New Zealand's famous glaciers are looking "sad and dirty" after another brutally warm summer, says a scientist who took part in this year's aerial stocktake.

Each year, the Niwa-led snowline survey checks the health of about 50 glaciers across the Southern Alps.

After the record-hot summer of 2017-18, scientists were struck by how many mountains had been stripped of ice and snow.

The latest flight, undertaken last week, and following New Zealand's third warmest summer, found many of the glaciers still in a sorry state - and some had disappeared altogether.

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"I'd say it was unimpressive - in fact, it's quite concerning… sad and dirty is still the story," Niwa climate scientist Drew Lorrey said.

"Last year, the vast majority of glaciers had snowlines that were off the top of the mountain, and this year, we had some where we could see snowlines on, but they were very high.

"On the first day of our survey, we observed 28 of them, and only about six of them had what I would call a snowline."

He was particularly concerned that some appeared to have receded around upper edges.

"If you are removing that nucleus up at the highest point of the mountain, and then you start to add stuff on over winter and strip it back during summer, there's really nothing there for it to get added on to that's robust."

Glacier fluctuations were among the clearest signals of climate change, because they were highly sensitive indicators of atmospheric temperature and precipitation levels.

Scientists believe it was a warming planet that had partly caused New Zealand's glaciers to shrink in total volume by one third in just four decades of observations.

Lorrey didn't expect some of those smaller, hardest-hit glaciers would survive much longer.

One glacier on Mt Wilson, in Arthur's Pass, had been reduced to what he described as two "puny" snowpacks.

"When I started going on the survey about 10 years ago or so, it was still there. Now, it's nope, nothing there."

Another glacier atop Mt St Mary had also vanished.

"Some of these glaciers were very small to start with, but now we have ice packs that are just melting away."

Lorrey expected the impact of warmer sea surfaces on local climate – especially the freak marine heatwave that engulfed New Zealand over the summer of 2017-18 – were much to blame for the recent melt.

"That we had warmer water around the northern two thirds of the country over decent stretches of this summer played a big part," he said.

"And last year, when those sea surface temperature anomalies in the Tasman Sea stretched further south, well that was absolutely killer, because the effect reaches up to altitude and then dictates what's going on with air temperature."

The survey was the first in 40 years without glaciologist Trevor Chinn, who began making the aerial stock takes in the 1970s, and died in December at the age of 81.

Chinn's legacy was a unique and invaluable dataset that offered an independent measure of how climate change and variability affected New Zealand's water resources.

"He gave us excellent training and he set us on this path of having long-term observation data that's unbroken – and it's an amazing way to track what's going on with our cryosphere and climate," Lorrey said.

A lack of snow cover on the Southern Alps after New Zealand's third hottest summer was clearly apparent. Photo / Drew Lorrey
A lack of snow cover on the Southern Alps after New Zealand's third hottest summer was clearly apparent. Photo / Drew Lorrey

The team hadn't been the only one to notice the sorry state of many glaciers.

One group of Swiss scientists who recently visited as part of a global survey said some of the smaller glaciers appeared to be decaying at a faster rate.

Research recently presented by climate scientist Professor Jim Salinger indicated that, over 2017-18, the alps experienced their biggest snow melt on record, losing about 9 per cent of their total ice volume.

Lorrey however said Niwa and Victoria University were yet to report the official data.

Other figures, reported to the American Geophysical Union in 2017, revealed how New Zealand's total glacier area had shrunk from 1240 sq km to 857 sq km - a decrease of 31 per cent since the late 1970s, or just under 1 per cent of loss each year.

The number of glaciers also fell slightly from 3283 to 3180, while mean altitude climbed from 1859m to 1939m above sea level.

Victoria University glaciologist Brian Anderson takes a photograph during an aerial survey of the Southern Alps. Photo / Drew Lorrey
Victoria University glaciologist Brian Anderson takes a photograph during an aerial survey of the Southern Alps. Photo / Drew Lorrey

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.

Whether the overall trend of ongoing loss continued was dependent on how the world acted on climate change.

One scenario that assumed future warming could be limited only to another 2C - the ultimate goal of the Paris Agreement on climate change - would see glaciers keep retreating but stabilising 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.

Around the world, glaciers were already melting at an unprecedented rate, losing on average between half a metre and metre of ice thickness every year.

This year's survey team included Niwa climate scientist Gregor Macara, Dr Brian Anderson, Dr Ollie Wigmore and Lauren Vargo from Victoria University, and pilots Andy Woods and Aaron Duff of Milford Sound Scenic Flights.