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article imageRising global sea levels – upward trend resumes, reports NASA

By Robert Myles     Nov 19, 2012 in Environment
In a study issued today, NASA has reported that global sea levels have resumed their long term upward trend after a blip in 2010/11. The study was based on multi-sourced data from NASA and European Topex/Poseidon, Jason-1 and Jason-2 satellites.
Towards the end of summer 2011, in a report entitled NASA Satellites Detect Pothole on Road to Higher Seas, NASA's Jet Propulsion Laboratory and the University of Colorado in Boulder reported that the almost continuous rise in global sea levels observed since 1992 appeared to have gone into decline. In 2010, global sea levels dropped by 5 millimetres. It transpires that the decline may have been transient in nature, the result of a strong La Niña event caused by the Pacific La Niña ocean/atmospheric climatic system. In their latest report What Goes Down Must Come Back Up, NASA says the long term upward trend, averaging a rise of 3.2 millimetres per annum over the last 20 years has now resumed.
The sharp fall in global sea levels recorded between early 2010 and summer 2011 was due to a very strong La Niña. This periodic, but irregular, Pacific Ocean climatic system altered rainfall patterns worldwide. As a consequence, vast amounts of water were moved from the ocean to the continents primarily affecting Australia, northern South America and Southeast Asia.
A paper recently published in the journal Geophysical Research Letters traces the effects of the 2010-11 La Niña on global sea levels. The data show that not only has the global average sea level recovered from the more than 0.2 inches (5 millimetres) drop in 2010/11, but also that the long term average annual rise in global sea levels has been resumed.
NASA has prepared a graphical illustration of the new study, reproduced below.
This graphic shows changes in global mean sea level as measured by satellite altimetry (NASA/CNES Topex/Poseidon and Jason-1; and NASA/CNES/NOAA/EUMETSAT Jason-2) between 1992 and 2012. The data have been averaged to account for long time scale variations in sea level. The average annual increase in sea level over this timeframe, depicted by the blue line, is 3.2 millimetres per year. The inset shows changes in Earth's water mass from the beginning of 2010 to mid 2011. Blue colours indicate an increase in water mass over the continents. The new NASA study shows that most of the sea level drop in 2010-11 (circle in red) was related to the mass transport of water from the ocean to the continents (primarily Australia, northern South America and Southeast Asia as indicated by blue arrows). While the ocean "lost" water, the continents experienced a gain because of increased rainfalls brought on by the 2010/11 La Niña.
Said lead study author, Carmen Boening of JPL. "The water the ocean 'lost' was compensated for rather quickly. The newest data clearly indicate that the drop in 2010-11 was only temporary."
Co-author of the report, Josh Willis of JPL added, “Like clockwork, the long-term rise of the ocean marches on. The dip in global sea levels, brought to us courtesy of a major La Niña event, was little more than a pothole in the long road toward a rising ocean and shrinking coastlines,"
The resumption of the upward trend in global sea levels will have repercussions for disaster planning worldwide. With each passing year, tropical storms and hurricanes are starting, on average, with a higher baseline when it comes to sea levels. As higher sea levels have a knock-on effect causing a greater volume of water in storm surges, this will increase the frequency of coastal flooding and the likelihood of coastal defences being inundated in the future.
This year’s ‘Frankenstorm,’ Hurricane Sandy, may turn out to be the harbinger of greater problems ahead.
More about Global warming, Rising sea levels, Rising sealevels, Climate change, NASA
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