World oceans rising dangerously, says NASA

Oceans around the world are rising dangerously, warns NASA, adding that the ramifications of sea level rise can be even scarier than the worst-case scenarios predicted by climate models.

Seas around the world have risen an average of nearly three inches since 1992, with some locations rising more than nine inches due to natural variation, according to the latest satellite measurements from NASA and its partners.

"Given what we know now about how the ocean expands as it warms and how ice sheets and glaciers are adding water to the seas, it's pretty certain we are locked into at least three feet of sea level rise, and probably more," explained Steve Nerem from the University of Colorado, Boulder, and leader of the "Sea Level Change" team.

"But we don't know whether it will happen within a century or somewhat longer," he added.

In 2013, the United Nations Intergovernmental Panel on Climate Change (IPCC) issued an assessment based on a consensus of international researchers that stated global sea levels would likely rise from 1 to 3 feet by the end of the century, a NASA statement read.

According to Nerem, new research suggests the higher end of that range is more likely and the question remains how that range might shift upward.

The data, however, reveals the height of the sea surface is not rising uniformly everywhere as of now.

"Sea level along the west coast of the United States has actually fallen over the past 20 years because long term natural cycles there are hiding the impact of global warming," added Josh Willis, oceanographer at NASA's Jet Propulsion Laboratory (JPL) in Pasadena, California.

However, there are signs this pattern is changing.

"We can expect accelerated rates of sea level rise along this coast over the next decade as the region recovers from its temporary sea level 'deficit,'" Willis added.

Scientists estimate that about one-third of sea level rise is caused by expansion of warmer ocean water, one-third is due to ice loss from the massive Greenland and Antarctic ice sheets, and the remaining third results from melting mountain glaciers.

But the fate of the polar ice sheets could change that ratio and produce more rapid increases in the coming decades.

The Greenland ice sheet, covering 660,000 square miles -- nearly the area of Alaska -- shed an average of 303 gigatons of ice a year over the past decade, according to satellite measurements.

The Antarctic ice sheet, covering 5.4 million square miles - larger than the US and India combined -- has lost an average of 118 gigatons a year.

Although Antarctica's contribution to sea level rise is currently much smaller than that of Greenland, recent research indicates this could change in the upcoming century.