By Becky Sicking

According to a recent study published in the journal Nature, the Amundsen Sea off of western Antarctica is rising, slowly but steadily. No one lives there. No country has bothered to claim the land near the sea. However, scientists are looking hard at recent apparent ice loss there. At one time, scientists thought ice shelves were relatively stable. The cold waters off of Antarctica slow their melting, and land features such as islands slow their advance into the sea.

Ice shelves are floating sheets of ice that connect to a glacier resting on a land mass. Most of the ice shelves on Earth are located around Antarctica, although there are some in the Northern Hemisphere as well. The ice shelves are formed when glaciers and ice streams push ice into the sea. This body of ice floats on a layer of seawater, still connected to the glaciers that feed it. The already extremely cold water slows the melting of the floating ice. Over time, the ice sheet grows and expands as glacier ice continues to flow into the sea. When ice sheets are in protected areas along coasts, they can survive for thousands of years.

The shelves slowly move into the ocean as they float. Their movement goes even slower as they scrape across land features such as islands and peninsulas. The bits of land also help hold up the weight of the shelves. As the ice shelves slow, they force the glaciers behind them to move slower too. Now, however, scientists find that warming ocean waters are melting the bottoms of the ice shelves more quickly. In some places the warmer ocean water has also melted underneath the glaciers. This makes the connection between the glacier and the shelf weak. When this happens it causes the ice sheets to crack and break off, or calve, and the result is icebergs.

Scientists are concerned because if the ice shelves collapse, their function as a plug in front of the glacier will be gone. Then the glacier ice will flow faster into the warmer water, where it will melt more quickly. As a result, the seas will rise even faster. More water in the world’s oceans from glacial melting will eventually cause flooding along all coasts—even those far from Antarctica.

The recent Nature article was authored by Robert DeConto of the University of Massachusetts Amherst and David Pollard of Pennsylvania State University. They warn that ice shelves in the western Antarctica may already be vulnerable to an unstoppable collapse. The data suggests that by 2100 the sea level could rise by 1 meter (more than 3 feet) and by 2500 the level could be 15 meters higher than today.

DeConto said, "We're looking at the potential for a rate of sea level rise that we will be measuring in centimeters (rather than milliliters) per year—literally an order of magnitude faster. . . . Can we build walls and levies and dikes fast enough to keep up with that? One concern would be that at that point you're sort of looking at managed retreat essentially, rather than geoengineering in a lot of places. At the high end, the worst-case scenarios, with sort of business as usual greenhouse gas emissions . . . we will literally be remapping coastlines. North America is kind of a bull's eye for impacts of sea level rise if it's the west Antarctic part of Antarctica that loses the ice first ... That's the place that we're worried about losing ice first."

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