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Index of Subjects For detailed discussion of land sinking/rising, and of determining actual mean sea level (MSL) changes over time as a result of measurements that largely originate from multiple tide gauges, try this (1995) review: http://www.agu.org/revgeophys/dougla01/node3.html According to this site, local sea level is rising rapidly by 3.5 mm per year near Baltimore because the local land is sinking. Because of a sort of amplification effect explained in the article, a change of 1 mm can result in devastating effects 50-200 times larger, as has happened in nearby Chesapeake Bay. Oppositely, local sea level is falling rapidly by 4 mm per year at Stockholm because of continuing post-glacial rebound (the land is rising after a heavy ice-age load). Nothing is mentioned in the article on the situation further north from Baltimore in NS, but presumably NS is more like Sweden. The more reliable tide gauge data are said to indicate a rise of 1.8 mm per year in MSL, averaged worldwide. At least in 1995, this guy seemed to think this rate of rise was not obviously accelerating, but I suspect that this conclusion may be out of date. On 7-Mar-07, at 3:52 PM, Gerald Ruderman wrote: > Paul, > I am curious where you learned that GPS uses atmospheric pressure for > altitude. > > My GPS gives me altitude when it has good signals from 4 satellites. > When it only has 3 it only give me position on the geoid. GPS receivers > have no way to send anything to the satellites. > > Atmospheric pressure is important at airports because planes most basic > altitude measurement is by pressure. > Gerald
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