The two major causes of global sea level rise are thermal expansion of the oceans (water expands as it warms) and the loss of land - based ice due to increased melting. (ipcc.ch)
The average annual rate of global sea level rise accelerated from 1993 - 2008, increasing 65 - 90 percent above the twentieth century average. (ucsusa.org)
Not subject to urban heat island effects, the trend in global sea ice extent is a primary indicator of climate change, or the lack thereof. (climatechangefacts.info)