It seems like every few months there is another announcement that this or that glacier in Greenland or Antarctic is melting because of global warming and sea level is going to go up an additional 0.3 m (1 foot) or 3 m (10 feet) or 30 m (100 feet) by the time its all over. But there is another curious factor involved in determining just how high sea level will rise, and thats gravity.
Most people accept that gravity is pulling objects toward the center of earth---even climate change skeptics are familiar with that much science. But not as well known is the fact that mountains and even continents exert a gravitational force on every thing around them so that things are pulled ever-so-slightly sideways by gravity towards the nearest mountain range, or if you're on a boat there is a tiny gravitational attraction being exerted by the nearest land standing above the ocean.
For the most part these lateral gravitational forces are small and are safely ignored, but if something really large like part of a continent could rapidly appear or disappear on the surface of the earth, then this would abruptly change the lateral effects of gravity in significant ways.
Huge amounts of glacier ice are projected to melt and disappear from Antartica and Greenland over the next few hundred years, and this will reduce their gravitational attraction on nearby parts of the ocean. By far the largest effect will be felt around Antartica, where so much ice will melt over the next several centuries that it is estimated that local sea level in the surrounding Southern Ocean will fall by about 3 m. And where will all that extra ocean water go after the ice melt? Geophysical models suggest it will be distributed mostly to the northern hemisphere, where it will cause sea level around the shoreline of North America to rise about 3 m (10 feet) higher then the ocean would reach just due to ice melt alone.
Of course it will take several hundred years for global warming to melt enough ice from the ice sheets in Greenland and Antarctica to cause sea level to rise by 25-30 m (75-100 feet). By that time sea level rise will have destroyed so many coastal cities in the U.S. and around the world that having the ocean go another 3 m (10 feet) higher in the northern hemisphere due to the reduced gravitational attraction on seawater around Antarctica will probably be seen as no big deal.
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