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Glaciers Lost Ice Mass In Past Year

5 September 2006

Glaciers Lost Ice Mass In Past Year

The Southern Alps glaciers monitored annually by NIWA lost ice mass in the year to March 2006.

NIWA has surveyed 50 glaciers for the past 30 years using a small fixed wing aircraft to record the height of the snow line at the end of summer. Principal Scientist Dr Jim Salinger says analysis of photographs taken on this year’s survey in March showed the glaciers had lost much more ice than they had gained during the past glacier year.

This is because much less snow fell in the Southern Alps as a result of more anticyclones over New Zealand, especially over July – December 2005. During this six month period, the anticyclones produced milder and drier conditions. Over winter 2005, temperatures were above average. These conditions produced less snow, especially in winter, and the warmer than normal temperatures for the remainder of the year resulted in early snowmelt.

‘This year (2005–06) stands in contrast to the gains that have occurred in the previous three glacier years (2002–03, 2003–04, and 2004–05),’ Dr Salinger says.

‘The higher the snow line, the more snow has been lost to feed the glacier. On average, the snow line this year was about 50 metres above where it would be to keep the ice mass constant.’

The effects of this past (2006) winter are not included in the survey, but may result in a gain in glacier ice mass by March 2007, depending on conditions over this coming summer.

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Background

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 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 25–30% 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.

Change in glacier ice mass since NIWA survey began

Trends upwards represent growth in glacier ice mass and trends downwards represent loss in ice mass. The advances seen during most of the 1980s and 1990s are related to about a 15% increase in precipitation, associated with more El Niño events and stronger westerlies. The advances in 2003–2005 reflect another period of higher precipitation.

This graph shows changes in the end of summer snowline for the Southern Alps, compared with the average over the 30 year period surveyed so far. Bars up represent higher snowlines (and loss of ice mass) and bars down lower snowlines (and gains in ice mass).

ENDS

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