If Sea Levels had risen 7" over the past century, then the 3' rise over the next century would not be implausible. However, it is highly questionable whether sea levels have done so. Local measurements vary all over the world, as crust plates rise and fall. The earth is still stretching back from the deformation due to the weight of the last ice age's ice sheets (springing up where the ice existed, and subsiding in neighboring areas where the ice did not exist), populated lands are falling due to local use of ground water, and California is of course geologically active. Also, continental coasts see varying sea levels due to winds and currents, notably El Nino in the Pacific. Most mid-ocean islands have not seen sea level rises, and there has been considerable sea level fall in much of the Indian Ocean over the past 2 or 3 decades.
Nice analysis in post 70.
However, you still bent to the will of the parrot flock a little.
You make a good case for the sea levels not rising at all, but what you do not say is that your case also allows for a rise of even bigger than 7 inches over the last century.