Tourists on Fox Glacier on the West Coast. Photo: supplied / Fox Glacier Guiding
Almost all of New Zealand's glaciers could completely disappear if global warming continues on its current track, new research shows.
Local glacier researchers say that level of loss would contribute to sea-level rise, make water shortages worse, and affect tourism.
The study, published in Nature Climate Change on Tuesday, modelled the number of glaciers around the world that will completely melt at different levels of warming above pre-industrial levels.
It found that if the world warms by 2.7°C, 87 percent of New Zealand's 3300 glaciers will disappear by the end of this century.
That level of warming is a plausible scenario, according to international non-profit Climate Action Tracker, which tracks the effects of current climate change policies.
In an even more dire scenario, where global warming reaches 4°C, just 100 of the country's glaciers would remain.
A more optimistic scenario, where the world manages to limit warming to the Paris Agreement target of 1.5°C, could double the number of glaciers that still exist worldwide, the study found.
The study shows glacier loss in New Zealand peaking between 2035 and 2052, at a rate of more than 50 a year.
Globally, as many as 4000 glaciers a year could be lost by the mid-2050s,
Antarctic Research Centre associate professor Brian Anderson was not involved in the new study but has been part of long-term monitoring of New Zealand's most well-known glaciers for 25 years,
It was "quite shocking" how fast change was happening already, Anderson said.
"[One] glacier we've been studying for a long time is Brewster Glacier near Haast Pass, and particularly in the last decade, it's not just that it's continually retreating, it's breaking into parts - it's sort of falling to bits and becoming quite unlike what it used to be."
Brewster Glacier has significantly thinned and retreated since Brian Anderson began monitoring it. Photo: Claire Concannon / RNZ
Franz Josef Glacier on the West Coast - a major tourism drawcard - had retreated up the valley by more than two kilometres since he first studied it.
While many of the smaller glaciers that would disappear first were not as well-known, they were still important, Anderson said.
"They're dotted right throughout the Southern Alps, more or less, so the impact of losing them is very widespread.
"There's an insidious loss that perhaps we don't notice because it's happening piece by piece everywhere and nobody's really counting."
Canterbury University associate professor Heather Purdie has also been involved in long-term monitoring of New Zealand's glaciers and said there were widespread consequences if they were lost.
"Every glacier that's disappearing is then becoming more water in the ocean, so it has implications for cause sea level rise."
New Zealand was lucky to have plentiful water, but glaciers were still an important resource, Purdie said.
"Glaciers are these wonderful towers of frozen water sources that release water in the summer when we need it the most. There are countries that rely fully on glacier meltwater for irrigation, for water supply."
Losing glaciers completely would also change the shape and flow of rivers, as snow and rain falling at the heads of valleys would no longer be slowed by their presence.
"If you don't have snow and ice or particularly ice at the top of your catchment, the minute it rains, that water runs straight off down into like a collection lake, if you've got one, or straight down the river and out to the ocean."
Purdie has monitored Rolleston Glacier in Arthur's Pass for many years and said the pace of change had quickened in the last five to 10 years.
"You stand up there and look over it, and it's just like - wow. This thing is really thinning, it's really just shrinking before our eyes," she said.
"We've had these summers where absolutely no snow has been left on small glaciers like the Rolleston Glacier by the end of summer... The summers were just too hot, too warm, too much melt, and so your glacier is going to be going backwards really fast when it's doing a lot of melting and not getting any gain at all."
Heather Purdie, right, carries monitoring equipment up Rolleston Glacier Photo: Rasool Porhemmat
The new research made it clear that limiting warming could save thousands of glaciers around the world from that fate, she said.
"That's a frustration of working in this space, is that we're witnessing increasing temperatures, decreasing ice mass, and yet at the moment, our current government is pulling back on our pledges."
The economic argument was often used as an excuse not to take more action, Purdie said.
"People need to be able to put food on the table and pay their rent or pay their mortgages, but if we're in it for the long game and start thinking long-term, there's actually also economic implications for not doing anything."
That included the potential effects on tourism.
"Here in New Zealand glaciers are a really integral part of our recreation and tourism industries - glacier guiding, glacier hiking, mountaineering, just people even coming to view New Zealand's amazing Southern Alps and glaciers," she said.
"If it gets to the point where visitors just can't turn up and easily be able to go and see these amazing places because they've all shrunken up into the tops, the very far reaches of the mountains, then that's got economic implications too."
Trampers view Franz Josef glacier from a distance. It is no longer possible to walk up to the glacier's terminal face. Photo: ruslankphoto.com / 123RF
Even now, it was much harder to see the glaciers up close than it was a decade ago, she said.
"These things are happening and they're happening now, and we just can't afford to wait."
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