Extreme glacier melt is due to human greenhouse emissions, study finds

Brewster Glacier in New Zealand photographed during the 2020 End of Summer Snowline Survey. The glacier has been stripped of nearly all snow, leaving only bare, blue-coloured ice. Such glaciers are not sustainable in a warming climate. Photo Credit: Dr Lauren Vargo.

An international study involving a Monash climate scientist has revealed a strong link between human greenhouse gas emissions and the increased melting of glaciers.

The study, published today in Nature Climate Change, is only the second to directly and formally link increased glacier melt to climate change.

Professor Andrew Mackintosh, Head of the Monash University School of Earth, Atmosphere and Environment, was one of the study authors, which was led by his former PhD student Dr Lauren Vargo, from the Antarctic Research Centre at Victoria University Wellington. The Antarctic Research Centre, formerly led by Professor Mackintosh, was recently awarded the 2019 New Zealand Prime Minister’s Science Prize.

Glaciers on Earth have retreated rapidly during the last few decades, and they are one of the largest sources of modern sea level rise. Shrinking glaciers also put water resources at risk in many communities around the world.

“In recent times we have observed that in certain years we experience extreme levels of glacier melt,” Professor Mackintosh said.

“During these years, the entire snowpack from the previous winter - and many previous years - is stripped away from glaciers, leaving them bare and accelerating their demise,” he said.

“Dr Vargo and our team have now shown that these extreme glacier melt events are directly linked to human climate change.

If climate warming continues at the current rate, extreme melting events will become even more common, leading to a bleak future for glaciers.”

Dr Vargo’s study focused on a group of glaciers in New Zealand’s South Island.

“Our results show that high levels of melt in 2011 were six times more likely to have happened due to climate change, and high levels of melt in 2018 were at least 10 times more likely to have happened due to climate change,” Dr Vargo said.

“These increases in likelihood are due to temperatures that are 1 degree Celsius above pre-industrial levels, confirming a connection between greenhouse gas emissions and high annual ice loss.”

This study began in response to observations made during the 2018 End of Summer Snowline Survey. The annual survey led by Dr Andrew Lorrey at the National Institute of Water and Atmospheric Research (NIWA) in New Zealand, records the snowline position on New Zealand’s glaciers and ice geometry (thickness and flow) changes using aerial photos, which then allowed Dr Vargo to determine the amount of growth or shrinkage of key glaciers.

In 2018, the Survey team observed the least amount of snow on the glaciers since the Survey began. Researchers wanted to determine to what extent this lack of snow was due to human influence.

“We used a method called extreme event attribution, which has previously been used by co-author Dr Andrew King at the University of Melbourne to calculate the human influence on extreme climate events like heatwaves and droughts,” Dr Vargo said. “To get these results, we developed a framework that uses extreme event attribution together with calculating glacier mass changes with computer models.”

“Our results show that extreme glacier melting events are due to the greenhouse gases emitted by humans. Whether this continues is up to us. It is only by reducing our emissions that the most extreme glacier melt in the future can be avoided” says Professor Mackintosh.

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