Climate change hits southern glaciers
The Garden of Eden and Garden of Allah have been measured for the first time and are retreating because of climate change.
The two magnificently named South Island glaciers about 50 kilometres northeast of Mt Cook are so remote and hard to reach that little research on their size and behaviour has been done.
But University of Otago student Angus Dowson recently finished his Masters of Science thesis trialling new methods to measure the glaciers remotely.
Using satellite imagery gathered almost every day between February 2000 and 2017, Dowson found the two related icefields followed the ‘‘broad response of glaciers in the Southern Alps to climate’’ – meaning they have overall retreated.
Mountain glaciers provide ‘‘some of the clearest and most sensitive environmental indicators of climate change’’, Dowson wrote in his thesis, because their high altitude exposes them to disturbances in regional and global temperatures.
Until now, New Zealand mountain glacier research has largely been done on foot – researchers climbing over the ice with measuring gear – and Niwa’s annual snowline survey.
Going every year since 1978, the annual end-of-summer survey uses small aircraft and and aerial photography to record the permanent snow line – the altitude at which snow remains throughout the year.
This is a proxy for glacier health and whether they are gaining or losing mass.
Dowson’s research accomplished much the same thing, except using satellite data gathered daily.
He used a technique called ‘‘albedo’’, which was recently
‘‘Mountain glaciers provide some of the clearest and most sensitive environmental indicators of climate change.’’
Angus Dowson
developed by Otago University academics Pascal Sirguey and Nicolas Cullen and others.
Albedo measures the light reflected off glacier ice and snow and is a proxy for mass balance, Sirguey said in an interview. The method was calibrated and truthed on Brewster Glacier near Haast.
Brewster is a relatively accessible glacier and researchers have climbed over and aerial photographed it for years. Sirguey, Cullen and others used satellite imagery and albedo to estimate mass and got a good match with the older data.
If New Zealand’s mountain glaciers substantially melted due to climate change, there would be almost no effect on sea levels.
Rather, the loss of the South Island glaciers would likely impact electricity generation in the southern hydro lakes.
Agriculture could also be impacted as irrigators extract water from rivers and aquifers partly charged by glacier water.
The Garden of Eden and Garden of Allah contribute to the Rangitata River on the east coast and the Whanganui and Whataroa rivers to the west.
The trio of researchers climbed these icefields earlier this year. In an interview, Dowson said he was amazed by the scale of the glaciers and their remote, wild beauty.
The Garden of Eden was named in 1934 by AP Thomson, an early mountaineer who was later president of the Royal Society and head of the New Zealand Forest Service. The Garden of Allah was officially named in 1971 in sympathy with the established theme.
The new measurement tool could now be applied to other glaciers, Dowson wrote. The data were collected by the satellite and available for analysis, while new data arrive daily.
While Fox and Franz Josef glaciers are famously retreating, other New Zealand glaciers are advancing. The data are still limited, but ‘‘overall, our glaciers are experiencing retreat,’’ Sirguey said.