape Defiance sits our destination for the night, a tiny red-roofed hut used by tahr hunters and alpinists. We reach it, shortly before sundown, after a near-vertical two-hour climb up 600 metres of loose rubble and rock. One of Anderson’s cameras is fixed in a housing at the extreme edge of the ridge. (He has others keeping watch over the Tasman and Fox glaciers.) For some time, it has not transmitted its accumulat­ing gigabytes of stored images, so early the next morning he checks it out, discovering yet more damage wrought by his wilful adversaries. It’s a spectacular spot for outdoor work. In one direction stand the majestic alps; in the other, far off on the coastal plain, the settlement of Franz Josef. And beyond that the distinctive arc of the Waiho Loop, a forest-covered terminal moraine that marks the full reach of Franz Josef Glacier 12,000 years ago. This is, I learn, one of the most finely calibrated places on Earth for studying the effects of climate change and improving our under­standing of how ice ages work.

New Zealand is one of the few land­masses in the Southern Ocean, and its warm, wet maritime climate results in a huge amount of snow accumulating on the névé of glaciers such as the Franz Josef, and an equally prodigious volume of melt at their termini. Unlike glaciers in the Arctic, which get little of either, our maritime gla­ciers are therefore highly sensitive to the subtlest of climatic effects.

Glaciers are shot through with holes—fine capillaries where melt-water seeps, and broad tunnels where it rushes. Often, wind and rainwater also contribute to the erosion, scalloping the walls and polishing the surfaces until it feels like the corridors of a glass cathedral. But this is a structure on the move; the glacier doesn’t only slide but also tumbles—the vertical axis through this tunnel, marked with gravel and dust from rockfalls, was once horizontal.
Glaciers are shot through with holes—fine capillaries where melt-water seeps, and broad tunnels where it rushes. Often, wind and rainwater also contribute to the erosion, scalloping the walls and polishing the surfaces until it feels like the corridors of a glass cathedral. But this is a structure on the move; the glacier doesn’t only slide but also tumbles—the vertical axis through this tunnel, marked with gravel and dust from rockfalls, was once horizontal.

Their recent advance, for example, came at a time of cooler temperatures in this part of the world caused by the El Niño Southern Oscillation, and by volcanic emissions and Pacific trade winds that climatologists say drove heat into the ocean.

Meanwhile, between 2000 and 2010, mountain glaciers in most other parts of the world retreated. It was, says Associate Professor Andrew Mackintosh of Victoria University’s School of Geography, Environment and Earth Sciences, the largest ice loss in Earth’s mountain cryo­sphere in 100 years.

New Zealand’s glaciers are significant not because of their size but their dyna­mism, says Mackintosh, who heads the glacier research group in the university’s Antarctic Research Centre. Most mountain glaciers take decades or longer to respond to sustained climate signals, expressing year-to-year climate change in terms of their mass balance—the difference between snowfall and ice melt, averaged over the whole glacier. But it takes time for any mass gain to be transmitted through the glacier and manifest itself as a change in the position or wall-height of its termi­nus. Thanks to their steepness, the amount of snow deposited in their catchments, the funnel-shaped topography and their fast melt, our glaciers register change faster than others anywhere else on Earth.

Over the course of last century, three kilometres of the Franz Josef Glacier simply disappeared. By 2100, say glaciolo­gists, it could be eight kilometres shorter still. The Franz Josef is a dramatic exem­plar of the speed of current change. It’s also consistent with the climate models that scientists have been publishing for a decade, models that also predict more intense storm events, drought and a metre of sea-level rise.

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The calculations were based on a projection that the Earth would come close to a 2°C increase in average temperature, a tipping point that at the time was deemed “catastrophic”. Today, however, a 2°C increase appears to have been accepted as the lowest end of expectations, with the latest projections forecasting between 3.7°C and 4.8°C higher temperatures on average.

And yet we blunder on. Instead of reduc­ing greenhouse gas emissions, we have allowed them to accelerate—they grew more quickly between 2000 and 2010 than in each of the three previous decades. Emissions over the past decade were nearly 70 per cent higher than in the late 20th century. Half of all our greenhouse gas emissions since 1750 have occurred in the past 40 years.

