Higher than average temperatures and low
rainfall could have contributed to the loss
of glacier mass.
New Zealand’s glaciers lost significant ice mass again last summer.
The National Institute of Water & Atmospheric Research (NIWA) has just released the results of its annual end-of-summer survey of the snowline on key South Island glaciers, showing continued loss of glacier mass.
The survey uses a small fixed wing aircraft to fly over 50 glaciers in the Southern Alps and Kaikoura. Scientists take photographs and then analyse the images to determine the position of the snowline after the summer melt but before the first winter snowfall. This provides an index of the mass balance or ’health’ of the glaciers of New Zealand. The survey has been going since 1977.
NIWA Snow and Ice Scientist Dr Jordy Hendrikx says weather patterns over the course of the year from April 2008 to March 2009 meant that overall the glaciers had lost much more ice than they had gained. This was mainly due to the combination of above normal temperatures and near normal or below normal rainfall for the Southern Alps during winter, and La Niña-like patterns producing more northerly flows creating normal-to-above normal temperatures, above normal sunshine, and well below normal precipitation for the Southern Alps particularly during late summer.
The higher the snowline, the more snow is lost to feed the glacier. On average, the snowline this year was about 95 metres above where it would need to be to keep the ice mass constant. This indicates that the loss of glacier mass observed in 2007-08 has continued.
When studying and reporting what is happening to glaciers, it is important to look at more than one factor. The position of the end of summer snowline is only part of the story; in New Zealand, an estimated 90 per cent of ice loss from glaciers since 1976 is due to down-wasting and lake calving. NIWA’s snowline surveys show an overall decrease in the glacier mass balance (and thereby volumes) over the past 33 years – but this is punctuated by periods where the prevailing weather conditions caused the glacier mass balance to increase for a few years.
Similarly, glacier terminus position (the “length” of a glacier) can be misleading when considered on its own because total volume can be decreasing even while terminus length is increasing.
Editor's Note: Original news release can be found here.