In Other Sea Level News....

Here's an interesting paper that raises an issue many people haven't thought about: how much water are dams holding back from the sea?

Humans have been building a lot of dams over the last century or so, holding back water that would otherwise be going to the sea (and raising sea levels beyond what's measured).

How much? The authors calculate that dams hold back about 10,800 km3 from running into the sea. As a means of comparison, that's just a bit less than is in Lake Superior (12,000 km3), the world's 3rd largest freshwater lake. (If a cube, it would be 14 miles on each side.)

This dammed water has reduced sea level by 3.0 cm. But, here's where it gets interesting: the weight of the water behind dams lowers land levels near it, which in effect raises the local sea level, by about 0.2 mm/yr, or about 10%.

Source: Fiedler, J. W., and C. P. Conrad, Spatial variability of sea level rise due to water impoundment behind dams, Geophys. Res. Lett. 37, L12603, doi:10.1029/2010GL043462.