New Zealand’s glaciers lost 2.5 km3 (2.2 billion tonnes) of permanent ice from April 2007 to March 2008, leaving 44.9 km3 of ice in the Southern Alps – the lowest amount since NIWA began regular surveys 32 years ago. The picture (credit: “Mr Ice” Trevor Chinn, click for larger image) shows the Marion Glacier in the Arawata Valley in South Westland which has recently retreated above its proglacial lake. The annual survey uses a fixed wing aircraft to record the height of the snowline at the end of summer (and Trevor gets to take the pix). Jim Salinger, NIWA’s principal scientist, says that the survey shows that the glaciers had lost a lot more ice than they had gained over the preceding winter [press release]:
â€œAs a result of La NiÃ±a 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.â€
More below the fold…
The graph shows the change in glacier ice volume since the NIWA survey began in 1976. The 2008 loss was the fourth largest in the record.
From NIWA’s background notes:
Worldwide, glaciers are regarded as a useful indicator of global warming, but New Zealandâ€™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 Zealandâ€™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 NiÃ±o events and stronger westerly winds over New Zealand. The glaciers in parts of Norway are similar.
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 Zealandâ€™s temperature increased by about 1 Â°C over the same period.
And even though Mt Hutt has had a record snow season, NIWA note:
The level of the glacier snow lines is not necessarily closely related to the amount of snow that falls on the countryâ€™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.
[Update 15/9: Jim Salinger was on press duty yesterday, handing out quotes to the local media, and in so doing invented a new unit of measurement - the Rangitoto - to be used when explaining large volumes to Aucklanders.]
[Update 2: Jim's been kind enough to send me a copy of a recent article from NIWA's magazine: Glacier response to climate change, Salinger, Chinn, Willsman & Fitzharris, W&A 16 (3) 2008 (2.8MB PDF) which goes into more detail about NZ glaciers in a warming world.]