That becomes clear when you consider what's happening to global sea level. Sea level rises when the oceans get warm because warmer water expands. This accounts for about half of global sea level rise. So with the oceans not warming, you would expect to see less sea level rise. Instead, sea level has risen about half an inch in the past four years. That's a lot.
How do they know if the sea level has risen or if the ground has sunk?