The big melt: we won't recognise our glaciers

The spectacular tongues of ice on the Franz Josef Glacier have retreated dramatically in just three years, this is the most recent image. Photo / Brian Anderson

By 2100, New Zealand's postcard glaciers will bear little resemblance to how we know them today, a scientist says.

The warning comes as a new global study, published overnight, shows the world's glaciers are melting at an unprecedented rate, losing on average between half a metre and metre of ice thickness every year.

Recent research has already shown how the South Island's Franz Josef and Fox Glaciers, which attract tens of thousands of tourists each year, have retreated by three kilometres and at least between three to four square kilometres in area since the 1800s, with most of the loss happening between 1934 and 1983.

Although there had been small advances at different points, the overall picture was one of melting - and a retreat observed last year was one of the fastest on record.

Dr Brian Anderson, of Victoria University's Antarctic Research Centre, told the Herald there was now little doubt the dramatic retreats seen over the past few decades was the result of anthropogenic climate change.

With predictions that the world's climate will warm by several degrees by the end of the century, this would have a major impact on the icy wonders.

"The glaciers will advance again, because they respond so quickly to even a few years of higher snowfall or lower melt but, given the fact the Earth is warming, its unlikely they will reach their 20th century maxima again," said Dr Anderson, who has calculated the glacier retreat under various warming scenarios.

"They are not going to disappear, because our mountains are so high that there is always going to be some small glaciers on them, but they are really not going to be as recognisable as we know them today.

"For example, we are not going to have the Fox or Franz Josef glaciers with those steep, spectacular tongues coming down into the rain forest.

"The Tasman and the other glaciers on the eastern side of the mountains, meanwhile, are going to respond in a really complicated way that we don't fully understand - but they are certainly going to get a lot smaller too."

Dr Anderson contributed to the latest study by the World Glacier Monitoring Service, published in the Journal of Glaciology, which has compiled worldwide data on glacier changes in more than 30 countries.

When observations from the previous decade were compared to all available earlier data, it was shown that glaciers were losing ice thickness at a rate of two to three times more than the corresponding average of the 20th century.

The study authors found that the present rate of glacier melt was "without precedence" at a global scale - at least for the time period observed and probably also for recorded history - and that the long-term retreat of glacier tongues was a global phenomenon.

The study further indicated that the "intense ice loss" of the past two decades had resulted in a strong imbalance of glaciers in many regions of the world, and these would suffer further loss even if the climate remained stable.