Even 40 years ago when scientists starting researching the harsh glacial environment in Antarctica, they identified the melting of the continent’s ice sheets as the single largest threat of rapid sea level rise.

Two groups of US-based scientists now report findings that reaffirm those early concerns.

One of the studies, funded by NASA and the University of California, says the West Antarctic ice sheet is melting faster than most scientists had expected. Glaciologist Eric Rignot, lead author of the NASA study, said the findings will require an upward revision to current predictions of sea level rise.

“This sector will be a major contributor to sea level rise in the decades and centuries to come,” Rignot said in a statement issued by NASA Monday. “A conservative estimate is it could take several centuries for all of the ice to flow into the sea.” The research looked at a rapidly melting section of the giant West Antarctica ice sheet and it “appears to be in an irreversible state of decline.” The melting occurs as warm ocean water flows under the part of the glacier that extends over the water from the land.

The study, which has been accepted for publication this week in the journal Geophysical Research Letters, looked at multiple lines of evidence regarding the Amundsen Sea sector of West Antarctica ice sheet.

The findings of the study require current predictions of sea level rise to be revised upward, Rignot said.

The most recent UN Intergovernmental Panel on Climate Change (IPCC) report estimates that by 2100, sea level will rise somewhere from just less than 26 centimetres to about 98 centimetres. This is more than enough to cause underground systems in coastal cities such as New York City to flood, according to researchers. But the IPCC and other projections do not take into account the possibility of major ice loss in Antarctica.

Rignot said the new study suggests sea level rise projections for this century should lean toward the high-end of the IPCC range.

The other new study comes from the University of Washington whose researchers used detailed topography maps and computer modelling to look at Antarctica’s Thwaites glacier.

It is likely to disappear in the next several hundred years, raising sea level by about 60 centimetres, the researchers said. That glacier acts as a linchpin on the rest of the ice sheet, which contains enough ice to cause another 3 to 4 metres of global sea level rise.

The study will be published Friday in Science.

There’s been a lot of speculation about the stability of the ice sheets, with many scientists suspecting that the melting is well under way, said lead author Ian Joughin, a glaciologist at the University of Washington.

“This study provides a more quantitative idea of the rates at which the collapse could take place,” Joughin said.

The fastest the “collapse” would occur is 200 years, but it could take more than 1,000 years, the research concluded. The University of Washington also suggested that the collapse may be inevitable.

“Previously, when we saw thinning we didn’t necessarily know whether the glacier could slow down later, spontaneously or through some feedback,” Joughin said.

“In our model simulations it looks like all the feedbacks tend to point toward it actually accelerating over time; there’s no real stabilizing mechanism we can see.” The ice sheet has been studied over more than 40 years by many US researchers, all of whom asked the same question: Is the West Antarctic ice sheet disintegrating? Research published in 1981 by Terry Hughes of the University of Maine called the Amundsen Sea region “the weak underbelly of the West Antarctic ice sheet.” The underbelly is a reference to the fact that nearly all glacier melt occurs on the underside of the glacier beyond the grounding line, or the point on a glacier where it loses contact with land.

The defining characteristic of West Antarctica is that the majority of the ice sheet is “grounded” on a bed that lies below sea level.

When the ice sheet is attached to a bed below sea level, ocean currents can deliver warm water to the grounding lines.

In the potential chain reaction that can result, NASA said, is the ocean heat eats away at the ice and the sheet loses mass. When that occurs it loses the ability to hold back inland glaciers from sliding into the sea, meaning those glaciers can accelerate and thin.

This thinning, NASA explained, is conducive to the grounding line retreating even farther inland, bringing more acceleration and more thinning. In this equation, more ice flows to sea every year and sea level rises.