Saturday, December 10, 2011

Sea Level

New site, h/t WHT:

As with many climate impacts, the problem of sea level rise is a little more complicated than it appears at first blush. There is, of course, the problem of putting valuable real estate under water. Five million square kilometers of land lies within 10m of sea level; but it is not just any land. For thousands of years, boats have been the most efficient way to move goods; before the advent of railroads, automobiles, and airplanes, they were also by far the fastest. Hence huge numbers of people live at the water's edge. Today, about 37% of the world's people live within a 100km of the coast; by 2030, half the world's people will. About 500 million people currently live within 5m of sea level; those are the people whose homes are likely to be under water sometime between 40 and 400 years from now. There are 800 million people within 10m of sea level; they will probably have to move eventually as well.

But in addition to human settlements from small towns to great metropolises that must either by lost to the sea or protected via a huge and expensive system of dikes, there are additional consequences to sea level rise. One is erosion; higher seas mean the ocean takes bigger and bigger chunks of land away with the waves. This has been estimated at about 10% of rate of inundation -- so if we lose 5 million square km to rising seas, we might expect to lose 500,000 km^2 to erosion.

A more subtle problem is the infiltration of salt water deep inland.

 As the sea level rises, salt water filters into the aquifers, a problem exacerbated by over-pumping. In California, some regions have already been forced to inject fresh water into the aquifer on a regular basis to create a barrier to slow the infiltration of salt water into the aquifer.

An excellent report on sea level rise, its dangers, and the costs of adaptation, is here. The cost of the realistically expected sea level rise in this century alone is in the trillions. These estimates do not take into the loss of historic cities, the destruction of wetlands, corals, and wildlife, or the cost of conflicts over limited water or the resettlement of refugees.


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