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Glaciers in trouble after marine heatwave

From Our Changing World, 11:51 am today
Alison Ballance, Senior Producer @alisonballance

New Zealand’s glaciers are feeling the heat.

Climate scientists and glaciologists from NIWA and Victoria University of Wellington have just completed their annual end of summer snowline flight over nearly 50 glaciers in the Southern Alps.

They report that the summer’s marine heatwave has left the ice giants in “sad shape”.

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Glaciers in the Southern Alps are showing signs of decline following a record hot summer. On 30 of the 50 glaciers surveyed, no snow survived the summer. Photo: Dave Allen / NIWA

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Glaciers play a vital role in the world’s hydrological cycle. In New Zealand’s Southern Alps, they are mountain ‘water towers’, whose melt water drip-feeds into streams and rivers across Canterbury and Westland.

But glaciers are also sensitive barometers of a changing climate, and around the world they are melting and retreating.

Glaciers react remarkably quickly to variations in snowfall and temperature, and changes in the quantity of ice they hold could have profound consequences on the amount of water that flows from the Southern Alps each year.

Scientists took to the air in two fixed wing planes to photograph glaciers for the end of summer snowline survey. Photo: Dave Allen / NIWA

Measuring the glaciers

In the late 1970s, glaciologist Dr Trevor Chinn carried out an inventory of all of New Zealand’s glaciers. He counted more than 3200.

Trevor chose 50 representative glaciers, and beginning 40 years ago started to measure the annual snowline as a proxy for glacier health.

The snowline is the demarcation where there is snow from the previous winter above and exposed bare ice below.

The snowline survey happens in March each year, just before the first autumn snowfalls begin to obscure it. The scientists take to the air in small fixed-wing planes and capture aerial photographs of each index glacier that can be analysed and compared to photos from previous years.

Brian Anderson photographs a glacier during the 2018 end of summer snowline survey. Photo: Dave / Allen NIWA

“We look at the snowline and estimate the volume change for these index glaciers”, says climate scientist Dr Andrew Lorrey, from NIWA. From this, he can calculate exactly how much ice is in the Southern Alps, and whether the amount is growing or shrinking.

“From year to year, our climate varies,” says Dr Lorrey. “One of the reasons we are doing this is to look at how climate variability and long term climate change affect the snow and ice resources of New Zealand.”

Very little snow recorded this year

This year’s survey results were sobering.

Thirty of the 50 glaciers had snowlines that were above the tops of the mountains, which means than none of last year’s snowfall had survived.

Instead of a fresh blanket of snow from last winter, what the team saw was ice and dirty snow from previous years.

Last year, just 16 of the glaciers had lost all their annual snow.

“Simply put, they are looking in pretty sad shape this year. You can definitely tell there are some impacts from the ... record warm temperatures this summer,” says Andrew.

With no snow remaining from last winter, many New Zealand glaciers are showing old ice and dirty snow from previous years. Photo: Dave Allen / NIWA

New Zealand’s record-breaking summer saw a marine heatwave in the Tasman Sea, with temperatures up to six degrees Celsius above average.

The snowline observations confirm previous research by NIWA and Victoria University of Wellington, which shows a strong connection between sea surface temperatures in the Tasman Sea and temperatures in the Southern Alps.

It is not as simple as the warm weather just melting a glacier’s ice. What the warm temperatures do is “reduce the potential for any of the snow that fell in the previous winter period to be retained through summer and into next year,” says Andrew.

The end of summer snow line survey involved scientists from NIWA, Victoria University and Alpine and Polar Processes Consultancy. Left to right - Huw Horgan, Brian Anderson, Lauren Vargo, Andrew Lorrey, Andy Woods and Trevor Chinn. Photo: Dave Allen / NIWA

The importance of snow

Snow is the crucial ingredient in a glacier. Over time, snow accumulates and gradually compresses into ice, and a glacier begins to build when the rate of accumulation is greater than the rate of melting.

Andrew likens it to saving money in a piggy bank; “there have to be some reserves in the piggybank from year-to-year and you have to build up those savings.”

“A year like this is incredibly detrimental for our glaciers, and for our snow and ice,” says Andrew.

He says he is worried about the future of our glaciers, and notes that what will be important is the interplay between natural climate variation, and warming from human-induced climate change.

Andrew says that the water stored in glaciers is a vital resource in many ways – it is important for the ecology of both the mountains and the lowlands, it supports agriculture, and provides hydro-electricity that powers homes and businesses across New Zealand.

If the ‘water towers’ in the Southern Alps vanish, we will have to face the harsh reality of life in a much drier country.

Glaciers on Our Changing World

Brian Anderson and Andrew Mackintosh discuss the past and the future of New Zealand’s glaciers.

Sediment cores in Lake Ohau reveal the 18,000 year old glacial history of the Southern Alps.

Franz Josef and Fox glaciers briefly buck the worldwide trend of retreating glaciers.

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