Melting moments
New Zealand’s mountain glaciers are vanishing. They have shrunk by nearly a third since the 1970s and could be gone by the end of the century unless we move quickly towards zero emissions. And, as they retreat, we are losing more than ice.
New Zealand’s mountain glaciers are vanishing. They have shrunk by nearly a third since the 1970s and could be gone by the end of the century unless we move quickly towards zero emissions. And, as they retreat, we are losing more than ice.
Flying over the Southern Alps’ icy mountain tops in March last year, Trevor Chinn, widely regarded as the godfather of New Zealand glaciology, was busy taking pictures of every glacier below. It was the worst melt he’d seen in the 40 years since he started monitoring the snow line – the thin boundary between glacial ice and snow – at the end of each summer. “There are rocks sticking out everywhere – the meltback is phenomenal,” he said at the end of the annual flyover. That flight was to be his last bird’s-eye view of New Zealand’s glaciers. Chinn died in December 2018, aged 81, a few days after suffering a stroke while looking up the latest research at his home at Lake Hāwea.
The summer of 2018 was New Zealand’s hottest on record. A marine heatwave in the Tasman Sea, with sea temperatures 6-7°C above average in places, pushed unusually warm air up the mountains. More than half of the 51 mountain glaciers monitored during each snow-line survey lost all the snow that had fallen during the preceding winter, plus some from previous years.
Glaciers are the compressed snowfall of centuries past. They are dynamic, always changing as they accumulate snow in winter and lose some of it to melt in summer. But as the world warms, this annual balance is tipping in favour of melting – and the result is a net loss of ice.
In the four decades since the first survey, New Zealand’s glaciers have lost a third of their ice. The snow line has moved up by an average of 3.7m each year. Some have retreated up valleys they once filled; others have recoiled into basins or are breaking up into smaller blocks. Some have disappeared. Over the coming years and decades, those that remain stand to lose another 50-60% of ice.
In March this year, after New Zealand’s third-hottest summer on record and three months after Chinn’s death, a team of glaciologists flew the survey again. The results are still being analysed, says PhD student Lauren Vargo, and they may not be as bad as last year. “But it is still probably one of the years with the least amount of snow, in the top two or three years, since records began in 1977.” Vargo is part of a new generation of glaciologists who continue to track the shifting snow lines and perimeters of glaciers at each summer’s end, taking hundreds of images to build a three-dimensional model of New Zealand’s alpine icescape. One part of her PhD, at Victoria University of Wellington, is to develop methods to quickly and accurately assess the loss of ice. Another is to determine how much of it can be attributed to climate change.
The summers of 2018 and 2011 stand out as “extreme events” – by now a familiar phrase to describe occurrences that should be rare but are becoming more frequent in a warming world. “Our simulations show that the extreme mass loss measured at Brewster Glacier in 2018 could only have occurred with modern human influence,” Vargo says. The ice loss seen at Rolleston Glacier in 2011 was at least 10 times more likely because of climate change. “Some of the things that we take pictures of, that were definitely glaciers when Trevor started the survey, you’re unsure of now. There’s sort of a minimum size for a glacier and a lot of these are dropping below that. If you were describing them now, you wouldn’t bother naming them.”
Drew Lorrey is a climate scientist at the National Institute of Water and Atmospheric Research (Niwa), which runs the snow-line surveys. During this year’s flight, he was taking thermal images and “soaking in a lot more of the landscape around the perimeter of the glaciers”. He worries that as the edges of glaciers thin, even years with good snowfall won’t undo the damage because the snow has nothing cold to nucleate on. “The blanket is falling onto a different material. I was noticing, around the fringes, some pretty severely damaged glaciers, especially small ones and the ones that terminate into very small pro-glacial lakes.” He wondered: “How fast is this taking off from us?”
In the 1970s, Chinn described 3155 glaciers in the original survey. Realising that it would be impossible to keep an eye on all of them, he identified 51 index glaciers, including New Zealand’s famous tourist magnets on the West Coast, Fox and Franz Josef, and Tasman Glacier at Aoraki/Mt Cook, which are now all retreating fast.
“Glaciers of various sizes constitute some of that original catalogue,” says Lorrey. “And we may have lost upwards of 750 of them. That’s not an inconsequential amount of ice, but that’s what we’re dealing with here.”