The retreat of a few New Zealand glaciers is merely an unfortunate side effect for tourism, but the implications for Earth’s climate and our future are frightening.

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It was by studying glaciers, and the evi­dence they left in the landscape, that 19th-century European scientists first became aware of how dramatically Earth’s climate has oscillated over geological time. In July 1837, the Swiss naturalist Louis Agassiz vividly captured what the new knowledge was revealing. Expected to present a paper to the Swiss Society of Natural Sciences on his specialty, fossil fishes, Agassiz instead confounded the gathered members of the society with a hastily prepared lecture on palaeoclimates. In it, he intro­duced a new word to the world: Eiszeit—‘Ice Age’. His contention was that glaciers had once spread across Europe in a vast ice sheet that extended from the North Pole to the Mediterranean Sea. Coming as it did more than 20 years before the publication of Charles Darwin’s Origin of Species, Agassiz’ address was not well received by an audience still debating whether the Earth was more than a few thousand years old and with a lingering fondness for inter­preting geology in terms of the biblical flood. But Agassiz, a recent convert to the ice-sheet hypothesis, persevered with his climate evangelism and three years later, in the book Études sur les glaciers, he offered a defining image of what we tend to think of as the Ice Age:

“The development of these huge ice sheets must have led to the destruction of all organic life at the Earth’s surface. The ground of Europe, previously covered with tropical vegetation and inhabited by herds of great elephants, enormous hippopotami, and gigantic carnivora, became suddenly buried under a vast expanse of ice covering plains, lakes, seas and plateaus alike.

The silence of death followed…springs dried up, streams ceased to flow and sunrays rising over that frozen shore…were met only by the whistling of northern winds and the rumbling of the crevasses as they opened across the surface of that huge ocean of ice.”

It’s now clear that Agassiz was right— 20,000 years ago, glacier ice blanketed much of the land’s surface and ice sheets and ice floes covered perhaps half of the world’s oceans. Today, we are partway through an interglacial that began 12,000 years ago, at the start of the Holocene epoch. Interglacials are relatively short-lived spikes of warm conditions that periodically inter­rupt the far longer ice ages. The present ice age, the Quaternary glaciation, is itself quite young, having begun about 2.6 million years ago—previous ice ages have lasted for up to 50 million years.

Though the processes that cause gla­cials, and those that free the world from their grip, are still not entirely understood, most scientists now accept that the astro­nomical rhythms of our solar system, oper­ating on vast time scales, generate the underlying pulse. Superimposed on these cycles are a dizzying array of climatic influ­encers and feedback mechanisms that amplify or distort that pulse. A rise in tem­perature can thaw permafrost in the high latitudes of Siberia, Canada, Alaska and Greenland, releasing methane, a gas which powerfully increases the greenhouse effect; reduced ice cover over land and sea reflects less sunlight into space, warming the planet, which further reduces ice extent and promotes even more warming.

At the top of the Baker Glacier on the eastern side of the Main Divide, Brian Anderson and Lawrence Kees measure ice thickness using ground-penetrating radar, part of a GNS study to determine climate over the past 400 years.
At the top of the Baker Glacier on the eastern side of the Main Divide, Brian Anderson and Lawrence Kees measure ice thickness using ground-penetrating radar, part of a GNS study to determine climate over the past 400 years.
Adélie penguins huddle in driving snow at Cape Bird on Ross Island, Antarctica. Behind, the Bird Glacier slithers into the Ross Sea, where it melts rapidly. Many glaciers on the mainland, fed by the massive West Antarctic Ice Sheet, remain ‘underpinned’ by the Ross Ice Shelf, which slows their melting, for now.
Adélie penguins huddle in driving snow at Cape Bird on Ross Island, Antarctica. Behind, the Bird Glacier slithers into the Ross Sea, where it melts rapidly. Many glaciers on the mainland, fed by the massive West Antarctic Ice Sheet, remain ‘underpinned’ by the Ross Ice Shelf, which slows their melting, for now.

