Collapse of West Antarctic Ice Sheet May Be Worse Than Scientists Predicted

It has been a long-cited statistic that the West Antarctic Ice Sheet contains enough ice to contribute around 10.8 feet to global sea-level rise.

Now, a new study has found that it could raise water levels even higher than that—by as much as 3.2 feet or 30%—all because of a geological process that had previously been discounted.

“The magnitude of the effect shocked us,” study co-author and Harvard Department of Earth and Planetary Sciences Ph.D. student Linda Pan said in a press release.

The study, published in Science Advances late last month, focused on how the behavior of the bedrock beneath the West Antarctic Ice Sheet (WAIS) would impact its contribution to sea-level rise. 

“WAIS is grounded below sea level—if the ice sheet were not there, the area would be covered by ocean,” Pan explains to Treehugger. “So, when WAIS melts, ocean water will flow into the region where the ice sheet previously was.”

However, the ice is also sitting on top of bedrock that is compressed by the pressure of the ice. As the ice melts, the bedrock rises through a process called "uplift," meaning there is less space for the ocean water that the ice has become. 

“Thus, this uplift pushes water out of the marine sectors and into the open ocean, which increases global mean sea level,” Pan explains. 

Pan refers to this displacement as a “water outflux mechanism.” Previous studies had considered this mechanism and determined its contributions to sea-level rise would be minimal and occur over a long period of time. 

However, there is evidence the rocky mantle below the WAIS is low viscosity, meaning it flows more easily. Pan and her team were aware of this evidence because they are trained geophysicists. 

“Our experience in both these aspects have put us in a unique position to put these two together for the first time in an interdisciplinary sense,” Pan tells Treehugger. 

By incorporating both the water outflux mechanism and the low viscosity mantle into models, they were able to show the WAIS’s contribution to sea-level rise would be greater than previously believed.  

In fact, it could contribute 30% more than previously thought over 1,000 years from its collapse, their models found. And the changes weren’t only gradual. One model found it could contribute an extra 20% to global sea-level rise by the end of the current century because of the water outflux mechanism.

“Every published projection of sea-level rise due to melting of the West Antarctic Ice Sheet that has been based on climate modeling, whether the projection extends to the end of this century or longer into the future, is going to have to be revised upward because of their work,” Jerry X. Mitrovica, the Frank B. Baird Jr. Professor of Science Harvard’s Department of Earth and Planetary Sciences and a senior author on the paper, said in the press release. “Every single one.”

The study is an example of how much we don’t yet know about the impacts of the climate crisis, and how many unrelated mechanisms can interact with warming temperatures to wreak havoc. 

“Science is full of surprises,” Pan tells Treehugger. 

To better understand all the factors determining how the West Antarctic Ice Sheet might collapse, she says more field research and satellite measurements would be needed to back up the models.

The study is also further evidence that the impacts of anthropogenic climate change will persist even if world leaders act immediately to stop burning fossil fuels. While an extra 3.2 feet of sea-level rise over 1,000 years might not sound like much, more than 150 million people currently live within that distance of the seashore. The previously predicted 10 feet of sea-level rise would be enough to sink both New York City and Miami. 

“[O]ur work shows that the damage that we are doing to coastlines will continue for centuries, even if the melting of the ice sheet were to cease,” Pan tells Treehugger. 

Now that this study is complete, Pan and her team will continue to study these potential damages. 

“Our group focuses on regional sea level changes throughout recent and ancient history, as well as into the future,” Pan explains. “The ocean is not a bathtub in which water rises uniformly, and taking that into account is important for both elucidating enigmatic climatic periods in Earth history and for understanding the risks that coastal communities face in our progressively warming world.”