THE HUMAN FACTOR
As with anything affected by climate change, the future of New Zealand’s glaciers will depend on how quickly and effectively we act to start curbing emissions in the next few years. Andrew Mackintosh, a glaciologist who recently moved to Monash University in Melbourne but has spent years studying New Zealand’s rivers of ice, says in a world that doesn’t warm more than 2°C above preindustrial conditions, New Zealand will still have glaciers, but they will be much shorter.
If we keep going as we are, “we expect the majority of ice will be gone by the end of the century.”
If we keep going as we are, “we expect the majority of the ice will be gone by the end of the century, with just a few small glaciers occupying the highest peaks”.
Mackintosh was part of a team studying the South Island’s West Coast glaciers during the 1990s and early 2000s, when, for a while, they bucked global trends and advanced. “They were bulging at the front … and then that changed dramatically,” he says. “One type of a negative mass balance year is that you have a reasonable amount of snow still sitting on the upper part of a glacier but the area of ice melt is much larger than the area of snow. What we’ve seen recently is that everything is gone – and that’s a really bad sign for a glacier.”
Whether the rate of glacial wasting will continue to accelerate remains to be seen, but, says Mackintosh, “in the last decade, there have been many more negative years and we’re on a steep trend of losing ice”.
ECONOMIC THREAT
Alpine ice is vanishing across the world, and the rate of mass loss during the early 21st century is unprecedented. The most obvious consequence is sea-level rise. Between 1961 and 2016, non-polar mountain glaciers lost more than 9000 billion tonnes of ice and their melt lifted the oceans by 27mm. But in New Zealand and elsewhere, we are losing more than ice.
The road to Fox Glacier is now closed indefinitely. Engineering reports found no practical way of rebuilding it after floods destroyed it in February. A month later, torrential rain and floods ripped open an old Westland District Council dump site, washing hundreds of tonnes of rubbish down riverbeds and along the coast. Then the Waiho Bridge, south of Franz Josef, folded in on itself after a one-in-20-year storm bloated the river.
The bridge was rebuilt and the rubbish cleaned up, but the risks remain. The acting chairman of the West Coast Tai Poutini Conservation Board, Keith Morfett, told RNZ’s Nine to Noon that as the Fox Glacier retreats, the walls of its canyon become unstable. “Mill Creek area is essentially a mountain of loose rock that’s been destabilised by retreating ice. So, in an intense storm event, that slip has the potential to become a river of rock … and nothing will stand in its way.”
The Government announced a $3.9 million package, funded by the international visitor tourism and conservation levy, to develop cycle and walkways to glacier viewing points and Lake Gault so that “tourism continues to benefit communities”. About one in 10 jobs in the Westland district depends on visitors. The quarter of a million people who come to the area each year contribute about 20% of the region’s GDP.
Less than 15 years ago, it was relatively straightforward to walk to the Fox terminus and up on to the glacier, says Heather Purdie, who was a guide then but has since turned her love of the mountains into a research career at the University of Canterbury. Once the glaciers began their retreat,
The Mill Creek area “has the potential to become a river of rock and nothing will stand in its way”.
the risk of rockfall increased and made the area unsafe for walkers. Franz Josef lost walking access in 2012, and Fox followed in 2014. Guiding companies switched to relying on helicopters to ferry visitors to higher elevations.
Purdie says receding ice and exposed moraine walls are making mountain access more challenging for recreational climbers as well. In some places, the melt can outpace efforts to monitor the changing landscape.
Rolleston Glacier, on Mt Philistine in Arthur’s Pass, is one of two New Zealand glaciers (together with Brewster) with a comprehensive programme to track their mass balance beyond the images collected during the annual aerial surveys. Purdie is using stakes and snow pits to track how much snow falls and melts again. “We dig the snow pit at the same spot every year to make the data comparable, but in the past two summers, we didn’t have any snow to dig.”
LOSS OF HABITAT
Snow and ice are more than physical aspects of the landscape; they provide habitat for plants and animals that are highly adapted to the cold, many of them unique to New Zealand. Earlier this year, a research team from the Swiss Federal Institute of Technology visited the Southern Alps to study microbial ecosystems – the unseen worlds that could be disappearing with the ice before we even understand them. Expedition leader Mike Styllas chose New Zealand as the first stop on a three-year itinerary that will take in 15 countries and 200 glaciers because of the decades of observations gathered since the 1970s.
