For the hundreds of millions of people who live alongside the world's coasts, the scariest sea-level rise scenario is the idea that ice sheets could collapse.
Seas are already rising rapidly, threatening to swamp cities like Miami within the lifetimes of people alive today. If the sheets of ice that sit on top of Antarctica and Greenland were to collapse, the rate of sea level rise could skyrocket, making coastal cities uninhabitable and destroying trillions of dollars of property and infrastructure.
To prevent or slow these floods from washing over cities, humanity may need to embark on the biggest civil engineering project in human history, according to a study published Thursday in the European Geosciences Union journal The Cryosphere. The project: building massive walls under the ice sheets to stop them from falling apart.
It would be a geoengineering effort — a way of reworking our planet — that might buy time for coastal areas to adapt and for humanity to reverse some of the warming we've caused by burning fossil fuels and changing the climate.
"Doing geoengineering means often considering the unthinkable," said John Moore, one of two authors of the new study and a climate scientist at Beijin Normal University and Finland's University of Lapland Arctic Centre, in a statement.
The project is still theoretical. This sort of "ice sheet intervention today would be at the edge of human capabilities," the authors wrote in the study. But it's possible that catastrophic ice sheet collapse could happen in the foreseeable future, and the processes that could trigger it at the Thwaites Glacier in West Antarctica — one of the most vulnerable glaciers — could already be happening.
"Thwaites could easily trigger a runaway [West Antarctic] ice sheet collapse that would ultimately raise global sea level by about 3 metres," Michael Wolovick, a geosciences researcher at Princeton and the other author of the study, said in a statement.
There's enough ice stacked on top of Antarctica to raise seas around the globe by almost 200 feet. While it takes time for major changes to occur with that much ice, Antarctica is melting faster than we thought, according to a study published in June in the journal Nature.
While it would take thousands of years for seas to change by hundreds of feet, people have already caused seas to start rising.