The posting talks about flooding from a variety of causes, including storm surge. 8 meters is roughly the level of the record storm surges estimated for Katrina, though they don’t know for sure because many of the tidal gauges were destroyed. See this NOAA article for more info.

I don’t know where you got the 10 cm/century figure for sea level rise, but it’s not correct. Measured rates of sea level rise using the TOPEX satellites indicate a rate of about 2-3 mm/year, and as the earth gets warmer, this rate is expected to accelerate by as much as 2-5 times due to the time lag between the atmosphere warming and the deep oceans. The most recent IPCC report on climate change puts the maximum sea level rise by 2100 at about 80 cm. But this report has been criticized because it hasn’t taken the latest data on sea level rise factors into account, like increased melting rates and ice flow in both Greenland and Antarctica. Over the past 50 years, predictions of future sea level rise have always underestimated the actual numbers.

Then there are the very low probability events, like the melting of the entire Greenland ice cap (which adds about 6.5 meters), and the collapse of the west Antarctic ice shelf (another 6 meters or so). These are highly unlikely, but not impossible; combine these with the factors mentioned above, and 8 meters actually looks pretty good. Of course, then you get to add an additional possible 8 meters of rise from a storm surge on top of that. Global warming may (or may not) increase the intensity and number of hurricanes.

8 meters of sea level rise would take 8,000 years using global average sea level rise (10 cm / century), and 2,600+ years in the Chesapeake region (.21 cm/year land subsidence + global sea level rise). Of course we would expect large changes in sea level over time scales that long; sea level was ~120 meters lower at the peak of the Wisconsin Ice Age ~15,000 years ago.