The melting of the Greenland ice sheet could eventually raise global sea levels by at least 10 inches even if humans immediately stop burning the fossil fuels that are warming the planet to dangerous levels, according to a new study published on Monday.
The study, published in Nature Climate Change, focuses on what researchers call “committed” sea-level rise, a measure that takes into account the warming that has already occurred.
That approach differs from most earlier research, which has been based on computer modeling and has generally predicted much lower losses of ice from the Greenland ice sheet. The latest assessment from the United Nations Intergovernmental Panel on Climate Change, for example, projects somewhere between two and five inches of sea-level rise by 2100.
The 10-inch increase forecast in the new study, which does not give a timeline, could be much higher if temperatures continue to rise, as they almost certainly will, said Jason Box, a glaciologist at the Geological Survey of Denmark and Greenland who was the paper’s lead author.
Dr. Box said computer modeling typically used by glaciologists so far was “not up to the task” of representing how rapidly ice sheets are melting. His team’s research instead studied satellite measurements taken between 2000 and 2019.
In the new study, researchers examined what’s known as the climactic snow line, or the boundary between a snow-covered and snow-free surface, on the ice sheet.
The line fluctuates every year in response to cooler or warmer temperatures, and when one area grows larger than the other, the ice sheet moves away from “equilibrium.” In a high-melt year, the snow line is pushed farther up the ice sheet, which means the area that accumulates snow is smaller, resulting in a smaller ice sheet.
The major issue with the new study is the lack of a time horizon attached to the predictions, said Sophie Nowicki, an ice sheet expert in the University at Buffalo’s geology department who was not involved in the research. Do you get that number by 2100, she wrote in an email, “or in thousands and thousands of years?”
A good analogy for the study, she wrote, is the typical growth and weight charts you might see when you take your children to the doctor for a checkup. The charts give you an indication of how tall your child may possibly become, but they are not good at predicting a growth spurt or the precise timing of the growth.
The approach is “more grounded in what has already happened” than past ice sheet modeling, and it takes us beyond what has already been done before, said John Walsh, chief scientist at the University of Alaska Fairbanks, who was not involved with the study.
The conclusions indicate that even the most conservative estimate of melting ice could have dangerous human effects, Dr. Walsh said. While 10 inches may not seem like much on average, the sea level does not rise equally everywhere. Some regions, especially lower-lying coastal areas, could be hit with disproportionately devastating flooding.