New research: Louisiana coast faces highest rate of sea-level rise worldwide

Stunning new data not yet publicly released shows Louisiana losing its battle with rising seas much more quickly than even the most pessimistic studies have predicted to date.

While state officials continue to argue over restoration projects to save the state’s sinking, crumbling coast, top researchers at the National Oceanic and Atmospheric Administration have concluded that Louisiana is in line for the highest rate of sea-level rise “on the planet.” * Indeed, the water is rising so fast that some coastal restoration projects could be obsolete before they are completed, the officials said.

NOAA’s Tim Osborn,** an 18-year veteran of Louisiana coastal surveys, and Steve Gill, senior scientist at the agency’s Center for Operational Oceanographic Products and Services, spelled out the grim reality in interviews with The Lens. When new data on the rate of coastal subsidence is married with updated projections of sea-level rise, the southeast corner of Louisiana looks likely to be under at least 4.3 feet of gulf water by the end of the century.



Port Fourchon experienced serious flooding from Hurricane Ike, which made landfall in Galveston, Texas in 2008. Scientists say such flooding will become more common, even in smaller storms, as the coast sinks and sea level rises.

That rate could swamp projects in the state’s current coastal Master Plan, which incorporated worst-case scenarios for relative sea-level rise calculated two years ago— which the new figures now make out-of-date. (The state’s estimates of sea-level rise and subsidence are listed on page 83 of the Master Plan.)

The state plan, while “valuable and thoughtful,” has a major flaw, Osborn said.

“The problem is it’s a master plan for the restoration and conservation of a landscape that is moving downward at a faster rate than we realized when the plan was constructed—a rate faster than any place else we are seeing in the world for such a large land area,” said Osborn, who will be a speaker Saturday at Tulane University’s Summit on Environmental Law and Policy.

“With all due respect,” he said, “they have projects designed to last 50 years at one level of relative sea-level rise, when they should be building projects that can function for several generations as sea level rises twice as high, if not higher.”

Garret Graves, head of the state Coastal Planning and Protection Authority, did not respond to a request for comment. But in an earlier interview he said the uncertainty of future rates of sea-level rise was one of the biggest challenges facing the plan. The planners, he said, typically have incorporated the then-current “worst case” scenarios for sea-level rise at those locations.

Graves also pointed out that the plan was structured to adapt to changing circumstances. The Coastal Planning and Protection Authority must submit an updated plan to the state Legislature for approval every five years.

Yet NOAA’s new figures, contained in draft reports currently under peer review, will present a challenge because the numbers have changed so drastically. Even heavily populated areas, such as New Orleans, appear to be sinking faster than expected, in fact even faster than some areas along the coast.

More precise tools show coast sinking faster than expected

Southeast Louisiana—with an average elevation just three feet above sea level—has long been considered one of the landscapes most threatened by global warming. That’s because the delta it’s built on – starved of river sediment and sliced by canals — is sinking at the same time that oceans are rising. The combination of those two forces is called relative sea-level rise, and its impact can be dramatic.

Scientists have come up with four scenarios of sea-level rise, ranging from .2 meters (8 inches) to 2 meters (about 6.5 feet). They're using the mid-range figure, about 4.5 feet, to make local projections of relative sea-level rise.

Scientists have come up with four scenarios of sea-level rise, ranging from .2 meters (8 inches) to 2 meters (about 6.5 feet). They're using the mid-range figure, about 4.5 feet, to make local projections of relative sea-level rise.

For example, tide-gauge measurements at Grand Isle, about 50 miles south of New Orleans, have shown an average annual sea-level rise over the past few decades of 9.24 millimeters (about one-third of an inch) while those at Key West, which has very little subsidence, read only 2.24 millimeters.

For decades coastal planners used that Grand Isle gauge as the benchmark for the worst case of local sea-level rise because it was one of the highest in the world. But as surveying crews began using more advanced instruments, they made a troubling discovery.

