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Sea Level Monitoring Maintained by IOC  
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Why measure sea level?
People who live on the coast are familiar with the regular rise and fall of sea level caused by the tides. Many areas also experience rises due to air pressure and winds. As of the last few years, some scientists have been predicting that global warming may also contribute to an overall rise in sea level in the not too distant future. If all these factors converge simultaneously, especially if storm surges combine with high tides, there may be extensive flooding and damage. It is therefore important to continuously monitor sea level. Since ancient times observers of the ocean have attempted the measurement of changes in sea level in order to understand the mechanisms responsible for phenomena such as tides and the catastrophic floods caused by storms and tsunamis. Even prehistoric societies were able to associate regular changes in sea level with movements of the Moon and Sun. In modern times tidal studies have preoccupied some of the world's most outstanding scientists. It is now known that sea level changes occur on all timescales from seconds (due to wind waves) through to millions of years (due to the movement of the continents). In recent decades, the traditional means of sea level monitoring been by using tide gauges that have been installed at various locations along the world's continental coastlines, especially near centres of population. In addition, measurements now can be made in the deep ocean by bottom pressures obtained from seabed devices and by using satellite radar altimetry.
Seasonal and inter-annual changes
The deep ocean changes tell us how the global 'ocean weather' varies from day to day, from season to season as its 'heat content' changes through the year, and from one year to the next. Some of the largest inter- annual changes in sea level occur in the Pacific every 3-4 years as a consequence of El NiƱo events.
Long-term changes in sea level
On longer timescales, the Intergovernmental Panel on Climate Change (IPCC) has concluded, from available evidence, that levels have risen globally by approximately 10-25 cm during the past century, and may increase by 50cm in the next. Such rises could add to problems of protecting against coastal flooding both at continental coastline sites and at ocean islands which are only a few metres above sea level. What action is being taken?'
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What Will Climate Change and Sea Level Rise Mean for Barrier Islands?
by NASA/Goddard Space Flight Center / ScienceDaily
16 June 2011

new survey of barrier islands published earlier this spring offers the most thorough assessment to date of the thousands of small islands that hug the coasts of the world's landmasses.
Read more at http://www.sciencedaily. ... 71412.htm.
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