NASA researchers measure sea levels, predict faster rise

A new worldwide map of sea level rise, plotted with precision satellite instruments, shows that the Earth’s oceans are rising faster with no end in sight.

Sea levels have gone up an average of 3 inches since 1992, with some locations rising as much as 9 inches. Meanwhile, some limited areas — including the West Coast — have experienced declining sea levels for various reasons.

Sea level change over 22 years. Map: NASA
Sea level change over 22 years. (Click to enlarge) // Map: NASA

Two years ago, climatologists released an international consensus, which predicted a sea-level rise of between 1 and 3 feet by the end of this century. It was a conservative estimate, and new evidence suggests that ocean waters are likely to meet or exceed the top of that range, possibly going much higher, according to four leading researchers speaking at a news conference yesterday.

The implications are huge and growing more important all the time. At a minimum, waterfront property owners and shoreline planners need to begin taking this into consideration. It doesn’t make sense to build close to the shoreline if extreme high tides will bring seawater to one’s doorstep.

If we hope to avoid local extinctions of key intertidal species, we must start thinking about how high the waters will be in 50 to 100 years.

For clues to the future, we can watch Florida, where vast areas stand at low elevations. Even now, during high tides, Miami is beginning to see regular flooding in areas that never got wet before. This is the future of low-lying areas in Puget Sound, such as estuaries. In the Pacific ocean, the threat of inundating complete islands is becoming very real.

Along the West Coast, sea levels have actually declined over the past 20 years, largely because of the cooling effect of the Pacific Decadal Oscillation, a warming/cooling cycle that can remain in one phase for decades. The cycle appears to be shifting, with the likely effect that sea levels on the West Coast will soon rise as fast or faster than the worldwide average, according to Josh Willis, an oceanographer at NASA’s Jet Propulsion Laboratory in Pasadena, Calif.

Global sea level has been measured accurately and continuously by satellites since 1993. Graphic: Steve Nerem, University of Colorado
Global sea level has been measured accurately and continuously by satellites since 1993.
Graphic: Steve Nerem, University of Colorado

The cause of sea level rise is attributed to three factors. Scientists estimate that roughly one-third of the rise is caused by thermal expansion of ocean waters, which absorb much of the energy from global warming. Another third comes from the melting of the massive Greenland and Antarctic ice sheets. The remaining third comes from the melting of mountain glaciers throughout the world. Researchers at yesterday’s news conference said they expect the melting to accelerate.

Measuring the change in sea-level rise has become possible thanks to advanced technology built into altimeters carried aboard satellites. The instruments can distinguish changes in elevation as small as one part in 100 million.

“The instruments are so sensitive that if they were mounted on a commercial jetliner flying at 40,000 feet, they could detect the bump caused by a dime lying flat on the ground,” said Michael Freilich, director of NASA’s Earth Science Division.

While sea level rise can now be measured, predicting the rate of future rise is difficult, because much of the melting by ice sheets occurs out of sight under the water.

The Greenland ice sheet covers 660,000 miles — nearly the size of Alaska. Satellite measurements have shown that an average of 303 gigatons of ice have melted each year over the past decade. The Antarctic ice sheet has lost an average of 118 gigatons per year, but some new studies suggest it could begin to melt much faster.

In Greenland, researchers are reporting that one of the largest chunks of ice ever to break away from land cleaved from the Jakobshavn glacier in a “calving” event that left researchers awestruck. More than 4 cubic miles of ice was loosed quickly into the sea. Check out the news release by the European Space Agency.

“This is a continuing and evolving story,” glaciologist Eric Rignot said during yesterday’s news conference. “We are moving into a set of processes where we have very tall calving cliffs that are unstable and start fracturing and break up into icebergs …

“We have never seen something like this on that scale before,” said Rignot, associated with JPL and the University of California at Irvine. “Personally, I am in awe at seeing how fast the icefall, the calving part of the glacier, is retreating inland year by year.”

Other new information from NASA, including lots of graphics:

The following video tells the basic story about sea level rise.

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