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Location: St. Louis, Missouri, United States

Tuesday, June 21, 2011

A 2000 Year Study of Sea Level Rise in North Carolina

Timothy Birdnow

Michael Mann is up to his old tricks; he's co-authored a study that supposedly shows sea level rise has greatly accelerated in the industrial era.

Uh, sure, Mike.

This study, which reconstructs the last 2000 years, only looked at the North Carolina coast. Now, anyone who bothers to look at North Carolina would know that it is a swampy, low water region with a chain of islands (the Outer Banks) and considerable port activity. I suppose it never occured to Mann et al that there has been, uh, dredging going on since these coastal regions were settled, and perhaps sea level rise is attributable to clearer coastal bottoms? Dredging and control of river flooding means less silt backing up on the shore. Can Mann and company determine how much of an effect this has had on apparent sea level rise in North Carolina?

This is true in Louisiana, where low lying wetlands have been disappearing. For instance:

"Human disturbance has had a massive impact on the balance of wetland growth and decline. Since the colonization of America, over half of the original wetlands have been lost. In modern times and with the increase in available technology, this loss has accelerated geometrically. In the past 100 years, Louisiana has lost 20% of its wetlands, representing an acceleration of 10 times the natural rate.

The main forms of human disturbance are the river-control structures such as dams and levees, the dredging of canals, and draining and filling. Beginning in the 1920’s, large scale river-control structures, such as the Old River Control Structure, which diverts 30% of the Mississippi Rover water into the Atchafalaya River system, were built to ease flooding problems along the banks. These control structures led to a dramatic decrease in the sedimentary load which reached the mouth of the river and formed the basis of new coastal land.

The construction of levees similarly affected coastal land. A large part of the sediment gathered by existing marshes is accumulated during seasonal flooding. Flood overtopping and overbank sedimentation, both vital to the survival of existing marshes, were dramatically reduced as large areas ceased to be flooded. River water also helped to reduce marsh salinity and provide nutrients, and its loss has resulted in the breakup and dispersal of large amounts of nutrient-starved marshlands.

Canal dredging has had one of the most dramatic effects on wetland growth and regeneration. In addition to directly destroying marshes in the path of the canal, the plants are unable to recolonize, and thus the marsh is unable to regenerate itself. Once canals are dredged, most grow larger as the sustainable areas of marsh subsequently decrease. The largest and most destructive example of this dredging is the Mississippi River Gulf Outlet (MRGO). Created in the 1960’s to facilitate the passage of ships to the Gulf of Mexico, the canal destroyed over 23,000 acres of wetland. The MRGO has now grown to 2 ½ times its original size and costs the government $7.6 million a year to maintain. Experts say that canals now account for 6.8% of Louisiana’s wetland area."

End excerpt.

This phonomenon is well-documented along the Louisiana coast, so I used it as a case study, but it clearly occurs along the North Carolina coast as well.

Has Mann and company considered that the Little Ice Age locked up a good deal of sea water and that the modern warming period is seeing the release of that locked up water?

It's also interesting to note that the article in Der Spiegle says this rise correlates with the industrial era; what does that mean? When did it start, before or after the strong rise in carbon dioxide emissions? If before 1900 it would be a technically correct statement but utterly meaningless, because this rise cannot be attributable to industrial emissions.

This is just another example of "Mike's nature trick", but it will be seized on by the uninformed and the partisan.

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