Miami and New Orleans face greater sea-level threat than already feared

Coastal cities in the southern US, including Miami, Houston and New Orleans, are in even greater peril from sea-level rise than scientists already feared, according to new analysis.

What experts are calling a dramatic surge in ocean levels has taken place along the US south-eastern and Gulf of Mexico coastline since 2010, one study suggests, an increase of almost 5in (12.7cm).

That “burst”, more than double the global average of 0.17in (0.44cm) per year, is fueling ever more powerful cyclones, including Hurricane Ian, which struck Florida in September and caused more than $113bn of damage – the state’s costliest natural disaster and the third most expensive storm in US history, according to the National Oceanic and Atmospheric Administration (Noaa).

The University of Arizona study, published in the Journal of Climate and reported on Monday by the Washington Post, provides an alarming new assessment of a key ingredient of the escalating climate emergency, particularly in popular but vulnerable areas of the US where millions of people live.

Existing projections by Nasa show a sea-level rise up to 12in (30cm) by the middle of the century, with longer-range forecasts even more dire.

The Gulf region from Texas to Florida, and southern Atlantic seaboard will see most of the change, the agency says.

“The entire south-east coast and the Gulf Coast is feeling the impact of the sea-level rise acceleration,” the study’s author Jianjun Yin, professor of geosciences at the University of Arizona, told the Post.

“It turns out that the water level associated with Hurricane Ian was the highest on record due to the combined effect of sea-level rise and storm surge.”

The threat from rising oceans hangs over numerous centers of heavy population located on, or close to the coast. Miami, and Miami Beach, cities often cited as ground zero for the climate emergency, frequently see flooding during high tides. Property insurance rates throughout Florida, which Noaa says has experienced more than 40% of all US hurricane strikes, have soared in recent years.

The two most expensive hurricanes in US history, Katrina in 2005 and Harvey in 2017, ravaged New Orleans, Louisiana, and Houston, Texas, respectively,

Earlier this month, the Guardian carried an extract from a new book about how Charleston, South Carolina, is facing a “perfect storm” of rising sea levels and racism that leaves the city, in the view of many observers, living on borrowed time.

“What is likely to happen in Charleston is likely, absent a substantial shift in attitude, to happen in many other coastal cities around the globe,” wrote Susan Crawford, author of Charleston: Race, Water, and the Coming Storm.

The Post reported on a second study, published on Monday on nature.com, effectively mirroring the finding of the Arizona analysis that an “acceleration” of sea-level rise was under way.

Researchers at Tulane University, New Orleans, also note that the increase in the Gulf and south-eastern region is greater than the global average, a surge of greater than 0.4in per year they say is “unprecedented in at least 120 years”.

The study, which says the rise is “amplified by internal climate variabilities”, cites storms such as Katrina, and Hurricane Sandy in 2012, that “illustrate that any further increases in the rate of MSL [mean sea-level] rise, particularly rapid ones, threaten the national security of the US and hamper timely adaptation measures.”

Human activity in the Gulf region, which the researchers refer to as “vertical land motion” (VLM), has played a role, the study continues.

“It is well known that tide gauges in the Gulf of Mexico are subject to significant nonlinear VLM, likely related to oil, gas, or groundwater withdrawal. These nonlinear changes appear predominantly along the western portions of the US Gulf coast (Louisiana and Texas),” it says.