A third of the permanent snow and ice on the Southern Alps
has vanished in less than four decades, according to an
analysis of aerial surveys.
In an article published on Australian website The
Conversation, three Kiwi researchers describe the story of
the alps' disappearing ice as very dramatic.
The analysis, by climate scientist Dr Jim Salinger, Otago
University Professor Emeritus Blair Fitzharris and
glaciologist Dr Trevor Chinn, follows on from a paper
published by Dr Chinn last year documenting the retreat of
our postcard glaciers.
Partly using aerial surveys by the National Institute of
Water and Atmospheric Research, the three authors have
calculated the alps' ice volume has shrunk by 18.4cu km or 34
per cent - and those ice losses have been accelerating
rapidly in the past 15 years.
When compared with rapid glacier retreats in many parts of
the world, the loss raised serious questions about future sea
level rise and coastal climate impacts, they said.
In 1977, Dr Chinn began taking aerial photographs to measure
the annual end-of-summer snowline for 50 index glaciers
throughout the Southern Alps, which are still taken by Niwa.
He and his colleagues have now used Niwa results to calculate
the annual glacier mass balance, and to quantify the volume
changes of small to medium glaciers in the alps.
These glaciers responded quickly to annual variability of
weather and climate, and were in balance with the current
But this wasn't so for the 12 largest glaciers, among them
the Tasman and Godley, which had a thick layer of insulating
rocks on top of the ice lower down the glaciers' trunk.
"Their response to new snow at the top is subdued, and may
take many decades to respond," the authors wrote. "Up until
the 1970s, their surfaces lowered like sinking lids
maintaining their original areas. Thereafter, glacial lakes
have formed and they have undergone rapid retreat and ice
To make the calculations, they used the snowline survey data
along with earlier topographic maps and a GPS survey of the
ice levels of the largest glaciers to calculate total
ice-volume changes for the Southern Alps up until this year.
Over that time, they said, the ice volume had fallen by 34
per cent, or from 54.5cu km to 36.1cu km in water
Of that reduction, 40 per cent was from the 12 largest
glaciers, and 60 per cent was from the small to medium-sized
Veteran mountain guide Shaun Norman described their
calculations as astonishing but unsurprising.
An injury in 2000 had kept him off the high alps since then,
but even before, the changes had been visible, he told the
"One could see that less snow dumps in quite a few years
meant pieces of rock which you knew were always covered
suddenly were staying clear for 12 months of the year, and
The World Glacier Monitoring Service estimated the 1890s
extent of ice volume in the Southern Alps was 170cu km,
compared with 36.1cu km now - a change the authors said was
evidence of the local effects of global warming.
Based on regional warming projections of 1.5C to 2.5C, it has
been projected by glaciologists Valentina Radic and Regine
Hock that just7 to 12cu km of ice would remain on the alps by
the end of this century.
- By Jamie Morton of the New Zealand Herald