According to some estimates, if sea levels rose one meter, Boston would lose 3% of it’s land surface, Washington DC a mere 1%. Tampa and Miami would lose 18% and 15% respectively. New Orleans would lose 91%.

A six meter rise would result in much larger losses. Norfolk, Virginia and Miami Florida would be essentially gone.

These estimates use the assumption that the sea level rises in those areas vertically, and the corresponding topographical level in the coastal city becomes the shoreline. They don’t account for the fact that the ocean does not work that way. (see Sea Level Rise…Extreme History, Uncertain Future.)The shore of the ocean normally consists of a relatively flat zone covered by sea (perhaps exposed ~2 times a day at low tide), a steeper zone where the sea intercepts the land (and generally goes up and down a certain amount with the tides) which was carved out by erosion, then inland, whatever topography would have been present prior to the incursion of the sea. The original shorline first contacted by the sea is gone, and the strandline has moved, or transgressed (that’s the term we use), some distance across the landscape. In a place like Miami, the sea may transgress many miles across relatively easily eroded sediment. In a place like Boston, filled land (which makes up a huge amount of that city’s land surface) might be easily eroded away, glacial sediments that make up much of the city’s substrate would erode fairly quickly. Rock conglomerates that make up much of the southern part of the city would erode slowly while weathered argilite underneath Cambridge would be eroded away quickly. The North Shore communities, sitting on hard rhyolite, would make nice islands for a long time. In other words, it would be complicated. Continue reading How much can the sea level go up with global warming and how fast will it happen? →