More of the world’s coastal glaciers are melting faster than ever, but pinpointing exactly what is causing the large-scale retreat has been difficult due to natural fluctuations in the surrounding glaciers. Now researchers at the University of Texas Institute for Geophysics (UTIG) and Georgia Tech have developed a methodology that they believe cracks the code for why coastal glaciers are retreating and, in turn, how much can be attributed to climate change. caused by man. Attributing the human role to coastal glaciers, which melt directly into the sea, could pave the way for better predictions of sea level rise.
Until now, scientists have tested the approach only on computer models using simplified glaciers. They found that even moderate global warming 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 contains enough ice to raise sea levels about 7 meters (22 feet). That will reveal whether they are retreating due to climate change and help predict when the next major ice loss might occur.
“The methodology we are proposing is a roadmap for making confident claims about what the human role is [in glacial retreats]said glaciologist John Christian, a postdoctoral researcher at the University of Texas at Austin and Georgia Tech. “Those statements can then be communicated to the public and policymakers, and help them make decisions.”
Published on July 13 in the magazine cryosphere, the methodology is unique in that it treats rapid glacier retreat as a single probabilistic event, such as a wildfire or tropical storm. For a major retreat to occur, the glacier must retreat beyond its “stability threshold”, which is usually a sharp rise in the underlying bedrock that helps slow its flow. The likelihood of that happening varies depending on local weather and ocean conditions that change with natural fluctuations and human-caused warming. Even small variations can cause large changes in the behavior of a glacier, making them difficult to predict and leading to cases where glaciers were found to be receding right next to others that were not.
That, said co-author and UTIG glaciologist Ginny Catania, is why the latest Intergovernmental Panel on Climate Change report found there was still too much uncertainty about coastal glaciers to say whether their retreat is due to climate change caused by man or natural climatic fluctuations.
The new study shows how to overcome uncertainty by providing a methodology that takes into account differences between glaciers and natural climate fluctuations, while testing the effect of background trends such as global warming. According to Catania, the study means they can now attribute the massive retreat of coastal glaciers to climate change and not just natural variability.
“And that’s the first time anyone has done that,” he said.
To test the methodology, the team ran thousands of simulations of the last 150 years with and without global warming. The simulations showed that even modest warming dramatically increased the probability of glacial retreat across the ice sheet.
When scientists ran models without human-caused climate change, they found that it was virtually impossible for more than a few glaciers to start retreating years apart.
In contrast, since 2000, nearly all (200) of Greenland’s 225 coastal glaciers have been in various states of retreat.
“This study gives us a toolbox for determining the role of humans in Greenland and Antarctic ice loss, to say with confidence that it’s not just a coincidence,” said Georgia Tech glaciologist and co-author Alex Robel. .
Research on coastal glaciers builds on earlier work to understand the human role in mountain glacier retreat, which is now well established. The latest study was funded by UTIG and the National Science Foundation. UTIG is a research arm of the UT Austin Jackson School of Geosciences.
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