Readings at a distance inland were even worse than at Grand Isle. “For example,” Osborn said, “we have rates of 11.2 millimeters along the south shore of Lake Pontchartrain—the metro New Orleans area. And inside the city we have places with almost [a half-inch] per year.

“So when we looked at the averages we were getting inside the coast, we realized the current figure we should be using for [southeastern] Louisiana is 11.2 millimeters.”

The news got only more bleak when NOAA began using the new technologies to update past rates of local subsidence and then fed those numbers into studies projecting future rates.

“What we see is that the [southeast] Louisiana coast averaged three feet of relative sea-level rise the last century,” said NOAA’s Steve Gill.

Prepare for ‘at least four feet’ of sea-level rise

The draft report of the quadrennial National Climate Assessment, finished by federal agencies in December, showed a steady increase in sea-level rise through the end of the century. Gill said the increase was due to the continued increase in the two main contributors: thermal expansion of marine water volumes as oceans continue to warm, and an increase in the melting of land-based ice, such as glaciers and ice fields. That water eventually makes its way into the ocean, further increasing its volume.

The assessment provides four scenarios for global average sea-level rise through the end of the century, based on varying scenarios of warming and ice melt:

  • The first shows current trends holding steady, resulting in about an eight-inch rise globally.
  • The second, or intermediate increase, results in about 15 inches globally.
  • The third, or mid-range, shows about 4.5 feet.
  • The fourth, or worst case, shows about 6.5 feet globally.

The NOAA researchers said they use the mid-range scenario in making local projections.

Southeast Louisiana fares much worse in all four scenarios because “we now know the entire area is sinking faster than any coastal landscape its size on the planet,” Osborn said.

“When you combine those two factors, update the rates from what we’ve found with the most recent data—and that is data, not computer models or theories—then you see this area, southeast Louisiana, will experience the highest rate of sea-level rise anywhere on the planet by the end of the century,” Osborn said.

“We’re talking probably at least four feet if not five feet in some sections of this coast. That’s what people here need to be planning for.”

This NOAA chart shows the percentage of each parish that is projected to be below sea level in 2050 and 2100.


This NOAA chart shows the percentage of each parish that is projected to be below sea level in 2050 and 2100.

Osborn said he believes coastal Louisiana has a chance at survival because the Mississippi River carries the raw building material—sediment—in such huge quantities that projects could help some areas keep pace with the rising Gulf. But he stressed that the new figures mean current plans need to be amended to focus on the most vulnerable areas, and work must start soon.

“Our goal is to provide meaningful numbers that local planners can use as targets for what they need to prepare for and adapt to,” he said. “And what these numbers tell us is that we need to be planning for the reality that by the end of this century most of this coast will be converted to open water.

“What that tells us, in turn, is what we’ve already seen recently with [Hurricane] Isaac: Even a small storm will result in catastrophic flooding, and not just for people and businesses and infrastructure close to the coast.

“Based on the frequency of storms over the last century, we know we can expect 30 to 40 hurricanes or tropical storms to hit this area by the end of this century. Think of Isaac—not of Katrina—and add up the cost of that kind of destruction 30 or 40 times.

“During Isaac, Louisiana [Highway] 1 to Grand isle was almost impassable. It will be impassable in a few decades unless something is done. Look at what happened to Plaquemines Parish from Category 1 Isaac. More and worse will happen in the next few decades.”

Osborn stressed the new figures mean the state’s Master Plan should be adjusted to meet the larger, faster-approaching threat.

“People are already questioning the wisdom of spending huge sums to protect Louisiana,” he said. “The state needs to make sure they’re proposing plans that will last more than a few decades, that they aren’t asking for billions to build things that might be ineffective before they are even finished being built.”

*Correction: The original version of this story misstated the name of the National Oceanic and Atmospheric Administration.

**Osborn’s name was misspelled in the original version of this story. 

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About Bob Marshall

From 2013 to 2017, Bob Marshall covered environmental issues for The Lens, with a special focus on coastal restoration and wetlands. While at The Times-Picayune, his work chronicling the people, stories and issues of Louisiana’s wetlands was recognized with two Pulitzer Prizes and other awards. In 2012 Marshall was a member of the inaugural class inducted into the Loyola University School of Communications Den of Distinction.

