A new study says Louisiana’s coast cannot be saved.
Researchers looked at how the marshes have survived over thousands of years and concluded that they are past a major tipping point and sea level rise will eventually wash the entire coast away.
The study, published today in Science Advances, found that marshes can survive a certain amount of relative sea level rise — about a tenth of an inch per year. Sea levels are currently rising 1 to 2 inches a year in Louisiana due to climate change and subsidence.
“Previous investigations have suggested that marshes can keep up with rates of sea-level rise as high as half an inch per year, but those studies were based on observations over very short time windows, typically a few decades or less,” said Torbjörn Törnqvist, Lead researcher and Tulane University earth and environmental science professor.
He said officials have perhaps been too optimistic: “Unfortunately we have already reached the tipping point for marsh drowning in Louisiana. There is no way back anymore.”
Despite the state’s best efforts to restore and protect the coast, he said that given the present-day rate of global sea-level rise, remaining marshes in the Mississippi Delta are likely to drown.
Törnqvist and a team of scientists took 355 sediment core samples across the coast over several decades and examined geological records spanning 8,500 years, making it the most comprehensive study of its kind.
It is well documented that more than 2,000 square miles of Louisiana’s coastal wetlands have been lost over the past century due to subsidence and erosion, but it has been challenging for researchers to predict the fate of the remaining 6,000 square miles.
The state has a $50 billion Coastal Master Plan aimed at curbing land loss and rebuilding land, but officials have acknowledged that they cannot rebuild what’s been lost or stop further erosion. This includes plans for two major Mississippi River sediment diversions south of New Orleans. Törnqvist said the window of opportunity for these actions to be effective is rapidly closing.
The loss of the coast is inevitable, he said, but drastically curbing greenhouse gas emissions to prevent sea-level rise would slow land loss so that the coast doesn’t wash away in a matter of decades.