Sea water reaching the doorstep of a housing development in Charleston, South Carolina. AP Photo/Stephen B. Morton

New research doubles previous predictions if greenhouse gas emissions go unchecked.

Sea level rise can be difficult to imagine concretely. It’s often discussed as a gradual phenomenon, a threat whose effects will only really be felt by far-distant generations.

But new research has made it impossible to continue in this line of thought. In an article published recently in the journal Nature, the scientists Robert DeConto and David Pollard double the prediction for sea level rise expected by the year 2100 from three feet to six feet, if the current rate of greenhouse gas emissions holds steady. By the year 2500, it could hit 50 feet.

To demonstrate how, exactly, these numbers translate to reality, Climate Central created sliding data visualizations of possible realities for Miami, Boston, and Charleston in 2100 (see the map of the whole U.S. here). In one future, where pollution is drastically cut over the next 85-odd years, water levels will have risen only two feet, leaving the surface areas in these places mostly intact. In the other, however, where emissions go unchecked, the maps are splattered with blue, showing the extent to which rising sea levels will waterlog land along the coasts.

Fast Company notes the potential implications for these coastal locales:

By the end of the century, if greenhouse gas emissions continue unchecked, Fenway Park, along with a huge chunk of the rest of Boston, could end up underwater. Miami Beach might be submerged. The same is true for parts of every coastal city, from Hong Kong to Mumbai.

This new estimate is higher because it accounts for the disintegration of the Antarctic ice sheet. This phenomenon occurred around three million years ago, when the planet was undergoing similarly warm temperatures, and is repeating now.

Pollard and DeConto used computer modeling to track how surface melt flowing into pre-existing cracks causes ice sheets to break away from the continent. In turn, this process exposes very tall, unsupported ice cliffs, which subsequently disintegrate and fall into the ocean, causing the water levels to rise. Once the researchers determined how the fracturing of the Antarctic ice sheet precipitated the increase millennia ago, they were able to apply the model to the planet today.

These processes have already begun to destabilize parts of Greenland, Pollard says, but impact from Antarctica, given its vastness, is what determined the scientists’ final predictions.

The previous estimate from the International Panel on Climate Change was put forth in 2013, and included very little data from Antarctica on predicted sea level rise for this century—in total, its contribution was estimated at just a few centimeters, Pollard says. The 2013 report, which estimated only a three-foot rise by 2100, cited glacial melting and the gradual expansion of ocean water as the main causes. The new modeling system—and its markedly higher estimate—add fresh sense of immediacy.

These findings are especially crucial now, Pollard says, because some of the consequences are preventable. The precipitous rise, he adds, occurs in their model “only if business continues as usual, and the CO2 levels keep going up.” But if warming is limited to the levels recommended in the Paris Agreement—well below 2°C (3.6°F)—the model shows a much less drastic increase.

Rather than viewing their prediction as a final word or an inevitability, Pollard hopes it acts as a motivating force for more scientists to get involved—and for climate change recommendations to be implemented sooner rather than later.

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