  • WOW. But, nothing is going to be done on it’s causes. Not with this congress.

  • Much of this is being caused by those damned levees everyone is so proud of !

  • Frustrated Fan

    Terrific and terrifying article. So glad you are on the job.

  • WAKE UP!!!!! or be ready for no wake signs on your doorstep.
    And not just for a dumb ass driving too fast on a flooded street…
    If just 1/2 of this data passes muster, it’s now or never with our ecosystem eating itself to death.
    And all is hard to fight as a small Purple State (Red+ Blue= Purple)-
    They exploit our resources and treat us like 3/5ths of Citizen, but we make 1/3 of their energy.
    Yes 5 out of 4 of us are bad a fractions, but it’s snow up
    North today – what happens without Tap
    And I joke when I say lets turn it off until we get the same oil
    royalties as Texas, Alaska, and other States.

    but this data proves that’s on it’s way soon. Then what?
    What happened to this approach-
    Or I can jest and say- subsidence=succession…
    Our inalienable rights are have been and are being violated…
    Our way of life has been irreparably damaged building Suburbia, and continues be exploited by what I like to call Plasticonus Americonus.
    They got condos, and we got Macondo’d.
    I’m no expert- and know we lost big on court cases 1947and 1950,
    but if “you can sue a ham sandwich”- I say we sue them on every angle to cut the BS tape, give us our fare share, to hire our own oil and gas
    industry to immediately cut fresh water diversions, dredge, and do every fix we can NOW!!!

    Sorry for the ramble- I just needed to vent.

    Best From Freret,

    Andy Brott


  • I think the author needs to be more cautious with his projections before we frighten off an entire area. Can you really use the subsidence numbers and make accurate projections with that data? Could those extreme numbers, particularly in the NO area be due to longstanding Katrina waters accelerating the subsidence of the soil? If so, you can not project with those numbers because they will be skewed by that event. There is a finite amount of subsidence that can occur.

  • I know the subsidence levels in the reclaimed neighborhoods north of Robert E. Lee because I helped my father build a brick step at the two primary doors on Egret Street less than 20 years after the house was built. (A neighborhood engineer mocked my father for the number of pilings he put under that house. Someday it will be a favored spot to tie up and fish.) I think that the actual amount of land below sea level in Orleans Parish is exaggerated by including those neighboroods and New Orleans East. I argued that the East and St. Bernard should not be resettled after the Federal Flood, that we needed to retreat to a sustainable footprint in terms not of population but in what could be protected.

    There is no will in the United States to invest on the level required to due something about the problem (Sherwood Gagliano’s old bench mark of a project on the scale of the Interstate system or the Apollo program). There is not even sufficient will in Baton Rouge, as many reclamation projects will disrupt the salinity levels today’s coastal fishermen (especially oystermen) depend upon.

    And you left out one other critical factor in subsidence: removal of sub-surface oil deposits, which have helped accelerate events on a geological scale to a historical time scale.

  • Louise, see my comment before about subsidence in the filled land of Lake Vista, a good six inches in less than 20 years and before Katrina. And someone needs to build a Google Earth overlay from an older map of East Plaquemines and St. Bernard Parish, just so people can see how drastically that area has changed.

  • libertybelle2012

    Absolute fearmongering. There is no evidence that man is causing global warming or sea level rise. All these “experts” are radical environmental groups…including our current NOAA administrators. You would think the earth has never seen weather before. Wake up…this is one more attempt to separate you from your money and control every aspect of your lives.

  • wetlandscientist

    you are an idiot….why don’t you go on google earth timeline and see for yourself. or better yet back up you claim and go buy a bunch of land in southern louisiana, build a house and sit there and watch.

  • Steve Myers

    Please, let’s avoid name-calling and stick to a discussion of the issues.

