Southern Alps glacier loses enough ice to supply NZ with three years' worth of drinking water

Southern Alps glacier loses enough ice to supply NZ with three years' worth of drinking water

A boat full of people drives closely to interesting glacial ice formations.

A glacier in the Southern Alps has lost enough ice over the past three years to supply New Zealanders with drinking water for the same period.

Brewster Glacier is estimated to have lost 13 million cubic metres of ice in those three years - damage that's putting New Zealand's glacier tourist attractions on a path to extinction.

During the same period, at other end of the country, seasonal extremes swung Auckland from experiencing the wettest autumn on record to one of its most severe multi-season droughts, NIWA climate scientists' Andrew Lorrey, Ben Noll and ARC's researcher Lauren Vargo wrote in a piece on their findings.

The ice loss was calculated by Lauren, who has pioneered 3D digital modelling techniques to track New Zealand ice volume changes.

The researchers say the ice lost from Brewster Glacier is only a small part of the Southern Alps ice storage, which has been declining since annual monitoring of the glaciers began in the late 1970s.

"The staggering thing is that it's just one small glacier," said Lauren.

Andrew said he's never seen anything like it in his career.

Aerial surveys each March have tracked the loss of about 30 per cent of the Southern Alps' ice volume over the past four decades, the equivalent of about 16 trillion litres of water, they said.

This year's annual survey - completed a few weeks before lockdown - found the situation looking a little better, with more snow on the South Island glaciers than the previous two years.

But Andrew warned a few "good snow years" could not be considered any kind of recovery against an overall trend of increasingly warm temperatures, saying it would take 20-30 years like this to start to reverse the damage. He said the damage sustained by some small glaciers between 2018 and 2019 has pushed their snow lines above the tops of their mountains and placed them on a path to extinction.

This year, red ash and dust from Australian bushfires was sprinkled over the Southern Alps ice, absorbing more solar radiation and increasing the potential for melting.

Andrew says the thousands of photos taken of glaciers during each annual survey are growing more important because of climate change and the role the glaciers play in New Zealand's water cycle.

Overseas, Italy is going to extremes - wrapping a glacier in a 100sqm tarpaulin.

"It's not really a realistic way to stop large-scale glacial melt," Lauren said. "It's just something that can be done for individual glaciers."