According to National Geographic, the annual rate of sea level rise over the past 20 years has been 0.13 inches a year, roughly twice the average speed of the preceding 80 years. This is due to human activity that results in the thermal expansion of sea water, the melting of glaciers and polar icecaps, and the melting of the Greenland ice sheet.
The result is the flooding of wetlands, contamination of aquifers and agricultural soils, and lost of habitat for fish, birds, and plants. Higher sea level, combined with more intense storms (e.g., super storm Sandy) create much greater storm surges.
The result will be far more than property losses. As more of the coast is gradually lost to the sea, there will be a great migration inland, putting evermore demands on limited resources.
How bad could it be? A recent study says we can expect the oceans to rise between 2.5 and 6.5 feet by 2100, enough to swamp many of the cities along the U.S. East Coast. Should a complete meltdown of the Greenland ice sheet occur, sea level could rise to 23 feet, submerging London.