NZ glaciers smallest on record

TREVOR CHINN

WARMING SIGN: Marion Glacier in Arawata Valley has recently withdrawn from its proglacial state. Most of New Zealand's glaciers are the smallest they've been since records began.

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Most of New Zealand's glaciers are now the smallest they have been since records began - and they continue to shrink at a rapid rate.

The National Institute of Water and Atmospheric Research, which made the discovery, said global warming was the main culprit.

Between April last year and March this year, glaciers in the Southern Alps lost about 2.2 billion tonnes of permanent ice - the equivalent in weight to the top section of Mt Taranaki. It is the fourth highest annual loss since monitoring began 32 years ago.

The total ice for the glaciers now comprises an estimated 44.9 cubic kilometres - the lowest on record. The volume of ice dropped by 50 per cent during the last century.

Niwa principal scientist Jim Salinger said glaciers were fed by snow, but because of the La Nina weather system over New Zealand, more easterly winds and warmer than normal temperatures during the period, there was less snow in the Southern Alps and more snowmelt.

Dr Salinger said while the glaciers were sensitive to changes in wind and precipitation as well as temperature, global warming was a big factor in their shrinking.

"It's one of the clearest signs that our climate is warming and that [the shrinkage] is a definite physical response. To have that amount of melting you would have to reduce the precipitation at least by a half or more or warm a degree," he said.

"We know that precipitation has not gone down in the Southern Alps. In the last quarter of a century it's gone up. So to make them retreat you've got to have more melting, which is higher temperatures.

"This is certainly a definite sign of warming in the New Zealand area."

Niwa has surveyed 50 glaciers in the Southern Alps for the past 32 years, recording the height of the snowline at the end of each summer. On average the snowline this year was 130 metres above where it would need to be for the glaciers not to shrink, Dr Salinger said.

It was unlikely the glaciers would disappear entirely, as that would require a temperature rise of 7 degrees celsius and no snow even at the top of our highest mountain, Mt Cook.

But they would continue to retreat. Another sign of warming were 12 glacial lakes, including ones at Marion Glacier and Tasman Glacier.

"They are definitely a sign of warming. There is no doubt about it. You get a very rapid loss of snow and ice and that's what's been happening."

- © Fairfax NZ News