Glaciers in New Zealand’s Southern Alps gained ice mass again in the past year. Fifty glaciers are monitored annually by the National Institute of Water & Atmospheric Research (NIWA).
NIWA’s most recent survey of the glaciers was undertaken in March this year. Dr Jim Salinger of NIWA said today that analysis of the aerial photographs shows the glaciers had gained much more ice than they had lost during the past glacier year (March 2004 – February 2005).
This year’s gains are due to more snow in the Southern Alps, particularly from late winter to early summer 2004. During this five month period, more depressions ('lows') to the southeast of the Chatham Islands brought frequent episodes of strong cold southwesterly winds, and temperatures were 0.6°C below average, producing more snow.
"Over the last three years, the glaciers have gained in mass, halting the declines seen between 1998 and 2002. This past year was the seventh largest gain since we started aerial surveys in 1977," said Dr Salinger. "Since 1977 overall for the Southern Alps there has been little change in size of the glaciers."
"The recent gains do not compensate for the large overall losses seen over the past century. The iconic Franz Josef glacier is still much shorter now than in 1900, and the volume of ice in the Southern Alps dropped by about 25-30% last century. This is linked to an increase in regional mean temperatures of 0.7°C."
Globally, most glaciers are retreating as the Earth warms. 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".
New Zealand’s glaciers are somewhat unusual 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 a year as clouds are pushed up over the sharply rising mountain ranges. This means the mass of New Zealand’s glaciers are sensitive to changing atmospheric circulation and both precipitation patterns and temperature. So, for instance, 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. In most of the rest of the world (with the exception of parts of Norway), glaciers tend to be in areas of lower precipitation, so rising temperatures are affecting the glaciers there more directly and sooner.
Dr Salinger said the annual NIWA flights in March use a small fixed wing aircraft. They record the height of the glacial snow line at the end of summer. "This reveals how much snow the glaciers have lost or gained during the past year. The lower the snow line, the more the amount of snow that has accumulated to feed the glacier. On average, the snow line this year was about 110 metres below where it would be to keep the ice mass constant."
He said the level of the glacier snow lines is not closely related to the amount of snow that might fall 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," Dr Salinger said.
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