By Tom Yulsman for Discover Magazine. View original post here.

Part of the problem comes from damning along the Mississippi, and construction of levees, which prevent sediment from flooding out into the wetlands like they once did. The result: As the mud of the marshes naturally sinks under its own weight, it is not being sufficiently replenished with new sediment. The net effect is subsidence.

This is exacerbated by canals dug for oil and gas exploration, which has allowed saltwater to intrude into freshwater marshes and kill them off.

The death of the protective marshes, along with subsidence, means the sea is coming up faster than anywhere else on Earth — an impact made even worse by strong hurricanes and other extreme storms in recent years.

The 2007 report from the Intergovernmental Panel Report on Climate Change put the global average rate of sea level rise at about 2 millimeters per year over the past century. More recently, research has shown that between 1993 and 2011, sea level actually rose about 60 percent faster than that – at a rate of 3.2 millimeters per year.

As temperatures continue to rise under the influence of greenhouse gases from human activities, that rate should increase even more. When that is taken into consideration, researchers expect sea level globally to be aboutthree feet higher in 2100, on average, than today.

But along the Louisiana coast, the new, unpublished NOAA report suggests sea level could come up by more than four feet, thanks to the fast rate at which the land is subsiding.

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