WASHINGTON: Oceans around the world have risen an average of nearly eight centimetres since 1992, with some locations rising more than 25 centimetres due to natural variation, according to the latest satellite measurements by NASA.
An intensive research effort now underway, aided by NASA observations and analysis, points to an unavoidable rise of several feet in the future.
“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 3 feet (0.9 meter) of sea level rise, and probably more,” said Steve Nerem of the University of Colorado, Boulder, and lead of the Sea Level Change Team.
“But we don’t know whether it will happen within a century or somewhat longer,” said Nerem.
The record is based on data from three consecutive satellite missions; the first a collaboration between NASA and the French space agency, Centre National d’Etudes Spatiales (CNES), launched in 1992.
In 2013, the United Nations Intergovernmental Panel on Climate Change issued an assessment based on a consensus of international researchers that stated global sea levels would likely rise from 0.3 to 0.9 meter by the end of the century.
According to Nerem, new research available since this report suggests the higher end of that range is more likely, and the question remains how that range might shift upward.
The data reveal the height of the sea surface is not rising uniformly everywhere. Regional differences in sea level rise are dominated by the effects of ocean currents and natural cycles such as the Pacific Decadal Oscillation.
But, as these natural cycles wax and wane, they can have major impacts on local coastlines.
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 1.7 million square kilometres shed an average of 303 gigatons of ice a year over the past decade, according to satellite measurements.
The Antarctic ice sheet, covering 14 million square kilometres has lost an average of 118 gigatons a year.
“We’ve seen from the paleoclimate record that sea level rise of as much as 10 feet [3 meters] in a century or two is possible, if the ice sheets fall apart rapidly,” said Tom Wagner, the cryosphere programme scientist at NASA Headquarters in Washington.
“We’re seeing evidence that the ice sheets are waking up, but we need to understand them better before we can say we’re in a new era of rapid ice loss,” said Wagner.
Although Antarctica’s contribution to sea level rise currently is much smaller than that of Greenland, recent research indicates this could change in the upcoming century.
Sent from my Tricorder