When I joined Styllas’ team during a field trip to Richardson Glacier, near Aoraki/Mt Cook, I could see the retreat path the debriscovered tongue of ice has carved into the landscape. It left a smaller tributary, once connected to the ice flow, stranded above a rocky ridge. The Charity Glacier now sends a gushing melt stream down the rocks. “The Richardson valley and glacier exhibit exactly the characteristics that we’re looking for,” Styllas told me. “The glacier has been monitored for a long time, so we know how much it has retreated, and the valley itself has smaller alpine glaciers that tend to vanish faster.”
Styllas, a Greek mountaineer who spent 15 years climbing and guiding in some of the world’s highest mountains, draws inspiration for his research from Mt Olympus and the changes its degrading glacial ice has wrought on the landscape from summit to sea. Few people have studied the microbiomes of alpine glaciers, Styllas says, but these microscopic habitats seed conditions for the rest of the alpine environment.
In New Zealand, the alpine band between the tree and snow lines covers 11% of the country. It is home to endangered species such as the rock wren (one of two surviving species of New Zealand wren) and the superbly adapted alpine cave wētā, which can survive being frozen. The animals and plants that survive in this harsh habitat have evolved from ancestors in warmer parts of the country, but are now genetically distant enough to be considered unique populations. What’s more, 90% are endemic.
These frost-loving communities are a research focus for Trevor Chinn’s son Warren, a conservation biologist at the Department of Conservation.
“With climate change, we have a landscape problem of running out of real estate. We don’t know if they’re going to move up, sideways, stay put and adapt or go locally extinct as a result of either conditions not being favourable or because they are being gobbled up by a new guild of predators they are naive to.”
Until recently, biologists thought that native alpine species were relatively safe because cold winters kept warm-blooded mammals at bay. But stoats are known to roam beyond the treeline and Warren Chinn once found a dead mouse on the 2174m summit of Mt Armstrong, in Mt Aspiring National Park.
As it gets warmer, he says, alpine species seem to be moving up to stay within their comfort zone, but “things that are lower and more adapted to warmer temperatures have moved a greater vertical distance than those that are adapted to colder temperatures”.
The alpine environment has expanded and contracted in the past, and Chinn says it will not disappear entirely. “But the difference is the arrival of mammalian warm-blooded predators that can now survive the winter.”
PEAK WATER
As more ice turns to water, glacial runoff flushes alpine catchments. Niwa’s Lorrey likes to think of glaciers as water towers – huge storage tanks that could take the edge off the extreme winter droughts that are predicted to happen more often, and for longer, in a warming world.
The extent to which melting ice might ease future droughts is one of several questions scientists are tackling as part of a collaboration within the Deep South National Science Challenge. With the help of sophisticated models, they simulate future changes to spring snow melt and summer flows as glaciers are lost.
Worldwide, glacial retreat has triggered concerns about future water availability. Glaciated drainage basins cover about a quarter of land (not including glaciers in Greenland and Antarctica) and millions of people rely on them for drinking water, crop irrigation and hydropower. As glaciers recede, they initially release more water, until that runoff reaches a maximum – often referred to as “peak water”. Beyond
“We may have lost upwards of 750 [of our glaciers].”
this point, water supply from glaciers begins to dwindle. The European Alps are thought to have gone past this point already, and in mountainous areas of central Asia and South America, this scenario looms as a future water supply threat.
But in New Zealand, glaciers don’t contribute much meltwater to rivers, says Niwa hydrologist Daniel Collins. Snow and rain are much more significant factors, with an average of 550cu km of precipitation falling on the country every year, compared with 40cu km of water still stored in alpine ice. With rising temperatures, precipitation
“You can’t make a glacier lie. They are harbingers of what is happening and what is to come.”
is expected to increase and more of it will come down as rain rather than snow, swelling river flows particularly in winter.
Higher winter precipitation is one of the strongest signals from climate models, says Collins, and it could be good news for hydropower schemes in the South Island, with “increased [water] supply during months of highest demand”.
It’s a different story for irrigation, with projections for decreasing river flows during summer. But there, too, changes to precipitation are a bigger factor than glacial melt, Collins says.
“Glaciers are great and they have many values, but servicing water resources as they are currently used in New Zealand is not one of them.”
For Lorrey, however, glaciers are the most visual indicators of a changing climate. “You can’t make a glacier lie. We know what those glaciers are responding to – they are harbingers of what is happening and what is to come.”