‘Extreme’ glacier loss events linked to human-caused climate change for first time
The rapidly evolving scientific field of “ extreme event event attribution ” has detected the fingerprint of human-caused climate change on a wide range of extreme weather events, including heatwaves, floods, wildfires and drought.
Now, for the first time, scientists have quantified the influence of climate change on specific episodes of extreme ice loss from glaciers.
A new study finds that human-caused climate change made the extreme “mass loss” seen in glaciers in the Southern Alps, New Zealand, in 2018 at least 10 times more likely. Another mass loss event in 2011 was made at least six times more likely by climate change.
The findings are “not surprising”, other scientists tell Carbon Brief, but the authors may have underestimated the impact of climate change on glacier retreat by focusing on individual years rather than multi-year trends.
Out of balance
Research shows that, across the world, glaciers are retreating at an accelerating rate. The ongoing global retreat of glaciers has itself been attributed , in part, to human-caused climate change.
Whether a glacier retreats or advances in the long term depends largely on changes to its “ mass balance ”. This is the annual difference between how much snow a glacier gains and how much ice it loses through surface melt, avalanches and other processes.
In a year of net mass loss, a glacier has lost more ice than it has gained. However, there is usually a time lag before this loss event translates into glacier retreat, explains Dr Lauren Vargo , a research fellow at the Antarctic Research Centre at the Victoria University of Wellington in New Zealand and lead author of the new study published in Nature Climate Change . She tells Carbon Brief:
“This can range from a few years to 100 years for different glaciers.”
Vargo’s study is the first to examine the influence of global warming on changes to a glacier’s mass balance in a single year.
The results show that human-caused climate change heightened the chances of two years of extreme glacier mass loss in New Zealand’s Southern Alps, says Vargo:
“The results of our work show that the high melt in 2011 was at least six times more likely to have happened with climate change – but could be as high as 70 times. The high melt in 2018 was at least 10 times more likely to have happened with climate change, or as high as 350 times.”
New Zealand has around 3,000 glaciers , most of which are found in the Southern Alps, a mountain range extending 500km from north to south along the South Island.
Map of the South Island of New Zealand showing glaciers. Source: Chinn et al. ( 2012 ). For the study, the researchers examined the influence of climate change on ice loss from glaciers in the Southern Alps in 2011 and 2018. These two years were chosen because they are two of the...