Nearly a third. That’s the amount of ice lost from New Zealand’s glaciers since 2000. Almost 300. That’s the number of individual glaciers that have vanished forever since we started monitoring them regularly about half a century ago.
According to a recent global assessment, New Zealand ranks third after the European Alps and the Caucasus, in Eastern Europe, in the proportion of glacial ice lost to rising temperatures. And the glaciers that remain are now melting at an accelerating pace.
In early March, I witnessed the changing icescapes of the Southern Alps first hand when I joined glaciologists on their annual snowline survey. Each year, the team flies across the mountaintops to photograph 50 glaciers and their snowline − the demarcation line between the remains of the winter’s snowpack and exposed glacial ice.
The snowline tracks the impact of warming, says Andrew Lorrey, a climate scientist at Niwa who has been organising the surveys for the past 15 years. “In years with a slightly cooler summer, the snowline will be lower and we’ll have more snow remaining. But in warmer years, the snowline climbs up and more of the glacier is exposed.”
A glacier would be in balance if winter snow equalled summer melt, he says. But the surveys show that summer melt now exceeds snowfall during winter and “we’re seeing the glaciers’ terminus and sides, the whole body, diminishing.”
Glaciers are the compressed snowfall of centuries past. They are defined as ice masses large enough for gravity to pull them downhill. During the 1970s, pioneering glaciologist Trevor Chinn completed an inventory of New Zealand’s glaciers, counting 3144. He selected 50 that were representative in size and elevation and, in 1978, started photographing them from the air each year to keep track of their shape. The annual slowline flights mean New Zealand has one of the world’s longest-running and most comprehensive glacier monitoring programmes.
Most of the glaciers that have disappeared were small and thin or low-lying and therefore more vulnerable to warming temperatures. Much of the country’s mountain ice is contained in a few larger and better-known glaciers close to Aoraki Mt Cook, including the Tasman, Fox and Franz Josef. All of them are now shrinking and retreating fast. The snowline has moved up by 200m on average since the start of the surveys, Lorrey says. During particularly warm years it moved “right off the top of the mountain”, leaving the entire surface of a glacier exposed.
Brewster Glacier, in Mt Aspiring National Park, is among the larger bodies of ice that have been photographed each year since the surveys began, but it’s also one of two glaciers that are monitored in more detail. Each November, glaciologists climb the Brewster to measure the thickness of the snowpack and to drill stakes 10m deep into the glacier. They return at the end of summer to measure and retrieve the parts of the stakes exposed by melting of the snow and underlying ice.
This year was really hard, says Lauren Vargo, glaciology research fellow at Victoria University of Wellington’s Antarctic Research Centre. “The more melt, the more stakes you have to collect. I don’t think I could have carried any more stakes.” Her analysis of the aerial images and directly measured melt rates shows the Brewster has shrunk by 24% in area and lost 17m in thickness between 2016 and 2024. “On one hand, when I see these dramatic changes, there’s this validation for doing the research. But then you think of what it means, for glaciers around the world, in terms of sea-level rise and the water resources they hold … and it can get quite scary.”
