Thursday, July 2, 2009

It's Worse Than You Know

One of my favorite movies, Joss Whedon's "Serenity," has a little bit of dialogue that is quite appropriate to some climate change and Mississippi River news that came out this past week. The movie's villain and hero are having a conversation, and the villain says that the situation is "worse than you know." To which our hero replies, "It usually is."

Which is a bit like the cover story published in the July 1 edition of the NewScientist: "Sea level rise: It's worse than we thought." To quote the article, "The good news is that some of the scarier scenarios, such as a sudden collapse of the Greenland ice sheet, now appear less likely. The bad news is that there is a growing consensus that the IPCC (Intergovernmental Panel on Climate Change) estimates are wildly optimistic . . . The oceans are already rising. Global average sea level rose about 17 centimetres in the 20th century, and the rate of rise is increasing."

What does this have to do with the Mississippi River region you might ask. Well, beside the typical answer that "all things are connected," and that a crisis in one region will have repercussions in others, there is the article just published last Sunday in ScienceNews, the magazine for the Society of Science and the Public. That article, "Losing Louisiana," says that engineering attempts to save a sinking Louisiana delta by allowing sediment-laden Mississippi River water to overflow the River channel into the delta region will fail, because the River no longer carries enough sediment for those efforts to succeed. There are dams on the River now and farther upstream on many of its tributaries, too - each dam trapping tons of sediment that at one time reached the delta and replenished its wetlands.

The ScienceNews article cites an analysis by Michael Blum and Harry Roberts, published in the June 26 online issue of Nature Geoscience (free registration required), in which the authors estimate that between 2000 and 2100, the combined effects of subsidence and sea-level rise will swamp as much as 13,500 square kilometers — about 10 percent - of the area of Louisiana.

Blum and Roberts estimate that, compared to times when the Mississippi River was free-flowing, today only about half of the River sediments reach the delta region. Therefore, diverting sediment-laden Mississippi River water into wetlands at the head of the delta will only prevent about 900 square kilometers of land from sinking below sea level over the next 100 years.

The scientists conclude their article by saying, "Our calculations of sediment mass balance represent a conservative first-order assessment because we use modest subsidence rates, conservative sea-level rise estimates, optimistic sediment supplies and an optimistic timeline for implementation of large-scale diversions."

In other words, it may be "worse than you know." - Mark Gorman

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