Sea level is bumpy, but it rising overall as polar and glacial ice melts. This image shows TOPEX sea level data in Eastern Equatorial Pacific from Dec. 4, 1997, during an El Nino event (visible as high red surface). Image courtesy of NASA/Goddard Space Flight Center Scientific Visualization Studio

Satellite tracking of the oceans and the melting of ice sheets and glaciers from 2005 to 2011 now confirms that the seas worldwide have risen 2.39 millimeters per year over that seven-year period, and hasn’t stopped. That’s almost 17 millimeters over those seven years, or more than 5/8ths of an inch, about the width of a typical adult index finger at the first knuckle.

It seems small until you add it up over decades past and those to come. It’s especially no small matter to those people living near sea level, on an atoll or along a coast, where every inch is of concern. All one needs is a storm surge — as that seen during Superstorm Sandy — and the steady rise of sea level becomes painfully clear.

There is also the matter of those places where the land is also sinking, which is common along the Gulf Coast, for instance. Sinking land increases the effective sea level rise in those places. In New Orleans, for instance, satellite data has shown that different parts of the city are sinking at rates ranging from 1.79 to more than 15 millimeters per year. Tack on another 2.39 millimeters to those numbers to get a general idea of how much sea level is rising relative to the ground under the Big Easy.

To confirm the global sea level rise number, a team of researchers led by the University of Texas’ Jianli Chen used gravity data from the GRACE satellites to estimate changes in ocean mass between 2005 and 2011 — since all mass also has gravity, any changes in gravity over oceans is basically a change in the water mass. They showed that the ocean mass increased enough for a 1.8 mm rise in sea level per year, due mostly to the melting of ice in Greenland and Antarctica as well as mountain glaciers.

Then they factored in changes in the density of the oceans using data from a network of oceans floats. They found that a drop in water density — usually that means warming water — over the same period led to a sea-level rise of about 0.6 millimeters per year. Add that to the the 1.8 mm per year and you have a number that matches a figure calculated by other researchers using totally different data from different satellite sensors.

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