The Intergovernmental Panel on Climate Change, a worldwide consortium of scientists studying the issue, has increased its estimate of future sea level rise by 60 percent over its previous report.

When the state unveiled the the first detailed Coastal Master Plan in 2012, a selling point for the 50-year $50-billion effort was that it would be building more wetlands than the rising Gulf of Mexico would be swallowing by 2061.

But all along, some noted researchers suggested the plan’s ambitious goal to save large sections of the southeastern coast would be overmatched by its two biggest obstacles: The rapidly rising Gulf and a coastal landscape built on a sediment starved delta sinking at one of the fastest rates on the planet.

Now, as the state is spending money to engineer and plan the costly sediment diversions at the center of the effort, two developments are giving those old doubts new prominence:

Any change to the science supporting Louisiana’s coastal plan is crucial because the continuously sinking coast places a deadline on action.

If the state waits too long to act, most of the coast will have been swallowed by the Gulf of Mexico, resulting in the loss or relocation of the communities and vital industrial hubs it aims to save. But if it errs in selecting a strategy and projects,  it might then lack the money to begin new work.

The state recognized the challenges of the many uncertainties facing its goals by requiring the Coastal Protection and Restoration Authority to update the plan every five years using the latest information. And since 2012, a suite of new research by the state and the U.S. Army Corps of Engineers has provided up-to-date information, allowing computer models to more accurately project how much land-building potential the river and other sources hold.

But during that same time span, new research has also increased the size of the challenges.

In simplest terms, the holes the river now must fill with its sediment are projected to be much deeper and wider in the decades ahead than was expected even two years ago.

So as the coastal authority prepares the 2017 edition of the plan, new questions are being asked about some of the fundamentals that have long guided the effort.

Does the river carry enough sediment to fill what are now projected the deepening holes outside the levees?

Should the state be planning  for the worst-case  scenarios of subsidence and sea level rise and be looking ahead for 100 years instead of 50?

Is it worth investing $90 billion in wetlands that might be gone 40 years later?

We’ll look at each of these questions over the next three days.

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...