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Sea Level
Wed Aug 20, 2003
Listen in RealAudio 
Sometimes certain weather terms can be clear as mud. Hi, I'm Bryan Yeaton, and this is the
Weather Notebook. Today's commentator, David Laskin, says one term in particular is hard to
define.
The term "sea level," whether used to calibrate atmospheric pressure or measure mountaintops,
is obvious, right? Maybe not. When you stop to think about it, the concept of sea level
becomes as slippery as, well, water. For starters, because of the tides, sea level changes all
the time, sometimes drastically. In Cook Inlet near Anchorage, for example, the mean tidal
range is 30 feet, and at Canada's Bay of Fundy tides have ranged as much as 53 feet from low
water to high, the world's record.
The deeper you get into it, the more elusive sea level becomes. It turns out that because of
the Gulf Stream, sea level off the coast of Bermuda is nearly 3 and a half feet higher than
off America's East Coast, and that the Pacific side of the Panama Canal is nearly 8 inches
higher than the Atlantic side due to differences in water density and prevailing winds. And of
course, thanks to global warming, there has been a general, though unevenly distributed, rise
in sea levels all around the world - a rise of as much as 8 inches over the past century,
projected to jump another 20 inches in the century to come.
With all this perpetual oceanic sloshing, scientists have to draw the line somewhere. The
National Ocean Service defines sea level as the mean hourly height of the ocean as observed
over a period of 19 years at 175 stations around the country. If you're a sea level purist,
take heart: we're in the midst of a new data-gathering cycle right now.
The Weather Notebook is a production of the Mount Washington Observatory. It is underwritten
by Subaru and the National Science Foundation.
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