Sea level rise projections are complicated and difficult to calculate. This is largely because the potential collapse of the Antarctic ice sheet remains the “largest single source of uncertainty” for scientists working to understand future sea level rise, according to a new study which seeks to change that.
In a study released July 8 in the Proceedings of the National Academy of Sciences (PNAS), scientists have developed a more accurate way to better understand what they call “marine ice sheet instability.” This term refers to situations in which an ice melt feedback loop is created — a potential “rapid and irreversible retreat” of the continent’s ice that occurs wherever the land underneath the glaciers deepens, or slopes, towards the interior of the the ice sheet.
As the grounding line — “a critical boundary where ice flowing from the ice sheet interior becomes thin enough to float in ocean water” — shifts further back inland, the more the ice is likely to melt, which then further shifts the grounding line, and subsequent melting.
Melting sea ice doesn’t contribute to sea level rise. The same can not be said for land ice — the more it melts, the potential for significant sea level rise increases right along with it. According to the study, while the range of future sea level rise projections vary widely due to the uncertainty in projections surrounding the melting of Antarctica’s glaciers, as ice sheets become more unstable with rising temperatures, sea level rise “may accelerate significantly.”
The new mathematical model developed by the researchers shows that “marine ice sheet instability greatly amplifies and skews uncertainty in sea-level projections with worst-case scenarios of rapid sea-level rise being more likely than best-case scenarios of slower sea-level rise.”
“Antarctica is an ice leviathan,” a press release for the study describes. There is almost eight times as much ice in the Antarctic ice sheet as there is in the Greenland ice sheet. And according to the National Science Foundation, over the last six years, five Antarctic glaciers have doubled their rate of ice loss.
This includes the now-famous Thwaites Glacier — a massive expanse of ice that scientists fear could trigger dramatic sea level rise. If the glacier reaches a tipping point, the study stays, it could lose all of its ice in just 150 years. This would trigger sea level rise of about half a meter, or 1.64 feet. For context, current sea level rise is nearly 8 inches (20cm) above pre-global warming levels — and communities around the world are already experiencing the impacts of coastal flooding as a result.
Moreover, scientists warn that the instability would not stop even if at some point global warming were to end and temperatures stopped rising. Antarctica’s glaciers would keep sliding into the sea and continue accelerating sea level rise over the coming centuries.
“If you trigger this instability, you don’t need to continue to force the ice sheet by cranking up temperatures. It will keep going by itself, and that’s the worry,” Alex Robel, assistant professor in Georgia Tech’s School of Earth and Atmospheric Sciences and the study’s lead author said in a statement, adding that “Climate variations will still be important after that tipping point because they will determine how fast the ice will move.”