Over the past 80 years, at least 2,000 square miles of southeastern Louisiana's coastline have dropped off into the Gulf of Mexico—the equivalent of a football field-sized plot of land being swept away each hour, Scientific American reports. Unless the state takes action, 1,750 more square miles could be lost over the next half-century, and New Orleans could be stranded on a thin strip of land in the Gulf by the year 2085, ProPublica reports. While Louisiana does have a "master plan" to take on this problem, it is unprecedented in scope. Scientists have to factor in everything from how much sediment they can extract from the Mississippi River and future sea-level rise to how to accomplish all this with minimal impact to the energy, shipping, and fishing industries.
Money's an issue, too: Congress hasn't ponied up much cash, even though half of US oil and gas refineries and pipelines are in the threatened region. Should the increasingly vulnerable port of New Orleans be overrun by tropical storms, a shutdown could hurt our economy to the tune of $300 million a day, ProPublica notes. So far there are two viable proposals: pumping sand into the wetlands or bringing in sediment-filled freshwater, which more closely resembles the natural delta-building process but is more expensive upfront and takes longer (and nothing like it has never been done before). "We'll have to start … on a small scale, and there will be missteps along the way," a coastal geologist tells ProPublica. "But we have to succeed, because this, really, is our only hope." (The Pacific islands of Kiribati are slowly sinking as well.)