Basically, that the use of waterlines from the Pliocene era to estimate CAGW induced sea level rise are inaccurate due to their failure to account for plate tectonics causing land levels to rise.

http://www.sciencemag.org/content/ea...cience.1229180

Sedimentary rocks from Virginia through Florida record marine flooding during the mid-Pliocene. Several wave-cut scarps that at the time of deposition would have been horizontal are now draped over a warped surface with a maximum amplitude of 60 m. We modeled dynamic topography using mantle convection simulations that predict the amplitude and broad spatial distribution of this distortion. The results imply that dynamic topography and, to a lesser extent, glacial isostatic adjustment, account for the current architecture of the coastal plain and proximal shelf. This confounds attempts to use regional stratigraphic relations as references for longer-term sea-level determinations. Inferences of Pliocene global sea-level heights or stability of Antarctic ice sheets therefore cannot be deciphered in the absence of an appropriate mantle dynamic reference frame.
Or: yet another reason why Hansen's radical views are wrong.

Note that sea level is still expected to rise should temperature increases resume, but that even the IPCC estimates this rise to be 12 inches by 2100...vs. the 30, 40, 50 feet or more the more radical viewpoints believe.

Ironic actually. One of the nails in the plate tectonics debate was actually similar: the occurrences of fossilized shells at levels far above present waterlines made the 'no plate tectonics' argument untenable, even apres le deluge.