Visitors are running out of time to see New Zealand’s dwindling southern glaciers, which are becoming a safety hazard.

The central Southern Alps has lost a quarter of its ice in recent decades, and stands to lose another 50 to 60 per cent.

It meant its spectacular glaciers were shrinking at an unprecedented rate, some having lost several kilometres of ice this century.

It was a topic discussed at the Sustainable Summits conference at Mt Cook this week.

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An iceberg in Lake Tasman.

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In recent years, the largest glaciers – including Fox, Franz Josef, and Tasman – have attracted increased tourist interest while continuing to shrink.

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Tourists pose for a photo on the Tasman Glacier.

Hundreds of tourists visit the glaciers each day. There were 40,000 visitors to Lake Tasman at the base of Tasman Glacier last year.

The lake did not exist in the early 1970s, but is now seven kilometres long and deeper than Lake Pukaki – the result of the glacier’s severe retreat. The lake will expand substantially over the next decade.

Witnessing the shrinking glaciers in their current glory could soon become a relic of the past, glaciologist Dr Brian Anderson said.

“It’s not a good story,” he said.

“These glaciers are going to get really small – it’s quite scary.”

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Lake Tasman with Aoraki/Mt Cook in the background. The lake will expand substantially as the glacier retreats.

He used mathematical models to predict the future size of glaciers under various warming scenarios.

If current warming trends continue, the three largest glaciers will likely become a fraction of their original size by 2100.

Franz Josef Glacier on the West Coast had among the fastest melt rates measured anywhere in the world, he said.

By the end of the century, nearby Fox Glacier will have retreated up to five kilometres and lost nearly 40 per cent of its mass.

Because both glaciers are dynamic, there will likely be years in which they advance, but the long term trend will be severe retreat.

ALDEN WILLIAMS/FAIRFAX NZ

A Heliworks Squirrel AS-350 on Tasman Glacier.

“[Advance years] will still happen in the next century, but we’ll still see the same overall picture of more and more retreat.

“Whatever we do about our emissions is going to make a big difference to these places because they’re so sensitive to temperature. A difference of half a degree, for these glaciers, is quite a lot.”

The glaciers were important for tourism, but the effects of their retreat had led to unstable rock walls and other hazards, Anderson said.

“The glacier’s moving, it’s retreating, the hillside’s coming down . . . but at the same time those things are happening there’s hundreds of people visiting.

“It’s actually a real struggle to manage these sites safely, with a lot of visitors and very real hazards.”

Pedestrian access to Fox and Franz Josef glaciers was banned last year because they had receded too far to access on foot. 

They can now be visited only by helicopter, requiring an adjustment for the Department of Conservation (DOC) and local operators.

“We’re now putting 30,000 [helicopter] landings a year into Westland [Tai Poutini] National Park,” DOC director-general Lou Sanson said.

“We’ve got to allow more glacier landings, we’ve got to do it in the park planning process, and we’ve got to do it without annoying climbers who also value the space.

“These are tricky decisions that we constantly have to work through.”

 – Stuff