New Zealand's glaciers have again suffered one of the worst melts on record, scientists say – and it's doubtful they'll get the top-up they desperately need before summer.
Data being analysed by a team of researchers shows a dismal trend of shrinking glaciers across the Southern Alps only continued during the country's third warmest summer.
Under climate change, many of these icy wonders could vanish completely, while others would become much higher and harder for people to reach.
Being highly sensitive indicators of atmospheric temperature and precipitation levels, glaciers are regarded by scientists as coalmine canaries in a warming world.
It's believed climate change has partly caused New Zealand's glaciers to shrink in total volume by one third in just four decades of observations.
The biggest melt came amid New Zealand's record-hot summer of 2017/18 and the freak marine heatwave that accompanied it – leaving the glaciers still depleted in the face of more unusually warm land and sea temperatures last summer.
While the most recent annual aerial survey of the Southern Alps' snowline was still being studied, scientists expected last season's ice mass loss fell within the five worst.
Some of the smaller glaciers had been especially hard hit.
One glacier on Mt Wilson, in Arthur's Pass, had been reduced to two puny snowpacks, while another atop Mt St Mary, near Lake Ohau, had disappeared completely.
The amount of ice that vanished from the Brewster Glacier, near the Haast Pass, was also among the highest since the 1970s, Victoria University PhD student Lauren Vargo said.
"The loss wasn't as dramatic as the previous year, but this does suggest that these high mass loss years are becoming the norm."
This animation shows how different Brewster Glacier is now compared to just a few years earlier in 2016! pic.twitter.com/ZJevKylYKB— Lauren Vargo (@DrLaurenVargo) July 11, 2019
A 3D model that Vargo was building would ultimately reveal whether the trend had been uniform across all of the glaciers – and how much of it can be blamed on human-driven climate change.
But she added that, even without the new data, it was still known that changes in glacier mass were mainly driven by shifts in temperature and precipitation.
Glaciers needed the right balance of both to survive – and this year, so far tracking as the fifth warmest, hadn't delivered what was required for good snowfall.
Niwa forecaster Ben Noll said there was potential for some snow at the end of winter – but likely not enough.
"Some of these places have been running at a large deficit. If you look at southern Canterbury and northern Otago, they've had basically next to no rainfall this winter," he said.
"While there is a signal for a relatively active spell of winter in the second half of August or September, in terms of snow and rainfall, bringing it all the way back to what you'd expect would be a challenge."
Climate scientist Professor Jim Salinger – who has calculated the Southern Alps lost nearly a 10th of their total ice volume over 2017-18 – said if the long-term trend continued, snowlines would continue to climb.
He said the shifts had implications not just for skiing and tourism, but also for farming.
"We'd see more water flowing down the rivers during the winter, but less in summer, which is beneficial for hydro generation, but not so good for irrigation."
Victoria University glaciologist Dr Huw Horgan said it was possible that a few years of decent snowfall could help the glaciers recover – but that assumption ran against the long-term trend of warming.
"We can link that all of the way through to emissions – we've got to keep those temperatures down if we want these glaciers to survive."
One scenario that assumed future warming could be limited only to another 2C - the ultimate goal of the Paris Agreement on climate change - would mean glaciers would keep retreating but would stabilise by the middle of the century.
But if emissions continued to ramp up without any efforts to curb them, glaciers could become virtually unrecognisable by 2100.
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.