The future of Gulf of Mexico fisheries got a grim forecast this week when the National Oceanic and Atmospheric Administration reported the stunning finding that its latest data indicated southeast Louisiana would be inundated with more than four feet of sea level rise by the end of the century – the highest level “on the planet.” The average elevation of that landscape is about three feet.

That area encompasses the great estuary of the Mississippi River, which is responsible for much of the fisheries production in the Gulf. If its marshes are flooded, production will plummet. Of course, the threat to many cities is also dire.

The new revelations are not so much the result of upward forecasts of sea level rise contained in the draft of the new National Climate Assessment, which measures the rise of oceans based on thermal expansion and increased volume due to melting ice fields and glaciers. That trend was expected.

Instead, most of the dramatic increase — more than a foot above the previous high-level predictions – for the Mississippi delta comes from more accurate measurements of its rate of subsidence.

NOAA researchers said Louisiana’s southeastern coast is sinking at the fastest rate of any other large coastal landscape in the world. One of the most significant, and startling, findings was that the subsidence rate inside the coastline was actually higher than that of the state’s barrier islands, long thought to have the world’s highest rate of relative sea level rise, which is calculated when subsidence is combined with sea level rise.

The new findings pose serious challenges to the state Master Plan for restoring its coast, a 40-year, $50 billion project which authorities said could actually have the state building more land than it was losing by 2050. However, that prediction was based on the previous rates of predicted relative sea level rise.