It is “very likely” that the increased melting of 10 glaciers in New Zealand’s South Island is caused by human greenhouse gas emissions, a new study has found.
Specifically, the researchers say, results show that high levels of melt were six times more likely to have happened due to climate change than other processes in 2011, and at least 10 times more likely in 2018.
“These increases in likelihood are due to temperatures that are one degree Celsius above pre-industrial levels, confirming a connection between greenhouse gas emissions and high annual ice loss,” says lead author Lauren Vargo, from the Antarctic Research Centre at NZ’s Victoria University of Wellington.
Published in the journal Nature Climate Change, the study also involved other researchers from the ARC and NZ’s National Institute of Water and Atmospheric Science, as well as Monash University and the University of Melbourne in Australia.
It is, they say, only the second to directly and formally link glacier melt to climate change.
The impetus was NZ’s annual End of Summer Snowline Survey, which records the snowline position on glaciers and changes in ice geometry (thickness and flow) using aerial photos.
In 2018, Vargo and colleagues observed the lowest amount of snow on the glaciers since the survey began and wanted to determine to what extent this was due to human influence.
“We used a method called extreme event attribution, which is used to calculate the human influence on extreme climate events like heatwaves and droughts,” she says.
“To get these results, we developed a framework that uses extreme event attribution together with calculating glacier mass changes with computer models.
“For example, the extreme loss of mass we saw of one glacier – the Rolleston Glacier – in 2011 would be a 1-in-100-year event under natural conditions, but due to climate change this has become a 1-in-8-year event.
The method can now be used to study glaciers elsewhere, the researchers say.
“There are over 100 glaciers globally that have annual measurements of mass change available, so we can use these with our new method to calculate the human fingerprint on glacier melt around the world,” Vargo says.
“We know that many glaciers globally experienced their highest levels of melt in the last decade, so we look forward to investigating the link between this melt and human climate influence.
“Ultimately we hope this research can contribute to evidence-based decision making on climate change.”