NASA: Rising Sea Levels More Dangerous Than Thought

Tia Ghose LiveScience.com Yahoo News 27 Aug 15;

Scientists are concerned about sea level rise from ice melt in southern Greenland (shown here) and the Antarctic.

The consequences of global sea level rise could be even scarier than the worst-case scenarios predicted by the dominant climate models, which don't fully account for the fast breakup of ice sheets and glaciers, NASA scientists said today (Aug. 26) at a press briefing.

What's more, sea level rise is already occurring. The open question, NASA scientists say, is just how quickly the seas will rise in the future.

Rising seas

The current warming of the seas and the associated expansion of their waters account for about one-third of sea level rise around the world.

"When heat goes under the ocean, it expands just like mercury in a thermometer," Steve Nerem, lead scientist for NASA's Sea Level Change Team at the University of Colorado in Boulder, said in the press briefing.

The remaining two-thirds of sea level rise is occurring as a result of melting from ice sheets in Greenland and Antarctica and mountain glaciers, Nerem said.

Data collected by a cadre of NASA satellites — which change position in relation to one other as water and ice on the planet realign and affect gravity's tug — reveal that the ocean's mass is increasing. This increase translates to a global sea level rise of about 1.9 millimeters (0.07 inches) per year, Nerem said.

Unpredictable pace

But the speed of sea level rise is an open question.

"Ice sheets are contributing to sea level rise sooner, and more than anticipated," said Eric Rignot, a glaciologist at the University of California, Irvine, and NASA's Jet Propulsion Laboratory in Pasadena, California.

That's because people have never seen the collapse of a huge ice sheet and therefore don't have good models of the effects, Rignot said.

The Intergovernmental Panel on Climate Change, an international organization created by the United Nations that produces climate change models, has predicted that sea levels could rise as much as 21 feet (6.4 meters) in the next century if global warming continues unabated.

But even that worst-case scenario may not capture the risk, Rignot said. That's because the IPCC models only take into account temperature changes at the surface of glaciers, but not the rapid melting that occurs when glaciers calve and break up into the ocean, Rignot said.

In addition, much of glaciers' melting occurs at deep, undersea ice canyons. Warmer water is salter 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, said Josh Willis, an oceanographer at JPL in Pasadena, California.

When the massive Jakobshavn glacier in Greenland calved earlier this summer, it moved 4.6 square miles (12 square kilometers) of ice in one day, Rignot said.

If the Jakobshavn glacier had melted completely, "it contains enough ice to raise global sea level by half a meter — just this one glacier in Greenland," Rignot said. If all the land ice on the planet were to melt, it would raise sea levels about 197 feet (60 m), he added.

Some of the melting that has already occurred is likely irreversible, and could take hundreds of years to reverse, Rignot said.

American impact

While global sea levels have risen about 2.75 inches (7 centimeters) over the past 22 years, the west coast of the United States has not seen much of a rise in ocean levels. That's largely because of a long-time-scale weather pattern called the Pacific Decadal Oscillation, which is masking the global effect. That, however, could reverse in the coming years, Willis said.

"In the long run, we expect the sea levels on the west coast to catch up to global mean and even exceed the global mean," Willis said.

Florida is also particularly vulnerable to sea level rise because its porous soil allows more seawater intrusion than does the soil in other coastal areas, Willis said.

Global sea levels climbed 3 inches since 1992, NASA research shows
Irene Klotz PlanetArk 27 Aug 15;

Sea levels worldwide rose an average of nearly 3 inches (8 cm) since 1992, the result of warming waters and melting ice, a panel of NASA scientists said on Wednesday.

In 2013, a United Nations panel predicted sea levels would rise from 1 to 3 feet (0.3 to 0.9 meters) by the end of the century. The new research shows that sea level rise most likely will be at the high end of that range, said University of Colorado geophysicist Steve Nerem.

Sea levels are rising faster than they did 50 years ago and "it's very likely to get worse in the future," Nerem said.

The changes are not uniform. Some areas showed sea levels rising more than 9 inches (25 cm) and other regions, such as along the U.S. West Coast, actually falling, according to an analysis of 23 years of satellite data.

Scientists believe ocean currents and natural cycles are temporarily offsetting a sea level rise in the Pacific and the U.S. West Coast could see a significant hike in sea levels in the next 20 years.

"People need to understand that the planet is not only changing, it's changed," NASA scientist Tom Wagner told reporters on a conference call.

"If you're going to put in major infrastructure like a water treatment plant or a power plant in a coastal zone ... we have data you can now use to estimate what the impacts are going to be in the next 100 years," Wagner said.

Low-lying regions, such as Florida, are especially vulnerable, added Michael Freilich, director of NASA's Earth Science Division.

"Even today, normal spring high tides cause street flooding in sections of Miami, something that didn't happen regularly just a few decades ago," Feilich said.

More than 150 million people, mostly in Asia, live within 3 feet (1 meter) of the sea, he added.

The biggest uncertainty in forecasting sea level rise is determining how quickly the polar ice sheets will melt in response to warming temperatures.

"Significant changes are taking place today on ice sheets," said Eric Rignot, a glaciologist at the University of California in Irvine. "It would take centuries to reverse the trend of ice retreat."

Scientists said about one-third of the rise in sea levels is due to the expansion of warmer ocean water, one-third to ice loss from the polar ice sheets and the remaining third to melting mountain glaciers.

(Editing by David Adams and Cynthia Osterman)