Temporary break' for NZ glaciers won't save them. Video / Supplied
New Zealand's gradually melting glaciers have fared slightly better this summer, despite receiving a dusting of ash from Australia's bushfires.
But scientists say the comparative increase in snow should only be seen as a temporary break, rather than any good news on the climate change front.
Niwa and Victoria University of Wellington scientists completed the annual end-of -summer snowline survey of 50 South Island glaciers yesterday, taking thousands of photographs to evaluate the snowline altitude and build 3D models of the glaciers.
These will be used to assess how much of the previous winter's snow has remained covering each glacier to contribute toward long-term glacial ice accumulation.
The scientists also documented widespread ash coverage on the glaciers as a result of the Australian bushfires.
The snowline survey began in 1977 and provides an incredibly valuable long-term record of how New Zealand's glaciers have retreated over time due to climate change.
Scientists estimate about 30 per cent of New Zealand's ice that was catalogued in the late 1970s has been lost in the past 40 years.
The past two years of the snowline survey have seen the impact of particularly harsh conditions imposed on our glaciers, with marine heatwaves and record temperatures taking their toll.
Niwa climate scientist Dr Andrew Lorrey says although the glaciers looked a lot better this year than the past two years, it could not be considered any kind of recovery.
"You would need to see 20 to 30 years like this one to even start to consider whether the recent damage that has been done can be reversed to any degree," he said.
Glaciers can take a very long time to grow. I am not at all heartened by what looks like a decent snowline this year – it is part of climate variability, and some good years are to be expected.
"Every now and then you will get a year that reminds you of how things used to be, but the overall trend is towards more frequent hotter years, which are hugely detrimental to glaciers."
Scientists estimate about 30 per cent of New Zealand's ice that was catalogued in the late 1970s has been lost in the past 40 years. Photo / Niwa
Yesterday ash from the Australian bushfires was still highly visible across most of the glaciers since it first settled there in early January.
Lorrey said ash had coloured many glaciers light orange and may have contributed to the annual melt process.
"At this stage it is difficult to characterise exactly how much the ash has added to the ablation of snow and ice, but there should be some immediate negative effect."
Victoria University of Wellington's Dr Lauren Vargo will use the photographs from the survey to construct 3D models of the glaciers in a process called structure from motion photogrammetry.
The methods being pioneered by Vargo will assist year-on-year comparisons and allow accurate calculations of how recent seasonal snow and older ice are changing.
"What we are seeing is a clear trend now - retreating glaciers and a steady loss of ice." The scientific results from this year's survey will be known later this year.
By the numbers
• 31%: As at 2017, New Zealand's total glacier area had shrunk from 1240sq km to 857sq km - a decrease of 31 per cent since the late 1970s, or just under 1 per cent of loss each year. • 1939m: The number of glaciers also fell slightly from 3283 to 3180, while mean altitude climbed from 1859m to 1939m above sea level. • 34%: Those figures followed a 2014 analysis which showed ice volume in the Southern Alps had shrunk by 18.4cu km or 34 per cent since the 1970s, and ice losses had been accelerating rapidly since the turn of the new century. • 0.5m: Around the world, glaciers are melting at an unprecedented rate, losing on average between half a metre and metre of ice thickness every year.
