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Wednesday, June 19, 2019



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It’s sinking land AND climate change

It’s sinking land AND climate change

Since 1947, a gauge run by the National Oceanic and Atmospheric Administration has captured the Gulf of Mexico’s steady rise at Grand Isle.

About 70 miles to the east, data collected at Eugene Island between 1939 and 1974 showed a similar trend: the water is rising at a rate of about 3 feet every century. It’s the highest rate of any area along the Gulf.

In the 71 years of data collection at Grand Isle, NOAA found that the relative sea level rise has equated to about 9.08 millimeters, a little over a third of an inch, each year.

While a centimeter may not sound like much, NOAA scientist Tim Osborn said the effect is amplified in parts of Louisiana like Terrebonne Parish, where much of the land is only a few feet above sea level. Some areas in both Terrebonne and Lafourche are below sea level, relying on levees to keep the water out.

“If you’re living at 15, 20, 80 feet above sea level, then you’re not really bothered by this,” he said. “Since 80 percent of Terrebonne is at 2 feet or less, then you’re losing a lot.”

Only about 8 percent of Terrebonne is inhabitable; the rest is water and marsh. Each millimeter reduces the amount of livable land.

Two factors contribute to the water’s approach: global sea level rise and sinking land, or subsidence.

Along the Gulf, 2-3 millimeters of the relative sea level rise is due to the introduction of more water into the ocean through climate change, federal scientists say. Thanks to the composition of Louisiana’s coast, subsidence is occurring at a higher rate than anywhere else in the United States.

Osborn said his agency looks at the gauge in Pensacola, Florida, which sits on limestone, as an example of an area only facing climate change. Seas there are rising by about 2.4 millimeters per year.

Alex Kolker, a scientist at the Louisiana Universities Marine Consortium’s research center in Cocodrie, said about one-third of the relative sea level rise in coastal Louisiana is due to climate change, while the other two-thirds are from sinking.

Some areas of Louisiana, such as Baton Rouge, have a lower subsidence rate than Terrebonne based on factors such as how much soft sediment there is, the amount of oil and gas being pulled out of the ground and how much has been built up on marsh and old swamps.

Kolker described 3 feet of expected sea level rise per century as the difference between having water in your shoes or wading through water up to your midsection.

Rather than using the term climate change to describe what’s happening to the coast, Kolker said he prefers the term “coastal change.”

“Some of the biggest factors have been other factors than climate change,” he said.

But global sea levels are expected to become more of a concern over the next few decades.

“It’s the component of coastal change that’s likely to change the most in the coming years,” Kolker said.

Scientists expect that the rate of global sea level rise will accelerate to match Louisiana’s subsidence rate at 1 centimeter per year by the middle of the century, he said.

LUMCON scientist Brian Roberts and Osborn noted that south Louisiana residents have already begin to adapt.

Roberts pointed to the development of Morganza-to-the-Gulf, a system of levees, locks and floodgates that helps protect most of Terrebonne and part of Lafourche from storms surges. Osborn noted that many Plaquemines Parish residents have migrated to nearby Jefferson Parish to escape flooding and now commute to and from their home community for work.

“This is important to people,” he said. “And that’s something we need to think about as we move forward.”

 

-- Daily Comet Staff Writer Halle Parker can be reached at hparker@houmatoday.com or 857-2204. Follow her on Twitter @_thehalparker.