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Brendon McMahon, Local Democracy Reporter
Franz Josef Glacier has dramatically shrunk 500m in the past five years due to the “shocking” rise in ocean temperatures, a glacial expert says.
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 September 21.
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.
Fox Glacier is continuing to retreat. Photo / Niwa
“Since the Westland Tai Poutini National Park plan was notified in 2018, the glaciers have retreated another 500m. It is hard to keep up,” Anderson said.
It was a direct reflection of climate change, Anderson 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 Brian Anderson has been monitoring the South Island glaciers. Photo / Victoria University
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.
“Right now some pretty crazy things are going on.”
New Zealand’s glaciers were mostly on the West Coast, with most within protected national parks or gazetted wilderness areas.
The most northern, the Rolleston near Otira along with the furthest south in the region, Brewster at Haast, were regularly measured.
Anderson said Franz Josef Glacier has 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 was 40 years ago before an “extraordinary advance” of more than 1.5km over the next 25 years when 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.
Anderson noted that 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 at least 200 glaciers in the region that had vanished.
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 no snow left on them.
“One hot year can undo previous years of growth because the glaciers are really sensitive to warming temperatures.”
