Many scientists are contributing to the growing body of research that predicts rising sea levels in the future.

In a sea of climate change studies, however, it is not impossible to find a set of statistics that may oppose another.

Such is the findings of a pair of climate scientists from the United States, who suggest that an accurate prediction of rising sea levels is actually double that of the most recent estimates.

In fact, the two researchers say previous climate models underestimated the potential sea level rise over the next 100 years, as well as the melting of the Antarctic ice sheet. They believe accurate estimates could spell disaster for low-lying cities.

Looking Into The Past

Carbon dioxide emissions during the Eemian and Pliocene era are an analog for today's levels, but sea levels at that time were higher than today.

Robert DeConto and David Pollard - climate scientists from the University of Massachusetts Amherst and Pennsylvania State University, respectively - used a three-dimensional ice sheet model to reconstruct the Earth as it looked during the Pliocene 3 million years ago.

They also simulated conditions during the Eemian era, only about 125,000 years in the past. Sea levels at both periods were about 20 feet to 30 feet higher than today, researchers find.

DeConto says the melting of the Greenland ice sheet can only explain a portion of the phenomenon during the Eemian and Pliocene, and that most of it must have been the result of retreat on Antarctica.

The Antarctic ice sheet will melt faster than previous estimates, and will mirror the melt rates from the Pliocene and Eemian era, the researchers say.

How so? Apparently, current predictions fail to include hydro-fracturing, a process in which meltwater on ice shelves force big chunks of ice to break off and fall into water. With hydro-fracturing, Antarctica can potentially contribute greater than a meter (39 inches) of sea level rise by 2100 if emissions continue, researchers warn.

"We are not saying this is definitely going to happen, but I think we are pointing out that there's a danger, and it should receive a lot more attention," Pollard told The New York Times.

Opposing Findings

Meanwhile, estimates from the International Panel on Climate Change (IPCC) say that a 0.5-meter rise over sea levels in 1990 will occur by 2100.

"Global sea level is projected to rise during the 21st century at a greater rate than during 1961 to 2003," the IPCC report suggests, saying that the rate will be at 4 millimeters (0.15 inches) per year.

The National Oceanic and Atmospheric Administration (NOAA) concluded in 2013 that sea level rise around the globe will rise no more and no less than 0.2 to 2 meters (0.6 feet to 6.5 feet) by 2100.

The agency refers to its "intermediate-low scenario" based on projected ocean warming of a 1.6 foot rise, which in itself is no small obstacle. A previous study revealed that this estimate alone could displace 13.1 million Americans in coastal cities.

"This could spell disaster for many low-lying cities. For example, Boston could see more than 1.5 meters [about 5 feet] of sea-level rise in the next 100 years," says DeConto. "But the good news is that an aggressive reduction in emissions will limit the risk of major Antarctic ice sheet retreat."

A Real Possibility

Pollard and DeConto, however, say that the NOAA's prediction of a 5- to 6-foot rise is a possibility that should not be shrugged off.

Eric Rignot of the University of California, Irvine, who was not involved in the study, agrees.

"People should not look at this as a futuristic scenario of things that may or may not happen. They should look at it as the tragic story we are following right now," says Rignot. "We are not there yet ... [But] with the current rate of emissions, we are heading that way."

DeConto and Pollard's findings are published in the journal Nature.

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