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Many climate scientists have predicted sea-level rise over the next century as a result of manmade climate change. But in a new study, a pair of climate scientists say an accurate estimate of sea-level rise is actually double that of previous predictions.

In a study published Wednesday in the journal Nature, Robert DeConto at the University of Massachusetts Amherst and David Pollard at Pennsylvania State University say previous ice-sheet-climate models 鈥渦nder-appreciated鈥� the melting of the Antarctic ice sheet.

But to better understand the future, and Antarctica鈥檚 potential role in it, Professor DeConto and Professor Pollard first looked to the past.

Using a three-dimensional ice sheet model, DeConto and Pollard reconstructed the Earth as it looked 3 million years ago during the Pliocene era and then 125,000 years ago during the Eemian era. During the Pliocene and Eemian, atmospheric carbon dioxide emissions were comparable to today鈥檚 levels, but sea levels were between 20 to 30 feet higher than they are today.

鈥淪o at a time in the past when global average temperatures were only slightly warmer than today, ,鈥� DeConto says in a press release. 鈥淢elting of the smaller Greenland Ice Sheet can only explain a fraction of this sea-level rise, most which must have been caused by retreat on Antarctica.鈥澛�

DeConto and Pollard say Antarctic ice will melt faster than scientists previously thought, instead mirroring the melt rates from 125,000 and 3 million years ago. Current sea level rise predictions fail to account for 鈥渉ydro fracturing,鈥� say DeConto and Pollard, a process where meltwater on ice shelves causes big chunks of ice to crack off and fall into the water. And with the collapse of these vertical cliffs, "Antarctica has the potential to of sea-level rise by the year 2100" if atmospheric emissions continue unabated, the authors warn.聽

鈥�,鈥� Pollard told The New York Times. 鈥淏ut I think we are pointing out that there鈥檚 a danger, and it should receive a lot more attention.鈥澛�

In comparison, the International Panel on Climate Change (IPCC) . 鈥淕lobal sea level is projected to rise during the 21st聽century at a greater rate than during 1961 to 2003,鈥� suggests the IPCC, at a rate of 4 mm per year through the 2090s.聽

And in 2013, the National Oceanic and Atmospheric Administration concluded that there was a 90 percent chance that global mean sea level , 鈥渘o more, no less.鈥� And while NOAA鈥檚 prediction of anywhere between 8 inches and 6.6 feet is a wide rage, they mostly refer to their 鈥溾�� based on projected ocean warming of a 1.6 foot rise. (Which, by the way, is no small obstacle. A recent study published in the journal Nature suggests this estimate alone would displace 13.1 million Americans living in coastal cities.)听

鈥淵ou could think of all sorts of ways that we might duck this one,鈥� Richard Alley, a leading expert on glacial ice at Pennsylvania State University and unaffiliated with the study, told The Times. 鈥淚鈥檓 hopeful that will happen. But given what we know, I don鈥檛 think we can tell people that we鈥檙e confident of that.鈥澛�

But DeConto and Pollard say a rise of five to six feet, the worst-case scenario proposed by NOAA, is a real possibility not to be shrugged off.

鈥淧eople should not look at this as a futuristic scenario of things that may or may not happen,鈥� Eric Rignot, an Earth sciences professor at the University of California, Irvine, who was not involved with the study, told The Chicago Tribune. 鈥淭hey should look at it as the tragic story we are following right now. We are not there yet鈥� [But] with the current rate of emissions, we are heading that way.鈥澛�

DeConto and Pollard鈥檚 study uses new models to account specifically for Antarctic ice sheets, but they are not the first climate scientists to suggest sea level rise predictions by the IPCC and NOAA are underestimates. Just last week, former NASA scientist James Hansen and 18 co-authors published a study suggesting that serious increases in temperature and sea level will likely occur in decades, not centuries. 聽