The Franz Josef Glacier is a steep, fast-moving glacier on the West Coast that has retreated, advanced and then retreated again over the last century. Photo: RNZ / Tess Brunton
Franz Josef Glacier has dramatically shrunk 500m in the past five years due to the "shocking" rise in ocean temperatures, an glacial expert says.
And in the past 30 years, 200 glaciers in the Southern Alps have disappeared altogether, Victoria University glaciologist Brian Anderson of Ross said.
"It's not a very happy story [and] they are getting a lot smaller," he told the West Coast Conservation Board.
Dr Anderson presented an update on his ongoing observation work on the Southern Alps glaciers - particularly those in the Westland Tai Poutini National Park - as the board met in Hokitika on 21 September.
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He outlined the climatic factors at play in the ongoing huge glacial decline, and the consequent impact on recreation and tourism activities important to South Westland.
"Since the Westland Tai Poutini National Park plan was notified in 2018, the glaciers have retreated another 500m. It is hard to keep up," Dr Anderson said.
Some of the sites where glacier guide concession areas were operating when the current national park plan was approved in 2018 were no longer present due to the dramatic retreat of Franz and Fox glaciers, he said.
It was a direct reflection of climate change and it was happening now, he said.
"One of the main drivers of glacier change in the Southern Alps is ocean temperature."
The year 2016 was the hottest on record, but 2023 is "off the chart", he said.
"The last two years we've had these marine heatwaves. This is the crucial thing that drives glacial change."
He noted a Poutini Ngai Tahu tradition, spoken of by Poutini author Paul Madgwick, of the glaciers being reflected in the surface of the sea.
Dr Anderson said this traditional picture was true in the current context.
"The reason I like that is the glaciers really are a reflection of the sea."
The known changes in the global climate system directly correlated to what was happening with the glaciers including the huge loss of sea ice in the southern ocean, he said.
"Sea ice is closely linked with what happens in the Southern Alps - in 2023 it is very, very low."
Dr Anderson said that fact alone was "shocking" and equated to four times the land area of New Zealand "missing".
"Right now some pretty crazy things are going on."
He noted this country's glaciers were mostly on the West Coast, with the bulk within protected national park or gazetted wilderness areas.
The most northern, the Rolleston near Otira along with the furthest south in the region, Brewster at Haast, were under regular measurement.
Dr Anderson said Franz Josef Glacier had the "longest and best" record of length measurement in the Southern Hemisphere - meaning its remarkable advances and retreats were well documented.
A low point for Franz had been 40 years ago before the "extraordinary advance" of growth over about 1.5km over the next 25 years where it reached a peak in 1998.
"The biggest profile it had was in 1998."
But more extraordinary was the dramatic "full speed retreat" from around 2017 on.
Dr Anderson noted that in the same period, over about 30 years, some Westland glaciers such as the Victoria had either retreated a long way "or have just gone".
This included the Ivory in the Waitaha headwaters and there was a list of at least 200 glaciers in the region that had vanished.
Dr Anderson said a crucial question for Franz Josef was always if there was enough ice moving down from the top to make up for the melt at the bottom and over time it had always advanced.
But what was happening now was marked by more dynamic effects over short periods, for instance where the glacier had retreated by 70m in one year.
Canterbury University associate professor in glaciology Heather Purdie said some of the disappearing glaciers may be small and not be named.
Sometimes in the warmer years, she has been to look at the glaciers and found there is no snow left on them.
"One hot year can undo previous years of growth because the glaciers are really sensitive to warming temperatures."
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