Some mechanisms, such as the stately movement of tectonic plates, which through the aeons has variously inhibited or enabled ice formation at the poles, are massive and well understood; others are only recently identified and not yet fully investigated. Climatology in all its forms is a researcher’s El Dorado.

In February 2014, for example, the journal Nature Climate Change published the findings of a team led by Matthew England, a professor of climatology at the University of New South Wales, that attrib­uted the ‘pause’ in surface global warming since 2001 to unusually strong Pacific trade winds. These winds, which blow east to west, are said to have increased the ocean’s ‘overturning circulation’, forcing warm water down to depths of 300 metres or more in the western Pacific while, to the east, cooler water rose. The journal reported that feeding the effect of higher-velocity winds into the climate model gave an equivalent of 0.1˚C–0.2˚C of surface cooling, which almost entirely offset the observed slowdown in global warming.

The same month, the journal Nature carried research by other scientists sug­gesting that the scent of pine forests may also have an effect on warming. The trees emit vapours, which form small aerosol particles that may cool the climate by reflecting solar energy back into space and by helping clouds to form. The researchers noted, though, that if climate change per­sists, and the trees become stressed through heat or lack of water, they will stop giving off the ameliorating vapour.

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Under these various influences, the climate was due to dip back into a new ice age in a few thousand years, ice spreading “sterile and lethal, across the land”, accord­ing to maverick astronomer Sir Fred Hoyle, unless something “monumental” were done about it.

It’s now evident that we have collec­tively risen to Hoyle’s challenge, and done something monumental. Against the odds, we have persevered in our taste for central heating, fast cars and overseas holidays to the point where we ourselves have become, literally, a force of nature.

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“When looking at human agency, we need to keep the time scale in perspective,” says Mackintosh. “Year-to-year occurrences should not be what people focus on. The United States had a bitterly cold winter this year and the blogosphere was alive with comment. But that’s a weather event, not climate.”

For the past 12,000 years, Earth’s climate has been relatively stable. At times, it was slightly warmer or cooler, says Andrew Mackintosh, and our mountain glaciers track that. The previous interglacial 120,000 years ago was similar—perhaps a degree or two warmer than today, and with sea level a little higher. Separating them from the ice age proper was a sustained transition of just 5˚C. A further temperature nudge will even­tually bring us into unknown territory­ planetary conditions never before experienced by humans.

One of the best places to discover where such warming may take us is Antarctica. New Zealand scientists are working there on a range of projects to better understand the continent’s past behaviour and how the future may unfold. The importance of its two ice sheets cannot be exaggerated. Together they contain around 90 per cent of the fresh water on the planet. If the sheets were to melt, sea levels would rise 58 metres.

The West Antarctic Ice Sheet is smaller than the East Antarctic Ice Sheet, but poten­tially more dangerous. Classed as a marine-based ice sheet, its fringes form floating ice shelves—the Ross and Ronne ice shelves and outlet glaciers that drain into the Amundsen Sea—and its bed, which is below sea level, slopes downward inland. Any ice retreat would, in theory, make it vulnerable to total collapse. New satellite data suggests that the massive ice sheet is already begin­ning to show signs of instability.

Peaks of the Transantarctic Range protrude like broken teeth from the polar ice cap in Victorialand. The range, which bisects the continent, divides the East Antarctic Ice Sheet from its troublesome twin, the West Antarctic Ice Sheet, which feeds a multitude of glaciers flowing into the Ross and Amundsen Seas.
Peaks of the Transantarctic Range protrude like broken teeth from the polar ice cap in Victorialand. The range, which bisects the continent, divides the East Antarctic Ice Sheet from its troublesome twin, the West Antarctic Ice Sheet, which feeds a multitude of glaciers flowing into the Ross and Amundsen Seas.
Meltwater runs in blue veins from the Koettlitz Glacier over the McMurdo Ice Shelf toward Mt Discovery. The dark ribbons absorb solar radiation more readily and promote further melting of the underlying shelf, a feedback process which has already wrought dramatic changes to the Ronne Ice Shelf on the opposite side of the Antarctic Peninsula. Scientists are concerned that if the ice shelf were to break up, the glaciers they pin back would advance more rapidly, leading to the collapse of the West Antarctic Ice Sheet, dramatically raising sea levels.
Meltwater runs in blue veins from the Koettlitz Glacier over the McMurdo Ice Shelf toward Mt Discovery. The dark ribbons absorb solar radiation more readily and promote further melting of the underlying shelf, a feedback process which has already wrought dramatic changes to the Ronne Ice Shelf on the opposite side of the Antarctic Peninsula. Scientists are concerned that if the ice shelf were to break up, the glaciers they pin back would advance more rapidly, leading to the collapse of the West Antarctic Ice Sheet, dramatically raising sea levels.

