Will future Oz fires turn NZ snow as red as our skies?

Manaaki Whenua-Landcare Research scientist Dr John Hunt collects ash-contaminated snow at Fox Glacier following Australia's unprecedented bush fires last summer. Photo / Phil Novis

When smoke from Australia's unprecedented bush fires turned Auckland skies a ghastly orange this time last year, few likely considered the impact it was having at the other end of the country.

That was the added melting of our glaciers - coming after what had already been a horror few years for the tourist-drawing wonders.

Now, a team of scientists have set out to learn how future bush fires across the Tasman - expected to become more frequent under climate change - will worsen their decline.

"It's clear that the glaciers and snowfields of New Zealand took a large hit when so much material from the bush fires in Australia was deposited here," Manaaki Whenua Landcare researcher Dr Phil Novis said.

"But no one knows exactly how large."

A new million-dollar project, supported by the Marsden Fund, is focused on what's called albedo - a measure of the amount of solar radiation reflected back from the Earth's surface.

Because the albedo of pure snow was high, a large amount of the incoming radiation was reflected back before it could be absorbed and cause melting.

But it took surprisingly little to lessen this protective effect.

Auckland's One Tree Hill, as it appeared on January 5 last year: back-dropped by an orange sky caused by smoke from the Australian bush fires. Photo / Greg Bowker Visuals

As it happened, black carbon - created by incomplete burning of vast amounts of woody biomass, during bush fires - was one of the most effective substances at lowering albedo.

Earlier research has found it could have a dramatic impact on glaciers and snowfields - even when black carbon in fresh snow couldn't be made out by the naked eye.

In New Zealand and elsewhere, scientists suspect the the threat could be compounded naturally-occurring particles found in snow - notably snow algae.

Sometimes known as "watermelon snow", it could colour vast areas of snow red, pink or orange.

"In New Zealand they can visibly colour the glaciers on Ruapehu when viewed from the Desert Rd in summer," said Novis, who is co-leading the study with Victoria University's Dr Lynda Petherick.

"These communities also reduce the albedo of snow - and furthermore they experience positive feedback.

"They need liquid water in the snow to grow, and their growth promotes liquid water by increasing albedo and melting, and so the cycle continues. It has been said 'the last snow on Earth will be red', referring to this effect."

Glaciers like Fox Glacier have notably receded over past decades. Photo / Miles Holden

What wasn't known, was exactly how snow algae interacted with black carbon.

"Bush fire ash, for instance, is a fertiliser. On the other hand, adding it to an ecosystem can raise the pH, something to which snow algae are known to be sensitive.

"Do aerosols in snow from the bush fires promote algal growth, or hinder it? The answer could have large implications for the effect of these punctuated events on our glacial systems."

Players practised at Auckland's ASB Tennis Centre on under an orange sky on January 5, 2020. Photo / Jason Oxenham

While there had been some broad research to date, Novis said the precise interplay with ash contamination and snow biology had received little attention from scientists.

"I think it's also fair to say that the kind of snow discolouration experienced here last summer was almost unprecedented," he said.

"We initially estimated that 80 tonnes of ash had been deposited on the Fox Glacier neve for instance - and there is a lot of value in making a more accurate assessment of these quantities and their effects."

The project would draw on samples that Novis and colleagues Dr John Hunt and Dr Heather Purdie collected from glaciers in the wake of last summer's fires.

Manaaki Whenua Landcare researcher Dr Phil Novis (right) collects snow algae in Westland's Callery Valley with Professor Robin Kodner of Western Washington University in the US. Photo / Adrian Monks

"In our laboratory, I also have 20 or so strains of snow algae growing in a fridge with lights that have been accumulated during previous seasons.

"With these at our disposal we can test the effect of bush fire material on algae in some detail, using controlled growth experiments with carefully designed treatments."

The study also involved field experiments - including work at the well-studied, slowly-receding Tasman Glacier - to refine existing glacier models.

"We want to be able to add information about albedo, bush fire aerosols and algae to these kinds of models to predict their effects," Novis said.

"That's really the end goal."

While major wild fires were projected to become more common, Novis said trying to simulate exactly how that correlated with glacier melting here was tricky.

"Furthermore, much of the higher-altitude areas - roughly half the Fox neve for instance - was covered by a subsequent snowfall following aerosol deposition, which hid a lot of the discolouration, so the situation was not as bad as it could have been," he said.

"We would like to be able to develop a model that would account for all these variables and provide an accurate estimate of the effect on glacial mass balance at the end of any given season."

The new study comes as Kiwi glaciologists recently drew one of the first direct links between climate change and glacier melt - suggesting that warming made a major hit in the summer of 2018 about 10 times more likely.

It's been estimated about 30 per cent of New Zealand's ice that was catalogued in the late 1970s has been lost in the past 40 years - and the current La Nina-driven summer was likely to see more shed.

Glaciers like Fox Glacier have notably receded over past decades. Photo / Miles Holden

Novis said glaciers and snowfields remained crucial assets to New Zealand, given they formed "natural water towers" that stored then slowly released water over the dry months.

"But leaving utility aside, a peak without snow and ice has been likened to 'a clipper ship without sails', hinting at the emotion and connection people feel towards the great mountains," he said.

"There is no sign currently of our impact on them slowing down, but I think it's important to learn how substantial that impact is, and we think we can contribute to that endeavour in a significant new way."