The Final Meltdown
Retreating glaciers and thinning snow and ice are the future of New Zealand’s mountains. Climate researchers are seeking to predict what will change, and when. The Deep South National Science Challenge is taking a lead role in helping decision-makers plan for the coming century.
Retreating glaciers and thinning snow and ice are the future of New Zealand’s mountains. Climate change is predicted to warm the country’s atmosphere by 1-4°C by the end of the century, altering the natural water cycle - how much is frozen as snow, how much falls as rain, and how much flows in rivers. Climate researchers are seeking to predict what will change, and when. What will be the impact on hydroelectric power stations and irrigation schemes? Which areas will be hit hardest by flooding, or increasingly severe drought? The Deep South National Science Challenge is taking a lead role in helping decision-makers plan for the coming century.
Professor Andrew Mackintosh, ARC Director and one of Climate Scientists on board the annual end-of-summer snowline survey. Over two days, the research team, led by NIWA and including scientists from universities around the country, observe glaciers from Fiordland to Arthur’s Pass to see how the ice has fared over the preceding year. The survey has been conducted since 1977, and has produced an enviably long - and globally significant - dataset on glacier behaviour in a time of climate change.
Mackintosh is leading a project to predict the future of these glaciers - research which has brought together the country’s leading snow and glacier scientists for the first time, under the banner of the Deep South National Science Challenge.
The snowline survey was started by New Zealand’s doyen of glaciologists, Trevor Chinn, who has personally eyeballed all of this country’s 3153 glaciers. Chinn was responsible for the first glacier inventory in New Zealand, which took him 10 years to complete. He subsequently chose the 50 index glaciers that are tracked annually by the snowline survey. He has lived through times of glacier advance, and now he watches their retreat.
This year has been a bad one, he tells me at his home in Lake Hāwea. A temperature anomaly in the Tasman Sea in late 2017 and into 2018 resulted in a marine heatwave, with sea-surface temperatures averaging two degrees warmer than normal, and on the West Coast spiking up to six degrees warmer than average. The effect on glacial melt over the summer was profound.
“This season is the worst we’ve ever seen,” says Chinn. “Almost half the glaciers have lost all the snow they gained during the previous winter, plus some from the winter before that. There are rocks sticking out everywhere. The meltback is phenomenal.”
When Chinn started the glacier inventory in 1977, the purpose was to update the country’s topographical maps with accurate positions of glaciers and provide estimates of the area and volume of permanent snow and ice. But after a few years of flying and photographing retreating glaciers, he realised something more important was at stake. He wasn’t just mapping, he was monitoring how the mountains were changing, and his photographs were a record of a changing climate.
There is no more reliable indicator of climate change than a glacier, says Chinn. The annual change of ice volume, known as the glacier’s mass balance, is the sum of all climate processes. “You can’t argue with a retreating glacier.”
Not all years are as bleak for glaciers as 2018, but the bad ones tend to stick in scientists’ memories. NIWA Climate Scientist, Andrew Lorrey remembers his first negative mass-balance year, 2011. There had been a strong La Niña, with strong highs over the South Island, and more frequent northerly and easterly winds. The glacier tongues and their associated snowfields were grimy brown. Ablation had been severe over the summer, and the ice looked sick.
Will this be the new visual appearance of alpine New Zealand, I ask him: besmirched snow, grey rock where ice used to be, faded glory?
“With climate change, the dice are definitely loaded,” he says. “In the past, natural multi-decadal patterns of climate variability sometimes aligned with the warming trend, and sometimes went against it. Now it seems as if the variability is mostly going in the same direction. It’s like putting a concrete block on the accelerator of climate change.”
Lorrey says the 2018 survey, with its debris-covered snow, glacier lakes growing in size, and ice retreating upslope, feels like a foretaste of what is to come. But he adds that New Zealand’s climate is variable enough that there will probably be years when snow accumulates and the mass balance of the glaciers tweak into the positive side of the ledger. At those times, the ice will wear a fresh white face.
Trevor Chinn has named only one glacier in New Zealand - compared to nearly 50 in Antarctica - but it remains his favourite. Ivory Glacier, its name a riff on a nearby mountain, The Tusk, provided Chinn with the data he needed to calculate a glacier’s ice volume by measuring its area.
Chinn worked on the Ivory from 1968 until 1975. In those days, he says, the glacier had a marvellous ice-filled cirque and a tiny patch of water at the tip of its tongue. Today, that water is a lake, with blue ducks living on it, and the glacier is a tiny patch, high up on a bare mountainside.
This could be the future for all New Zealand glaciers, but for some it will happen a lot faster than others. Large valley glaciers are covered with a thick layer of rocky surface moraine that acts as a thermal blanket, insulating the underlying ice. For these, retreat will be decades slower than for steep, debris-free glaciers such as the West Coast’s Fox and Franz Josef.
Predicting the fate of such glaciers is by no means straightforward, says Mackintosh, also a lead author of a forthcoming Intergovernmental Panel on Climate Change (IPCC) special report on the links between melting ice and rising oceans. In order to model the behaviour of a debris-covered glacier, you need to know the exact distribution of debris, how thick it is and what its thermal properties are - most of which is unknown, and difficult to measure.
Despite such data gaps, Mackintosh and fellow ARC glaciologist Brian Anderson have developed some trajectories for New Zealand’s glaciers over the coming century. He shows me two visualisations: one based on the IPCC’s most dire climate pathway, in which greenhouse-gas emissions continue to rise throughout this century, and the second based on the IPCC’s most optimistic alternative, in which emissions peak by 2020 and decline substantially afterwards.
Under the first scenario “Burn it all and damn the consequences”, as he puts it - most of New Zealand’s ice has disappeared by 2100.
“The tongues of Fox and Franz Josef have gone completely. There’s just a little bit of healthy ice left on top of Aoraki, plus a few debris-covered glaciers like Tasman, where the upper part that used to provide the snow and ice has gone, the lower part has been eaten away by the lake, and you’re left with a slug of debris-covered ice in the middle. That’s one possible future.
“But if we follow the declining-emissions pathway - drawing carbon out of the atmosphere, reducing the carbon budget to zero, limiting warming to two degrees above pre-industrial temperatures - then the glaciers get about 30 per cent smaller, but we end up, at the end of the century, with something not dissimilar to what we have today. Franz and Fox, though greatly diminished, still exist. They’re still recognisable features of the mountain landscape, still icons of the Southern Alps. It’s a fundamental difference: keep the glaciers or lose them. This is what’s at stake.”
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