NASA teleconference on sea level change warns of rising oceans
On Aug. 26, NASA held a media teleconference regarding current predictions on sea level rise, highlighting the risks to coastal populations in low-lying areas, and the inherent problems in creating reliable global models. A panel of experts from NASA's recently-founded Sea Level Change Team tells us that ocean levels are inexorably on the rise, but gaps in our understanding and ability to survey risk regions mean we don't know just how fast the change will take place.
"People need to beprepared for sea level rise, we're going to continue to have sealevel rise for decades and probably centuries, it's not going tostop, the question is how fast is it going to be?" states JoshWillis, climate scientist at NASA’s Jet Propulsion Laboratory (JPL)in Pasadena, California. "If you live on a coastline, or youhave some economic dependence on a coastline, we have to be preparedfor rising seas, it's not a question of how much, but rather when."
The board stated thatthe rise in ocean levels is coming from three distinct sources. Thefirst is thermal expansion, in which ocean water expands as itis heated, taking up more volume and causing sea levels to rise. Thiseffect has been exacerbated by greenhouse gas emissions, of which theocean absorbs over 90 percent of the resultant heat.
The second source isice loss from the Greenland and Antarctic ice sheets, while the finalthird is from melting mountain glaciers. Ice sheets and glaciers canbe lost from contact with warmer air, the creation of icebergs, orfrom interaction with warm sea water. It is estimated that theGreenland ice sheet alone has lost around 303 gigatons of mass peryear for the last decade.
We are aware of thisthanks to a number of scientific instruments wielded by NASA and itspartners. A notable contributor to our knowledge has been the Jason 1& 2 and TOPEX/Poseiden satellites, whose altimeters have allowedfor incredibly precise measurements. Simultaneously NASA's GRACEsatellite has been observing Earth's gravitational field, takingaccurate measurements in order to determine by how much ice sheetsand glaciers are shrinking.
Data from thesesatellite missions and other resources tell us that our oceans haverisen by about 8 inches (203 mm) since the onset of the 20thcentury, and that we may be facing a rise in excess of 3 ft (0.9m) before the centuryis out. A visual representation of the phenomenon is presentedin the video below (starting at the 40-second mark), which draws on data from 23 years of satelliteobservations, the result of a collaboration between NASA and theFrench space agency Centre National d'Études Spatiales.
The visualrepresentation shows us that water is not rising at a global standardrate. Instead there are significant levels of variation and in someisolated pockets, the water level is actually subsiding, as evidencedby the rare blue patches. It is however worth noting that thesediscrepancies are due to identifiable ocean mechanics.
"Sea level along thewest coast of the United States has actually fallen over the past 20years because long-term natural cycles there are hiding the impact ofglobal warming," explains Willis. "However, there are signs thispattern is changing. We can expect accelerated rates of sea levelrise along this coast over the next decade as the region recoversfrom its temporary sea level 'deficit.'"
During theteleconference, the panel of experts was keen to point out a majorflaw in our ability to create accurate models of sea level rise –our lack of understanding regarding the role that the degradation ofEast Antarctica's leviathan ice sheet has on rising sea levels. Thisis due to the fact that many of the changes taking place with the icesheets occur under the water line, making it very difficult toobserve them from space.
"The prevailing viewamong specialists has been that East Antarctica is stable, but wedon’t really know," states Eric Rignot, a glaciologist at theUniversity of California Irvine and JPL. "Some of the signs we seein the satellite data right now are red flags that these glaciersmight not be as stable as we once thought. There’s always a lot ofattention on the changes we see now, but as scientists our priorityneeds to be on what the changes could be tomorrow."
Simply put, currentequipment must reach a greater level of sophistication, with computermodels needing to be run at a higher resolution than the currentgeneration of computers can handle. This summer, in an attempt toincrease our understanding of the impact that ice sheets are having,NASA initiated a six-year field campaign, Oceans Melting Greenland(OMG), to study how warmer ocean waters are affecting the Greenlandice sheet. By combining satellite imaging with terrestrial basedcampaigns like OMG, NASA hopes to generate more accurateforecasts.
The teleconferencepaints a grim picture of what can be expected in the decades andcenturies to come, and the question was raised as to how theinformation can be acted upon now. Eleven of the world's largestcities are situated on coastal regions, and in America alone, around160 million people live on the country's shores. The danger is notconfined to seawater flooding low-lying coastal areas – rising seas could have an affect on extreme weather systemssuch as hurricanes, which will be able to project their influenceever farther inland.