  • jfreed27

    No evidence that you would recognize, you mean. Fun to play scientist. Now you can play doctor when you get very, very sick.

  • Chris McLindon

    Another great article Bob; I hope the rest of the science journalism community starts to follow your lead. There is no need for panic however, relative sea level rise is equal parts global eustatic rise and local subsidence. In south Louisiana subsidence is controlled by the same geologic forces that have been in play for millions of the years. The deep-rooted processes of crustal tectonics, faulting and salt movement are the reason that Mississippi River deposits are up to 10 miles thick in some places. Those forces are mainly in play along a portion of the coast called the “Terrebonne Trough”. The rapid rates of subsidence measured at Grand Isle are largely due to these deep-rooted mechanisms. Nearer to New Orleans the shallow forces in play are probably more significant. Compaction of organic marsh and swamp deposits causes most of the noticeable effects in the greater New Orleans area. These areas have subsided at a greater rate than those underlain by the natural levee deposits of the river and the buried barrier island deposits below the Gentilly and Metairie ridges.

    Most of the major population centers in south Louisiana are located on natural levee deposits from any of several older channels of the Mississippi River. They are likely to experience the lowest rates of relative sea level rise in the coming decades. The biggest problem we will face will be maintaining flood protection infrastructure. We have got to stop wasting money on coastal restoration projects that are located in the high subsidence areas. They are doomed to failure before they are ever constructed. We are going to need all the money we can get from the federal government to maintain our levees. If we continue to waste hundreds of millions of dollars on ill-fated restoration projects, at some point there will be no going back for more – when we will need it most.

  • Jack Wolf

    That Liberty Bell seems to have affected your ability to think. Pretty much all the scientists, the organizations, and the universities discuss it as currently happening, and indeed that is the case. The AAAS just put out a report that’s easy to read and that I think you will find enlightening: http://www.aaas.org/news/aaas-kicks-initiative-recognize-climate-change-risks

  • Jack Wolf

    It gets frustrating to see the world being destroyed, intentionally. And, it’s hard not to take that personally.

  • Jack Wolf

    Louise, look at the recent reports of ice loss from Greenland and Antarctica. If anything, the writer has understated the immediate danger from sea level rise. Furthermore, the scientists and their models have consistently under called the nature and timing of climate change impacts. Dr. Michael Manning said in his 2012 journal paper (and that was before the news of the ice disintegration): Harmonization of international, national, subnational, and local policies for the orderly resettlement of coastal populations should begin now. This will become a chronic condition involving very large numbers of people. Improved and coordinated policies are needed for refugee services and related issues of migration and integration as well as planning for land use change and infrastructure development.

  • Jack Wolf

    Maybe in the past, but not anymore. Not with abrupt climate change.

  • davemills555

    This article reminds me of Florida, where it’s really fun to watch the current governor squirm as we see his idelogical do-nothing position on the environment running counter to proven science. Five climate scientists recently warned him that a steadily rising ocean threatens Florida’s future. These five climate experts urged him to have a “leadership” moment regarding developing solar energy and other clean power sources. After listening to these five climate experts, the governor refused to take questions and offered no comment. In my opinion, Floridians need a new governor. Maybe soon, they will elect a governor that believes in climate science. Sadly, with the polar ice caps melting at a record rate, it just might be too late for Florida’s populated coastline.

  • geezer117

    All along our coasts, tide gauges have been measuring sea levels for nearly two centuries. The rate of actual rise in sea level has been a constant 7 inches per century, and the rate has not fluctuated at all, even during the highest recent decades of manmade Carbon Dioxide. There are different rates of land subsidence. It is deliberate political misinformation to choose the term “relative sea level rise” to describe what is in fact land subsidence. Just another proof that one can’t trust politicized scientists.

  • nickelndime

    Thanks geezer117 for the comment. A couple of comments were made “2 years ago.” That can’t be right. Or r r r were the comments made in advance of the article? We may have at least two real psychics out there! Who needs “science”?!