Franz Josef Glacier has advanced 50m since last December, after retreating some 1.4km since 2008. Photo / Getty Images
Franz Josef Glacier has advanced 50m since last December, after retreating some 1.4km since 2008. Photo / Getty Images
New Zealand's glaciers have shrunk in area by one third since over the past four decades - an astonishing loss scientists have partly attributed to climate change.
The new figures, just presented to an international conference, come as a glaciologist has warned an abnormally hot summer could mean trouble for the South Island's icy giants.
Dr Sabine Baumann, of the Technical University of Munich, Germany, recently completed the first complete stocktake of New Zealand's glacier cover since Dr Trevor Chinn made an aerial survey in 1978.
Franz Josef Glacier. Photo / Supplied
The work drew on remote sensing technology, along with field work that helped distinguish the glaciers' physical area size, which could be camouflaged to satellite imaging by heavy debris cover.
Her results, reported to the American Geophysical Union, revealed how the total glacier area had shrunk from 1240 sq km to 857 sq km - a decrease of 31 per cent since the late 1970s, or just under one per cent of loss each year.
The number of glaciers also fell slightly from 3283 to 3180, while mean altitude climbed from 1859m to 1939m above sea level.
Those figures followed a 2014 analysis by Chinn and other scientists which showed ice volume in the Southern Alps had shrunk by 18.4cu km or 34 per cent since the 1970s, and ice losses had been accelerating rapidly since the turn of the new century.
Victoria University glaciologist Dr Brian Anderson said glaciers responded to climate of a variety of timescales - anywhere between a few years and centuries.
"So most of the glaciers are still retreating because of warming during the 20th century, and particularly since 2007," he said.
Fox Glacier. Photo / File
"But some of our most responsive glaciers are actually advancing, likely a response to slightly positive mass balances measured from 2013 to 2015."
Franz Josef Glacier, after retreating 1.43km between 2008 and December 2016, had advanced around 50m.
Image / Supplied
"That's still tiny compared to the amount that's been lost, but at least it now appears to be going in the right direction."
However, a La Nina-flavoured summer bringing consistently hot weather and warm sea surface temperatures in the Tasman Sea could have significant impacts.
"The super-warm November has melted back a lot of snow in the mountains, but we can't really say until the end of the summer what the overall effect on the glaciers will be.
Image / Supplied
"But if the projections are correct, and we are in for a long, hot La Nina summer, then it will certainly be a year where the glaciers lose a lot of mass."
Whether the overall trend of ongoing loss continued was dependent on how the world acted on climate change.
One scenario that assumed future warming could be limited only to another 2C - the ultimate goal of the Paris Agreement on climate change - would see glaciers keep retreating but stabilising by the middle of the century.
But if emissions continued to ramp up without any efforts to curb them, glaciers could become virtually unrecognisable by 2100.
Around the world, glaciers were already melting at an unprecedented rate, losing on average between half a metre and metre of ice thickness every year.
"The message there is we do have some real choices about our future," Anderson said.
Meanwhile, he and colleagues were planning to deploy instruments in front of the Franz Josef Glacier, in the hope it would eventually advance over top of them.
"We'd like to measure the water pressure under the glacier and understand how that links to motion," he said.
"But it's kind of speculative, because who knows how much further it's actually going to advance."
