Researchers at the University of Texas Institute for Geophysics (UTIG) and Georgia Tech have developed a method they hope will crack the code of why coastal glaciers are retreating and how much of that is due to human-caused climate change. Attributing a human role to coastal glaciers — which melt directly into the ocean — paves the way for better predictions of sea-level rise.
The study was published in The Cryosphere Journal. So far, scientists have only tested the approach on computer models using simplified glaciers. They found that even modest global warming is causing many 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, which has enough ice to raise sea level by about 22 feet (7 meters). That could reveal whether they’re retreating due to climate change and help predict when the next big ice loss will occur.
“The methodology we propose is a road map for making confident statements about human character [in glacial retreats]” said glaciologist John Christian, a postdoctoral researcher at both the University of Texas at Austin and Georgia Tech.
“Those statements will inform the public and policymakers and help them in their decision making.” This methodology is unique because it treats rapid glacier retreat as an individual potential event, like a wildfire or tropical storm.
For a major retreat to occur, the glacier must retreat beyond its “stability threshold,” which is usually a steep rise on the underlying rock that helps slow its flow. The likelihood of that happening varies depending on local climate and ocean conditions that change with natural fluctuations and human-caused warming.
Even small variations can cause large changes in a glacier’s behavior, making them difficult to predict and leading to instances of glaciers retreating next to non-glaciers.
Co-author and UTIG glaciologist Ginny Catania said the final Intergovernmental Panel on Climate Change report found there is still much uncertainty about coastal glaciers, whether their retreat is due to human-caused climate change or natural climate fluctuations.
A new study shows how to overcome uncertainty by providing a methodology that accounts for differences between glaciers and natural climate fluctuations when testing the impact of background trends such as global warming.
According to Catania, the study means they can now attribute mass coastal glacier retreat 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 modest warming dramatically increased the probability of ice sheet-wide glacier retreat. When scientists ran models without human-caused climate change, they found that it was virtually impossible for glaciers to begin retreating more than a few years apart.
In contrast, since 2000, nearly all (200) of Greenland’s 225 coastal glaciers are in various states of retreat. “This study gives us the toolbox to identify the role of humans in the loss of ice from Greenland and Antarctica, to say with confidence that it’s not just a coincidence,” said Georgia Tech glaciologist and co-author Alex Robel.