Rising Sea Level
The level of oceans is rising. Since 1993 the average increase has been approximately 2.6 - 2.9 mm per year. That rate of increase is currently accelerating, likely as a result of global warming, and could cause the oceans to rise by the end of the 21st century, depending on the degree of mitigation implemented to limit release of greenhouse gases, by a conservative estimate of a total rise of at least 52 - 98 centimeters. Other estimates place the total rise at 0.3 - 2.5 meters.
The two main causes of increasing sea levels are (1) expansion due to increasing heat content of the oceans and (2) melting of glaciers and polar ice caps.