West Antarctic ice melt poses unique threat to U.S.

Background: The reason the location of the ice melt is important is due to peculiarities of the Earth's climate system that have long been understood in academia, but not well-known by the public.

• The U.S. would see far more sea level rise from the melting of West Antarctica when compared to the shedding of ice from the Greenland Ice Sheet. For example, for every 1 centimeter of sea level rise from West Antarctica, Boston would see an increase in local sea level of about 1.25 centimeters.

The science: The reason for the 25% sea level rise tax centers on gravity.

• Rob DeConto, a climate scientist at the University of Massachusetts, says that as ice sheets melt, there's an elastic response from the Earth. "The Earth’s gravitational field changes because we’re redistributing mass around the planet,” he tells Axios.
• When an ice sheet loses ice, it reduces its gravitational pull toward itself, which means the local sea level near the ice sheet — be it Greenland or Antarctica —is reduced.
• Even if the entire Greenland Ice Sheet were to melt, places close to Greenland, such as northern Europe and northeastern North America, "wouldn't even know," DeConto says. “If you’re close to the ice sheet thats losing mass you don’t really feel the effects as much.”
• It's the distant places that compensate for this loss in mass. “It’s totally flipped upside down for Antarctica," he says, as there is a "broad bullseye" around North America. “Sea level rise for the future, it’s not happening at the same rate in every part of the world… this gravity thing has a big impact,” DeConto says.

In addition, the loss of mass in Antarctica has a small change in the Earth's axis of rotation, which can also help to distribute sea level rise unequally.

• De Conto and other researchers told Axios that projections in studies published Wednesday don't present a true worst-case scenario for Antarctic ice melt.

Worst-case scenario? The new research also presents a possible scenario for Antarctic ice melt through 2070:

• In this, greenhouse gas emissions continue virtually unabated. This leads to global average surface temperatures rising to 3.5 degrees Celsius, or 6.3 degrees Fahrenheit, above the preindustrial average, and many of the most important ice shelves that hold back the West Antarctic Ice Sheet would be lost.
• The rate of sea level rise would also increase to 5 mm per year, with economic losses from the flooding of coastal cities projected to exceed $1 trillion per year.

This sounds quite serious, and it is, but as Penn State University climate scientist Richard Alley said, it's not even the worst-case scenario. Rather, it's closer to a most likely scenario, based on recent emissions trends, Alley says.

"Considering sea level rise, for example, the future rise could be a little smaller or a little larger, or a lot larger — there is a "long tail" on the "bad" side," Alley says.

A decade to act: DeConto, for his part, said although the Antarctic melt rate is accelerating, there's still time to slow things down and ensure a less damaging future.

"I think there’s still a lot of room for optimism, that we can have a really big impact on the outcome for sea level rise," DeConto says. “It’s not like it’s completely too late and there’s nothing we can do about it. That’s not true.”

Helen Amanda Fricker, a researcher at the Scripps Institution of Oceanography, echoed this point and gave a more specific timetable:

"The next few years will be a pivotal period for decision making with regard to Antarctica. As we observe the system for longer, we see more and more changes of the type we feared could happen as the climate warms. Depending on what is decided, we could be looking at significant and irreversible changes over the next 50 years."

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