We all know how spectacularly fast such an event can be because we have lived through one. Between January 31 and March 7 2002, to the astonishment of the watching world, the Larsen-B Ice Shelf on the east coast of the Antarctic Peninsula disintegrated entirely. A huge shelf, 3250 square kilometres in area and 220 metres thick, it had been stable since the begin­ning of the Holocene 12,000 years ago. The way in which it disappeared had never been seen before. Typically, polar ice shelves diminish through a combination of surface melting and iceberg calving. Larsen-B simply shattered and drifted out into the Southern Ocean. It was a major wake-up call for the scientific community.

To better understand ice-shelf behav­iour, in 2006 a team of researchers from New Zealand, the United States, Germany and Italy began extracting sediment cores from beneath the McMurdo Ice Shelf and in McMurdo Sound. First proposed by Professor Tim Naish, a project leader at the Institute of Geological and Nuclear Sciences in Lower Hutt, the ambitious Antarctic Drilling Project (ANDRILL) faced technological difficulties, including drilling through 150-metre-thick floating ice in water more than 800 metres deep.

Despite the obstacles, the team bored the two deepest drill holes in Antarctica to get their samples, one of them penetrating more than 1280 metres below the sea floor. The resulting cores, each containing some 1200 metres of sediment, carried an almost unin­terrupted 17-million-year record of Antarctica’s climate. By analysing the sedi­ment and the spore and pollen microfossils that it contained, the scientists could extract from the record a chronology of atmospheric conditions and corresponding responses of the ice going back millennia.

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At the extreme limit of that timescale, Antarctica’s climate was similar to that of the present-day South Island. And at a point around 3.5 million years ago, the holy grail, a record of the atmosphere that matched current projections for the year 2100— carbon dioxide at 400 parts per million and the temperature around 3ºC warmer. Within the sediment and spores, entangled in the matrix of ice, emerged the nightmare scenario: At that time, the Southern Ocean was 6ºC warmer and totally ice-free, the Ross Ice Shelf—almost the size of France­ had entirely disappeared, the West Antarctic and Greenland Ice Sheets had collapsed and the global sea level was at least 10 metres higher, possibly 20.

The ice had uttered a grim warning, and if the past is a useful guide to the future, it had rendered all previous projections woe­fully conservative. The fate of the West Antarctic Ice Sheet will add metres to esti­mates, and dramatically alter the future tenability of coastal land the world over.

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The mechanisms of the Antarctic ice sheets were so poorly understood that their effects were omitted from previous reports of the United Nations Intergovernmental Panel on Climate Change (IPCC), but in light of the sobering data from ANDRILL, there’s a new emphasis on the integrity of the ice shelves that physically underpin the margin of the great ice sheets and stop them sliding, unrestrained, into the Southern Ocean. Scientists are scrambling to quan­tify the inputs, model the outcomes and, importantly, agree on a timescale that reflects the unprecedented speed of change that we’re witnessing. This process, however, is riddled with scientific complex­ity, particularly in terms of determining the influence of oceanic currents.

For starters, researchers wanting to know the temperature or salinity of currents that run beneath the vast Ross Ice Shelf must first drill through the ice and send down instru­ments or a remote-controlled submersible. Resourcing this sort of research is costly, says Mackintosh, but critical.

“The flow of water under that ice is largely what’s going to determine the future of the shelf, because if the ocean starts to warm, it’s a very powerful mecha­nism for melting ice.”

