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The West Antarctic Ice Sheet Is Retreating at a Much Higher Rate Than Previously Thought

A three-fold increase in the rate of melting has occurred since 2003 and scientists warn that global sea levels might rise by an average of four feet if the ice sheet melts completely.

by Sarah Jane Keller
Dec 4 2014, 12:15am

Image via Flickr

The world has a lot at stake in keeping the West Antarctic ice sheet from melting. Should the frozen expanse fully disintegrate, scientists say, it could raise global sea levels by an average of four feet, submerging coastal cities, like Miami, Florida.

So the findings of a new study in the journal Geophysical Research Letters are cause for great concern. The researchers found that between 1992 and 2013 the glaciers shed an average of 91.5 billion tons of water per year. That's like shedding the weight of Mt. Everest, in ice, every two years. They also learned that the rate of melt has increased three-fold since 2003.

"I think that what are we seeing is a very compelling body of evidence that things are changing very fast," Isabella Velicogna, one of the study's coauthors and a geophysicist at the University of California, Irvine, told VICE News. "The warming is not going to decrease."

The image above shows the major ice sheets of Antarctica. (Illustration by National Sea and Ice Data Center)

Historically, there's been a lot of uncertainty in measurements of Antarctic melting because the continent is so remote and difficult to study. That makes it tough to predict future ice loss, which is necessary to help coastal communities around the world prepare for sea level rise. Michael Oppenheimer, a Princeton University geoscientist who was not involved in the study, said that the new research provides important clues to how Antarctica will change in the future.

"We're particularly worried about the next 10, 20, 50, to 100 years because plans need to be put into place to defend ourselves against sea level rise, and that means we need more and more accurate projections," Oppenheimer told VICE News.

To help boost the accuracy of their research the scientists compared various techniques used to assess the rate of the Antarctic's melting, including measurements of change in the altitude of the ice packs and satellite data that detects ice loss by measuring small changes in the Earth's gravity field. Each technique confirmed the findings of the others, increasing confidence that the South Pole is indeed melting faster compared to earlier years. That's important because among the three contributors to sea level rise, which also include melting mountain glaciers and thermal expansion as the oceans warm, ice sheets are the least well understood.

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"Ten or 20 years ago, people couldn't say if Antarctica was gaining or losing mass," Ian Joughin, a University of Washington glaciologist not involved in the study, told VICE News. "Now what we really have to do is move forward and project how this will change over the next century or the next two centuries."

That remains a difficult task. Antarctica's melting is more complicated than simply dissolving an ice cube in a glass of water. Researchers are still trying to understand the complicated interactions between atmospheric temperature, ocean and wind currents, and the physics of the ice packs. For example, a current of warm water is eating away at one of West Antarctica's major ice shelves and that seems to create a positive feedback loop that leads to even more melting as glaciers become free to flow into the ocean. It's also not clear how long the warm ocean current will stick around, or how much global warming is contributing to its presence and persistence.

Even if the warm current diminishes it's likely to buy only a little bit of geologic time for West Antarctica's ice, according Joughin. "When we modeled it, we showed that the retreat has already started and, while the rate of retreat will be controlled by the temperature of the water, it looks like it may be ongoing no matter what," he said. "So if the temperature goes back down, it may take 900 years for the glacier to retreat. But if it stays warm, it could be as little as a couple of hundred years."

For now, Velicogna points out that their observations show more severe melting than what models, such as those used by the UN Intergovernmental Panel on Climate Change, predict.

"If we keep going at this pace," she told VICE News, "we're not set up for a very rosy 2100."

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Follow Sarah Jane Keller on Twitter: @sjanekeller

Image via Flickr