It's all so confusing: CSM says global sea levels rose about 1/2 inch PER 25 YEARS from 1950 to 2009; now The Economist suggests global sea levels will rise almost 1/2 inch EVERY YEAR between now and 2100

Rising sea levels: Difference Engine: Canute's courtiers | The Economist

Whether North Carolina’s officials approve or not, though, there can be no denying that sea levels around the world are rising rapidly, especially along the Atlantic coast of America. In the past century, the global climate has warmed by about 1ºC. And as the Earth has become warmer, the sea level has risen by one or two millimetres a year.

Lately, however, this rise has put on a spurt. Satellite observations over the past two decades record an increase of three to four millimetres a year. Like it or not, the only explanation for this acceleration is the amount of greenhouse gases being emitted by human activity.
In a report published on June 22nd 2012, the National Research Council of Washington, DC, said it expects the sea level along the Californian coast to rise by about 40 inches over the rest of the century—broadly in line with the global average.

Christian Science Monitor says global sea levels rose at a rate of 2 inches PER CENTURY from 1950 to 2009