A lack of knowledge about what happens beneath the ice shelf, as well as about the topography of the bedrock under the gla­ciers, how wind systems and currents are likely to change and how that change is likely to manifest itself at the ice-sheet margins, means that the existing ice-sheet models are not yet accurate.

Researchers work in a drilling tent on Roosevelt Island on Antarctica’s Ross Ice Shelf. By extracting ice cores more than 700 metres deep, they can read the history of Earth’s climate like a book, focusing in this case on a period just 20,000–60,000 years ago.
Researchers work in a drilling tent on Roosevelt Island on Antarctica’s Ross Ice Shelf. By extracting ice cores more than 700 metres deep, they can read the history of Earth’s climate like a book, focusing in this case on a period just 20,000–60,000 years ago.

The science becomes more complicated still around the Antarctic Peninsula, the world’s fastest-warming region, which has seen a 3˚C rise over the past 50 years, during which it lost some 25,000 square kilometres of ice shelf. Some researchers, for example, have pinned the demise of the Larsen-B on a strengthening of the westerly winds that blow over the Southern Ocean—behaviour governed by competing forces of greenhouse gases and a recovering ozone hole.

“No one can say which effect will prevail,” says Associate Professor James Renwick of Victoria University’s School of Geography, Environment and Earth Sciences. “This has only been worked out in the past five years.”

The outcome could matter a great deal if, as some climatologists now suggest, the expansion and contraction of the westerlies has played a major role in ice-age cycles. Currently, the Southern Ocean is warming and beginning to approach carbon-dioxide saturation—the world’s largest carbon sink may nearly be full.

To measure how close the oceans are to saturation, scientists refer to the Argo pro­gramme, begun in 2000. A collaborative partnership between more than 30 coun­tries, Argo measures water temperature, salinity and currents using some 3500 small robotic probes scattered throughout the world’s oceans. These drifting floats are programmed to drop to 2000 metres every ten days and take readings as they rise. New Zealand is a committed Argo par­ticipant. Indeed, the National Institute of Water and Atmospheric Research’s vessel Kaharoa has deployed more of these buoys than any other vessel.

It’s estimated that the oceans have absorbed more than 90 per cent of the heat that has been added to the climate system by the action of greenhouse gases over the past 50 years. Argo data shows that deep water—below 700 metres—has warmed unexpectedly since 2000. If, or when, the ocean stops absorbing additional heat from the atmosphere, the torch is likely to be turned up further on Antarctica.

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Nancy Bertler collects old ice. In Gracefield, Lower Hutt, the associate pro­fessor has a freezer room full of it, safe at minus 35˚C, that she is keen for me to see. So there, at the National Ice Core Research Facility at GNS Science, I help her lift out one of perhaps a hundred identical poly­styrene chests. Bertler unclips the tight­fitting lid and removes it. Inside, wrapped in plastic sleeves, lie metre-long cylinders of ice, each the thickness of a drainpipe. Needless to say, the ice is special. The label on the sleeve closest to me reads, “RICE 687”, indicating that, not too long ago, it lay more than two-thirds of a kilometre beneath the ice dome of Roosevelt Island in Antarctica.

A 130-kilometre-long stretch of land that is completely ice-covered, Roosevelt Island sits at the eastern edge of the vast Ross Ice Shelf. Over two four-month field seasons, members of the New Zealand-led Roosevelt Island Climate Evolution (RICE) project took a 764-metre-deep ice core there, drilling 20 hours a day. For the job, they used an electro-mechanical drill based on a proven Danish design but modified and assembled under the direction of New Zealander Alex Pyne, who happens to have been the drill site manager for ANDRILL. Now they’re piecing together the world’s most “high-resolution” view of how the ice shelf responded to past climate change. If ANDRILL revealed how it behaved over millions of years, RICE aims to take just the past 20,000–60,000 years and slice it more finely to discover how fast the ice retreated and under what conditions. In other words, to come to a better under­standing of its climatic sensitivity.

