NZ snowline shrinks
New Zealand’s glaciers have all retreated and lost volume since NIWA started surveying them in 1977.
Principal environmental monitoring technician Andrew Willsman says the consistent trend is that all index glaciers have lost area since the mid-1970s.
The overall trend is ice loss, which Willsman says correlates with average sea surface temperature. In other words, as seas surrounding New Zealand (especially the Tasman Sea) have warmed, ice and snowlines have receded.
Glacier recession in New Zealand mirrors global trends. The expectation is that the index glaciers surveyed by NIWA will continue to lose ice if temperatures keep increasing.
NIWA’s End of Summer Snowline team (Dr Andrew Lorrey, Andrew Willsman, Dr Trevor Chinn) and colleagues from Victoria University Wellington (Professor Andrew Mackintosh, Dr Brian Anderson, Dr Huw Horgan and PhD candidate Lauren Vargo) survey the snow and ice coverage from the air using fixed-wing aircraft.
The images are analysed to determine the position of the end of summer snowline, used as an estimate for the glacier equilibrium line that marks the amount of warm season melt before the first winter snowfall. The glacier mass balance year – a sum of the annual health of our ice – runs from April through to the following March.
New work being led by VUW researchers who collaborate with NIWA on the summer snowline flight has produced high-resolution digital elevation models from NIWA’s collection of historic ice photos. This effort will help refine the volume of ice change through time, which is important for cataloguing the frozen water resources for New Zealand.
More than 40 glaciers covered during the summer flight –termed index glaciers – are spread across the Southern Alps, from deep in Southern Fiordland to northern Westland and Canterbury. These glaciers were chosen because of their representative span across the alpine region of New Zealand.
Most of the index glaciers surveyed have been found to respond quickly to changes in climate. Many of the smaller glaciers respond quickly to inter-annual changes. Some, however, take many decades to respond because they have a thick layer of insulating rock cover.
The expectation for the 2017-2018 summer, which was tested in early March, is that the snowlines would be higher than average due to very warm Tasman Sea temperatures which, along with warmer than normal air temperatures across New Zealand, are expected to enhance summer melting of alpine ice.
NIWA’s Southern Alps flight surveys form part of the Climate Present and Past project, which looks at recent and historical climate data to track past variability and changes in climate.