More of the world’s coastal glaciers are melting faster than ever, but exactly what’s triggering the large-scale retreat has been difficult to determine because of natural fluctuations around the glaciers. Now, researchers at the University of Texas Institute for Geophysics (UTIG) and Georgia Tech have developed a methodology they believe will crack the code of why coastal glaciers are retreating, and conversely, how much can be attributed to human-caused climate change. Attributing a human role to coastal glaciers – which melt directly into the sea – could pave the way for better predictions of sea level rise. So far, scientists have only tested the approach on computer models using simplified glaciers. They found that even mild global warming has caused most glaciers to melt or retreat.
The next step, the researchers said, is for scientists to simulate the coastal glaciers of a real ice sheet like Greenland’s, which can hold enough ice to raise sea levels by about 22 feet (7 meters). This will reveal whether they are retreating due to climate change and help predict when the next big ice loss might occur.” The methodology we’re proposing is a road map to making confident statements about what the human role is [in glacier retreat],” said glaciologist John Christian, who is a postdoctoral researcher at the University of Texas at Austin and Georgia Tech. “These statements can then be communicated to the public and policy makers to help them make decisions.”
The methodology, published July 13 in the journal The Cryosphere, is unique because it treats the rapid retreat of glaciers as an individual probabilistic event, like a wildfire or tropical storm. For a large retreat to occur, a glacier must recede past its “threshold of stability,” which is usually a steep grade in the bedrock that helps slow its flow. The likelihood of this occurring varies with local climate and ocean conditions, which change with natural fluctuations and human-induced warming. Even small deviations can cause large changes in the behavior of a glacier, making them difficult to predict and leading to cases where glaciers were found retreating right next to those that were not.
That, said co-author and UTIG glaciologist Ginny Catania, is why the Intergovernmental Panel on Climate Change’s latest report found there is still too much uncertainty about coastal glaciers to say whether their retreat is caused by human-induced climate change or natural fluctuations climate. A new study shows how to overcome uncertainty by providing a methodology that accounts for differences between glaciers and natural climate fluctuations, while testing the influence of background trends such as global warming. According to Catania, the study means they can now attribute the mass retreat of coastal glaciers to climate change and not just natural variability.” And this is the first time anyone has done that,” she said.
To test the methodology, the team ran thousands of simulations over the past 150 years with and without global warming. The simulations showed that even moderate warming dramatically increased the likelihood of glacier retreat across the entire glacier area. When scientists created models without human-caused climate change, they found it virtually impossible for more than a few glaciers to start retreating within a few years of each other. In contrast, as of 2000, nearly all (200) of Greenland’s 225 coastal glaciers were in various states of retreat.” This study gives us a set of tools to determine the role of humans in the loss of ice from Greenland and Antarctica so we can say with confidence that it’s not just a coincidence,” said Georgia Tech glaciologist and co-author Alex Robel. Coastal glacier research builds on previous work to understand the human role in the retreat of mountain glaciers – which is now well established. The latest study was funded by UTIG and the National Science Foundation. UTIG is the research arm of UT Austin’s Jackson School of Geosciences.
Source Journal Reference: John Erich Christian, Alexander A. Robel, Ginny Catania. A probabilistic framework for quantifying the role of anthropogenic climate change in marine-terminating glacier retreats. The Cryosphere, 2022; 16 (7): 2725 DOI: 10.5194/tc-16-2725-2022
