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Glaciers continue to show significant ice loss

14 September 2008

Glaciers continue to show significant ice loss

New Zealand’s glaciers are showing the lowest total ice mass on record and most are continuing to shrink at a rapid rate.

Research released by the National Institute of Water & Atmospheric Research (NIWA) shows the Southern Alps glaciers have lost 2.5 km³ (2.2 billion tonnes) of permanent ice from April 2007 to March 2008, the fourth highest annual loss since monitoring started.

The 2008 total ice volume estimate for the Southern Alps glaciers of 44.9 km³ is the lowest on record.

For the past 32 years NIWA has been surveying 50 glaciers in the Southern Alps, using a small fixed wing aircraft, to record the height of the snow line at the end of summer.

NIWA Principal Scientist Dr Jim Salinger says the photographs taken on this year’s survey showed the glaciers had lost much more ice than they had gained during the past glacier year.

“As a result of La Niña conditions over New Zealand, more easterlies, and warmer than normal temperatures, there was less snowfall in the Southern Alps and more snowmelt.

The higher the snow line, the more snow is lost to feed the glacier. On average, the snow line this year was about 130 metres above where it would need to be to keep the ice mass constant,” Dr Salinger says.

Dr Salinger says these results match trends of ice mass lost globally. International monitoring of mountains glaciers by the World Glacier Monitoring Service in Switzerland shows most glaciers are retreating. Of the glaciers where continuous data is available, the mean annual average loss in ice thickness since 1980 is close to half a metre per year.

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Background information:

1. Worldwide, glaciers are regarded as a useful indicator of global warming, but New Zealand’s glaciers are more complicated because they have their source in areas of extremely high precipitation. West of the Main Divide in the Southern Alps, more than 10 metres (10 000 mm) of precipitation falls each year as clouds are pushed up over the sharply rising mountain ranges. This means the mass and volume of New Zealand’s glaciers is sensitive to changing wind and precipitation patterns as well as to temperature. So, for example, the glaciers advanced during most of the 1980s and 1990s when the area experienced about a 15% increase in precipitation, associated with more El Niño events and stronger westerly winds over New Zealand. The glaciers in parts of Norway are similar.

2. Despite the sensitivity of New Zealand glaciers to changes in both precipitation and temperature, the volume of ice in the Southern Alps dropped by roughly 50% during the last century. New Zealand’s temperature increased by about 1 °C over the same period.

3. Globally, most glaciers are retreating. Of the glaciers for which there are continuous data from the World Glacier Monitoring Service, the mean annual loss in ice thickness since 1980 remains close to half a metre per year. The Service has said that the loss in ice mass “leaves no doubt about the accelerating change in climatic conditions”. For world glacier data, see www.geo.unizh.ch/wgms

4. The level of the glacier snow lines is not necessarily closely related to the amount of snow that falls on the country’s ski fields during winter. Most of the popular ski fields are east of the Main Divide, or in the North Island. Mount Hutt, for instance, gets its snow from big southeasterlies, whereas most of the glaciers are fed by westerlies.

ENDS

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