In the polar setting, ice domes are the perfect place to take samples because there is very little ice movement, says Bertler. Domes near the Pole have beautiful “diamond dust” deposits and carry hemi­spherical or global climate signals, whereas those on the fringes of the Antarctic ice sheets have storm-driven deposits.

“New Zealand specialises in working on the coastal deposits, which are more sensi­tive to the interaction of ice sheet, ocean and atmosphere. The record is not as long but the detail is greater because the snowfall is higher, trapping more data, so they comple­ment the inland domes nicely,” says Bertler.

The ANDRILL programme illustrated the scale of sea-level rise that could be expected when the West Antarctic Ice Sheet melts. “But how quickly did it happen?” asks Bertler. “Over a hundred years? A thousand? The goal of our research at this facility is to answer that and so find a proxy for how fast it might happen now.”

In the last interglacial, the sea level rose four metres relative to today, but two metres of that couldn’t be explained. It now appears that the missing two metres came from the collapse of the West Antarctic Ice Sheet. At that time, atmospheric carbon dioxide was only 280ppm, says Bertler, meaning that the ice sheet may be even more sensitive to warming than was thought just a few months ago.

“A significant portion of the West Antarctic Ice Sheet is grounded up to 2000 metres below the sea surface. These are the sectors most vulnerable to ocean warming and have the power to lift sea level by one to two metres. If that happens this century, it will be a tremendous challenge for poli­cymakers—we’re already expecting a metre or more by 2100 as a result of thermal expansion and melt.”

The power of the ice sheet to influence sea-level rise is staggering, and scientists are using every available tool to learn what may lie in store for the planet. As a result of this and other studies, projections are changing by the month.

A massive iceberg takes the brunt of the Southern Ocean swell off the Antarctic Peninsula, where warming is occurring more rapidly than anywhere else on Earth. The rate at which bergs calve off ice shelves is largely governed by the temperature, wind patterns and currents of the seas around them.

Working at the National Ice Core Research Facility, the international team of RICE scientists can extract a surprising amount of information from what looks like nothing more than refrigerator ice. Aerosols, dust from other continents, in fact, every­thing in the environment is preserved—the isotopic composition of particulates even indicating whether they came from distant rice paddies or a swamp. Trace elements, rare earths, lead, cobalt can all be measured in parts per quadrillion. Antarctica, it turns out, is a very good recorder.

The ice is first measured for electrical conductivity, which gives an early indica­tion of its age and signals any volcanic erup­tions or large climatic transitions. Then sections of ice are cut for analysis, much in the same way as a log is sectioned into planks. Some samples are placed on a gold-coated continuous melter, and water and gas from the uncontaminated inner part of the core are drawn off separately for testing.

“Seeing the record evolve right in front of your eyes as the ice melts is exhilarat­ing,” says Bertler. “And even though we have some answers, the most interesting data is in the final 300 metres of core samples. We will finish processing that between June and August this year.”

What distinguishes Bertler’s ice cores from other geological records is that they contain trapped bubbles of air. These pris­tine samples of the atmosphere as it existed many thousands of years ago can tell us how much carbon dioxide, or nitrous oxide or other greenhouse gas was in the air at the time the snow fell. Stable isotopes in the sample record the corresponding cli­matic and ocean temperature.

“What we find is that the temperature rose first, as a result of Earth’s changing position relative to the sun. Then green­house gases released from thawing north­ern hemisphere swamps, and changes in the world’s oceans further amplified that heating effect. While it takes a long time to plunge the globe into an ice age, these fast amplifiers mean that ice ages end rather more abruptly.”

Weighing all the evidence, it seems that this time around, largely due to human activities, climate change has taken a short­cut. Carbon dioxide has increased, and feedback mechanisms—melting perma­frost, reducing snow cover—have fuelled further releases of greenhouse gases. Not only that, but it’s happened not in the depths of an ice age, but in the middle of an interglacial period when temperatures are already high.

Humans, in other words, have derailed the greatest of Earth’s natural systems. It remains to be seen how well we’ll deal with the consequences of that. But from the evi­dence of New Zealand’s South Island gla­ciers, and the coded messages buried in Antarctic ice, the outlook may be worse than any of us had expected.