NASA Satellites Detect Pothole on Road to Higher Seas

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Alan Buis 818-354-0474
Jet Propulsion Laboratory, Pasadena, Calif.
Alan.buis@jpl.nasa.gov

Feature: 2011-262 Aug. 23, 2011

An Update from NASA's Sea Level Sentinels:
NASA Satellites Detect Pothole on Road to Higher Seas

The full version of this story with accompanying images is at:
http://www.jpl.nasa.gov/news/news.cfm?release=2011-262&cid=release_2011-262

Like mercury in a thermometer, ocean waters expand as they warm. This, along with melting
glaciers and ice sheets in Greenland and Antarctica, drives sea levels higher over the long term.
For the past 18 years, the U.S./French Jason-1, Jason-2 and Topex/Poseidon spacecraft have
been monitoring the gradual rise of the world's ocean in response to global warming.

While the rise of the global ocean has been remarkably steady for most of this time, every once
in a while, sea level rise hits a speed bump. This past year, it's been more like a pothole: between
last summer and this one, global sea level actually fell by about a quarter of an inch, or half a
centimeter.

So what's up with the down seas, and what does it mean? Climate scientist Josh Willis of
NASA's Jet Propulsion Laboratory, Pasadena, Calif., says you can blame it on the cycle of El
Niño and La Niña in the Pacific.

Willis said that while 2010 began with a sizable El Niño, by year's end, it was replaced by one of
the strongest La Niñas in recent memory. This sudden shift in the Pacific changed rainfall
patterns all across the globe, bringing massive floods to places like Australia and the Amazon
basin, and drought to the southern United States.

Data from the NASA/German Aerospace Center's twin Gravity Recovery and Climate
Experiment (Grace) spacecraft provide a clear picture of how this extra rain piled onto the
continents in the early parts of 2011. "By detecting where water is on the continents, Grace
shows us how water moves around the planet," says Steve Nerem, a sea level scientist at the
University of Colorado in Boulder.

So where does all that extra water in Brazil and Australia come from? You guessed it--the
ocean. Each year, huge amounts of water are evaporated from the ocean. While most of it falls
right back into the ocean as rain, some of it falls over land. "This year, the continents got an extra
dose of rain, so much so that global sea levels actually fell over most of the last year," says
Carmen Boening, a JPL oceanographer and climate scientist. Boening and colleagues presented
these results recently at the annual Grace Science Team Meeting in Austin, Texas.

But for those who might argue that these data show us entering a long-term period of decline in
global sea level, Willis cautions that sea level drops such as this one cannot last, and over the
long-run, the trend remains solidly up. Water flows downhill, and the extra rain will eventually
find its way back to the sea. When it does, global sea level will rise again.

"We're heating up the planet, and in the end that means more sea level rise," says Willis. "But El
Niño and La Niña always take us on a rainfall rollercoaster, and in years like this they give us
sea-level whiplash."

For more information on NASA's sea level monitoring satellites, visit:
http://sealevel.jpl.nasa.gov/ , http://sealevel.colorado.edu , http://www.csr.utexas.edu/grace/ and
http://grace.jpl.nasa.gov/ .

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