Climate change is causing summer snowlines to rise and glaciers to retreat in Aotearoa and Ruapehu's glaciers are no exception according to satellite pictures.
And now a leading climate scientist wants a more comprehensive survey to get a better idea of the state of the glaciers on Mt Ruapehu.
Niwa principal scientist Andrew Lorrey was a member of the End of Summer Snowline team that recently surveyed South Island glaciers from a fixed-wing aircraft over Southern Fiordland to northern Westland and Canterbury.
"We need to survey the North Island glaciers because the last thorough study was done in 1988," he said.
"There were 18 glaciers on Mt Ruapehu that Trevor Chinn defined in the national database."
The late Trevor Chinn was New Zealand's foremost glaciologist who pioneered the End of Summer Snowline method for measuring glacier ice volumes.
"The glaciers were all at least 4 hectares or larger and the largest one on Ruapehu was Whangaehu," Lorrey said.
In 1988 the Whangaehu glacier covered 86.6ha, was 1.85km long, and had an estimated cubic measurement of 17.32 million meters of ice.
It was one of eight glaciers that formerly fed into the Whanganui catchment via Whakapapa.
In the 34 years since there had been partial updates using satellite data from 2002 and 2009 and in 2016 it was estimated that there had been a 25 per cent decrease and only 15 glaciers were located on the North Island.
"It is significant that the glaciers feed into the Whanganui River when you think in terms of the Te Awa Tupua settlement which gives the river legal status as a person," Lorrey said.
"The volume of water that comes from the glaciers may not be that significant but the relationship is important in terms of how we view the mountain in relation to the river."
Lorrey said it was not his place to tell people how they should be protecting the glaciers. However, he was willing to offer some ideas.
"What I do personally is: drive less and use public transport when it is available, try to eat less processed food, and grow food.
"Those are small things that everyone can do to help negate the effects of climate change. People travelling to the ski fields might consider staying longer so they're not driving back and forth if they are using petrol-powered vehicles."
Unseasonably warm autumn temperatures have led to speculation that Ruapehu might have a late start to the ski season this year.
However, Niwa's principal weather scientist Chris Brandalino said it would be premature to give a winter outlook at this stage.
"What I can say is that the ocean temperatures around New Zealand's coastline are warmer than normal for this time of year," he said.
"That doesn't mean that there won't be snow on the mountain in July though. You're looking for that sweet spot - the Goldilocks moment when conditions are just right for snow to fall. If that doesn't happen in time, it should still be cold enough to make snow using the snow machine."
Ruapehu Alpine Lifts (RAL) chief executive Jono Dean said the start of the ski season is still six weeks away and it was far too early to make predictions.
"We are following scientific advice and there is no reason to think we won't have a bumper ski season this year.
"The current warm spell we're having should not be seen as a precursor to a warmer winter," he said.
Another concern for the region has been the recent volcanic unrest on Ruapehu which is currently at alert level 2. The Crater Lake (Te Wai ā-moe) temperature remains stable at 37C.
"In terms of volcanic activity, we are advising all visitors to maintain a 2km distance from the crater lake vicinity which is considered safe at the current level," Dean said.
"The Sky Waka Gondola is 3.5km from the crater area and had been very busy in recent weeks. We had a bumper Easter weekend and there have been plenty of school holiday visitors as well."
Visit Ruapehu's Jo Kennedy said visitor numbers had markedly increased since the country moved to the orange traffic light Covid-19 setting on April 13.
"The school holidays have been really busy and there have been so many cyclists coming through doing the Mountains to the Sea and all the local trails as well," she said.
"We have seen warm spells in autumn before and there was mild weather before the season opened last year."
In 2021, the June temperatures were unusually mild for the time of year but Whakapapa and Tūroa ski fields opened for the season on the first weekend in July and Ruapehu welcomed around 5000 visitors.