NASA scientists believe the worst case scenario predictions of sea level rises given to date have been vastly understated as a result of not taking into consideration the fast breakdown of glaciers and ice sheets.
They also say sea level rise is already happening but one question they have not yet been able to answer is how quickly will seas rise going forward.
The lead scientist for NASA's Sea Level Change Team at the University of Colorado in Boulder, Steve Nerem, said the current sea warming and the associated water expansion accounts for one-third of global sea level increases, with the other two thirds happening as a result of melting Greenland ice sheets, mountain glaciers and Antarctica.
"When heat goes under the ocean, it expands just like mercury in a thermometer," he said.
Nerem said NASA satellite data shows ocean mass is increasing with worldwide sea levels rising 0.07 inches per year.
Eric Rignot, a glaciologist at NASA's Jet Propulsion Laboratory said "Ice sheets are contributing to sea level rise sooner, and more than anticipated" because as the collapse of huge ice sheets have never been observed before there are no models of its effect.
A recent United Nation's (UN) report predicted a sea level rise of 21 feet within the next 100 years if the rate of global warming did not abate.
But according to Rignot even that worst-case scenario may not capture the real risk as all predictions to date have only considered temperature changes at glacier surfaces and not the "rapid melting" that happens when glaciers calve, breaking up into the ocean.
Jet Propulsion Lab oceanographer Josh Willis added most glacier melting happens in deep, underwater ice canyons where sea level activity can not be observed or measured.
"Warmer water is saltier and therefore heavier. That means it sinks into the deeper layers of the ocean, and the contrast between this warm water and the undersea ice canyons contributes an unknown but substantial amount of sea level rise." he said.