A sobering new study using methods that allowed scientists to "time travel" into the future finds that three-quarters or more of Louisiana’s remaining coastal wetlands could be drowning by 2070 as climate change fuels rising seas.

The study by a trio of Tulane scientists puts into new focus the increased dangers Louisiana faces as temperatures warm. Sea-level rise linked to climate change is adding to the list of risks to the state’s coast, which has already lost land the size of Delaware over the past century.

Published on Thursday in Nature Communications, a peer-reviewed scientific journal, the study was authored by Guandong Li, Torbjorn Tornqvist and Sonke Dangendorf. Li is a doctoral student at Tulane, studying under Tornqvist, whose previous work on Louisiana’s coast has shed new light on the crisis. Dangendorf is a widely recognized expert on sea levels.

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The land where an earlier incarnation of Campo's Marina near Shell Beach and Lake Borgne once stood is now nothing but a patchwork of drowning marsh grass.?(Flight courtesy of SouthWings)

While Louisianans are largely familiar with the state’s coastal challenges, set in motion by various manmade factors, the authors use real-world observations to describe how the situation is set to badly worsen for the state's roughly 5,800 square miles of remaining coastal wetlands – an area slightly larger than the state of Connecticut. The state has already experienced the world’s highest rate of wetland loss, but rapidly rising seas are leading to even more extreme projections.

If the world continues on the climate path it is now following, around 75% of Louisiana’s coastal wetlands could be “drowning” by 2070, said Li, the study’s lead author. That means they will be unable to keep up with the combined rate of persistently rising seas and subsiding land. Some may already be lost by then, while others will be in the process of slipping under the waves for good.

“It basically means that they're in serious deficit,” Tornqvist said in a joint interview with Li. “In Louisiana, that means that you may have a couple of decades left, but it's not going to be more than that.”

If seas rise annually at 7 millimeters or more on a consistent basis – the world’s current trajectory by 2070 – “well, we know that the game is over, basically,” he said.

The study does not take into account future coastal restoration projects, including large-scale efforts like river diversions. But while those are important to stave off the worst for as long as possible, they will have relatively small-scale, localized effects, Tornqvist said.

The only way to truly fend off widespread collapse for as long as possible is to reduce greenhouse gas emissions, which are driving climate change, he and Li note. Warming temperatures melt glaciers and cause water itself to expand, resulting in rising seas.

Because of its petrochemical industries, Louisiana is among the nation’s biggest producers of greenhouse gases. Gov. Jeff Landry has made it clear he wants to expand those industries as well as oil and gas production.

While Louisiana’s emissions are small on a global scale, the state should still do its part to reduce them given how severely it is threatened by climate change, scientists like Tornqvist say.

The state's Coastal Protection and Restoration Authority has also projected concerning conclusions on land loss in its coastal master plan, though the new study is unique in how it uses a recent real-world example of seas rising. The authority said the new findings "are not inconsistent with our higher sea level rise projections without further restoration."

"The rapid sea level rise in the Gulf over the past decade has given us an opportunity to better study how wetlands respond under these conditions, which is very important as we look 30 and 50 years in the future," the authority said in a statement, adding that "key restoration projects have the ability to mitigate some of this loss."

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The New Orleans skyline, seen here from Chalmette, is perilously close to the eroding wetlands that once protected the city.

Seeing the?future

What allowed the authors to reach their conclusions is an unusual amount of sea level rise in the Gulf of Mexico over the past decade or so – roughly 10 millimeters per year along Louisiana, not taking into account the effect of sinking land, which adds to that number. While those rapid rates are believed to be in large part due to temporary conditions, they provide a glimpse of the future later this century, when sea level rise linked to climate change gains pace and becomes persistent, Li explained.

Using 253 monitoring sites across the coast, the study looks at how wetlands responded to the rising water – and the conclusions were not good. It found that 87% of the sites are not able to keep up.

The study found that the higher waters did not bring with them sufficient sediment to replenish the wetlands it washes over and allow them to maintain pace with the changes.

One finding may come as a surprise. The study says that, initially, some of the most vulnerable wetlands are in the interior of marshes, particularly those in the southwestern part of the state, possibly because of a severe lack of sediment reaching them.

The outer edges may last longer, at least in certain locations, though they, too, will face disappearance as the erosion, subsidence and rising seas continue to take their toll in the decades and centuries ahead.

‘More time to prepare’

The study helps put in perspective the dramatic consequences that will confront coastal Louisiana. While there is widespread agreement that the state’s coastal restoration efforts are vital, choices will have to be made about what can be saved.

The sheer scale of the problem is the main reason, but there are more practical challenges as well. For one, the state’s coastal agency will soon see a sharp drop in money available for its projects since funds related to settlements from the 2010 BP spill expire in 2032.

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A barrier surrounds Fort Proctor, which was originally build on land in Shell Beach, La., Tuesday, July 18, 2023. (Photo by Sophia Germer, NOLA.com, The Times-Picayune)

Still, coastal advocates repeatedly stress that giving up is not an option since the state will need as much time as possible to adapt. Meeting greenhouse gas reduction goals to fend off the worst projections of rising seas will also be vital, they say.

The international treaty on climate change known as the Paris Agreement aims to keep temperatures from rising 2 degrees Celsius (3.6 Fahrenheit) above pre-industrial levels, while encouraging 1.5 degrees as a goal. The world has already temporarily surpassed the 1.5-degree goal.

The new study says that the “widespread collapse” of coastal wetlands by 2070 or earlier “may not be entirely avoidable.”

But, it says, “climate mitigation along with major restoration efforts by means of sediment diversions could delay wetland drowning and allow for more time to prepare for this large-scale coastal transformation.”

This story was updated on Feb. 16 with a response from the state's Coastal Protection and Restoration Authority.

Email Mike Smith at msmith@theadvocate.com or follow him on Twitter, @MikeJSmith504. His work is supported with a grant from the Walton Family Foundation and administered by the Society of Environmental Journalists.

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