It is no longer news that sea levels are expected to rise over the course of the next century due to climate change driven by human activities. However a new study in Antarctica predicts that things could be worse than we thought.

Two climate scientists claim that previous estimates of sea level rise have been far too low. Robert DeConto at the University of Massachusetts Amherst and David Pollard at Pennsylvania State University say that existing models have “under-appreciated” the extent to which ice in Antarctica is melting.

Antarctica Melt Could See Higher Sea Levels Than Thought

New models predict far higher sea level rises

The paper was published on Wednesday in the journal Nature, and the scientists explain how they looked into the past to better understand the future.

DeConto and Pollar used a 3D ice sheet model to construct an image of how the Earth looked 3 million years ago, in the Pilocene era, and 125,000 years ago, in the Eemian era. During both eras atmospheric carbon dioxide emissions were similar to those found today, but sea levels were 20-30 feet higher.

“So at a time in the past when global average temperatures were only slightly warmer than today, sea levels were much higher,” DeConto says in a press release. “Melting 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.”

“Hydro fracturing” in Antarctica an important factor to consider

The pair claim that existing models underestimate the speed of ice melt in Antarctica, and claim that it will melt as fast as during the Pilocene and Eemian eras. One major point is the fact that existing models do not consider “hydro fracturing,” which sees meltwater cause big chunks of ice to fall from ice shelves.

DeConto and Pollard say that the collapse of these vertical cliffs will be important. “Antarctica has the potential to contribute greater than 1 meter (39 inches) of sea-level rise by the year 2100″ if nothing is done to curb atmospheric emissions..

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

Other bodies predict lower sea levels

By contrast the International Panel on Climate Change (IPCC) predicts a sea level rise of just 0.5 meters over 1990 levels by 2100. “Global sea level is projected to rise during the 21st century at a greater rate than during 1961 to 2003,” suggests the IPCC, claiming the rate will be 4 mm per year through the 2090s.

According to a 2013 announcement the National Oceanic and Atmospheric Administration believes that there is a 90 percent chance that mean sea levels will rise between 0.2 and 2 meters by 2100, “no more, no less.” This prediction ranges between 8 inches and 6.6 feet, the body largely uses its “intermediate-low” scenario which would see a rise of 1.6 feet.

“You could think of all sorts of ways that we might duck this one,” Richard Alley, a leading expert on glacial ice at Pennsylvania State University and unaffiliated with the study. “I’m hopeful that will happen. But given what we know, I don’t think we can tell people that we’re confident of that.”

The NOAA says that a worst case scenario will see a 5-6 feet rise. DeConto and Pollard believe this possibility should not be discounted.

While the new study uses different models, it is not the first piece of research to suggest that predictions from the IPCC and NOAA are low. Last week former NASA scientist James Hansen published a paper suggesting that serious sea level rise will happen within decades rather than centuries.