Why Is The Sea Level Rise Higher In The Southeast Than In Other Parts Of The US? – CleanTechnica

Sign up for daily news updates from CleanTechnica on email. Or follow us on Google News!

---

Did you know that the first water level observing stations were established in the 1850s? Even back then sea level rise was important to monitor.

Alexander Dallas Bache, second superintendent of the coast survey, explained in 1854, “It seems a very simple task to make correct tidal observations; but in my experience, I have found no observations which require such constant care and attention.”

A vertical staff in the water with a linear measure was replaced with a self-registering tide gauge by the late 1800s and used until the 1960s. These calculations are one of the most critical pieces of oceanographic data used to protect life, property, and the environment. Accurate data about the ever-changing US water levels provides the foundation for coastal activities from navigation to engineering to preservation: for navigating harbors and channels, predicting the best time for fishing, and fostering trade.

Today, the National Oceanic and Atmospheric Administration (NOAA) has a network of 210 long-term, continuously operating water level stations throughout the US and its territories. Its tide gauges are outfitted with backup sensors, satellite communications, and a version of GPS that allows precise measurement of the gauge height from a network of satellites around the globe.

The Fort Pulaski tide gauge is one example of the NOAA instrumentation. Located 15 miles east of Savannah, Georgia, for 90 years, this station has returned a steady stream of data to scientists, locals, and ship captains. It has assisted them as they assessed ocean rhythms and stayed clear of low tide hazards. The Fort Pulaski tide gauge has recorded approximately 10 inches of sea level rise since 1935 — but since 2010, the sea level at the Fort Pulaski gauge has risen by more than 7 inches. This makes it one of the fastest rates in the country.

Similar spikes are affecting the entire US Southeast coastline. Is this exponential southern sea level rise a harbinger of things to come in other coastal regions?

For Fort Pulaski, sea level rise is a serious threat, according to the US National Park Service — it could see 61 more high tide flood days per year by the 2050s.

• Sea level rise results in the loss of land, including critical terrestrial and freshwater habitats and archaeological sites.
• Sea level rise is causing a rising groundwater table, which means more “sunny day flooding” as the land becomes saturated.
• Saltwater intrusion into freshwater sources will contaminate drinking water.
• More flooding, especially saltwater flooding, will have unknown effects on artifacts buried in archaeology sites, causing the artifacts like those from shipwrecks to degrade faster and needing more conservation treatment once excavated.
• Climate change effects harm the park’s infrastructure, so, without basics like its bridge, roads, and bathrooms, citizens may not be able to visit Fort Pulaski in the future.

Towns and cities near Fort Pulaski are doing what they can to manage sea level rise by shoring up beaches, reconstructing stormwater systems, and anticipating a move of structures to eventual higher ground as the waters approach. Rising sea levels in the Southeast like those around Fort Pulaski may be unveiling a scenario of what’s ahead for the rest of the US and the world.

Why is the US South Experiencing Such Dramatic Sea Level Rise?

A team at the Washington Post analyzed 127 tidal gauges over a duration of 14 years. The assembled decades of data “form a long, undulating wave — representing the fluctuations of high tides and low, the natural rhythms of a coastline thousands of years old.” Yet the deep dive also shows “a new, troubling development.”

Hidden behind the ups and downs of the tides is a “steadily rising trend:” sea levels in the US South have risen twice as fast as the global average.

A 2023 Nature Communications article supports the Post‘s findings. The rates in the south, including the entire Southeast Atlantic Coast of the US and in the Gulf of Mexico, are on average 2–3 times higher than their northern counterparts. The rates are all significantly different from a long-term correlated random process plus linear trend since the mid-2000s.

Due to a complex set of factors, water levels are not rising at the same speed everywhere. A particular set of factors has made the US South particularly vulnerable.

Ice is melting in Greenland and Antarctica: Multiple possible drivers for the recent acceleration south are dominated by increased mass loss from the Greenland and Antarctic ice sheets. Meltwaters spill into the ocean and raise global sea levels everywhere. The coastlines farthest from the ice sheets are hit hardest because the enormous ice sheets exert a gravitational pull on the ocean. Sea levels close to the ice sheet fall, and sea levels farther away rise.

Land shifts: Everywhere in the world land is shifting. It happens because of the continuous movement of giant tectonic plates — which are slowly rebounding from the weight of glaciers that laid atop them tens of thousands of years ago. Locally pumped groundwater used for human consumption or for irrigating crops increase land shifts — withdrawing water from an aquifer creates a vacuum. In the Southeast, the land is sinking by about 0.6 inches per decade — which compounds the impact of rising seas.

Warmer water than ever: A warming planet returns 90% of the added heat into the ocean, and higher heat expands ocean waters levels. Those temperature gains aren’t distributed evenly. Some areas get hotter faster than others, and the surging currents wandering across the globe can carry warm water from one place to the next. Deep ocean waters are particularly devastating: as they expand, they cause sea levels to rise out in the open ocean. That expanded water then surges onto the coasts, spiking sea levels along beaches and shorelines. For the US South, the waters of the Gulf Stream and the Gulf of Mexico are warming faster than other parts of the Atlantic, boosting sea level heights.

Final Thoughts

The ocean constantly exchanges mass and energy with other components of the climate system. Winds drive mixing, waves, and currents that move water around in the ocean. These are sterodynamic sea level changes — they arise from changes in the ocean’s circulation (currents) and its climate (temperature and saltiness). Together, these exchanges cause differences in seawater density and mass between regions all across the global ocean. Beyond Cape Hatteras, this acceleration extends into the North Atlantic and the Caribbean Sea.

Curious about what your own coastal region looks like in relation to sea level rise? NOAA’s Office of Coastal Management has a web mapping tool to visualize community-level impacts from coastal flooding or sea level rise (up to 10 feet above average high tides). Photo simulations of how future flooding might impact local landmarks are also provided, as well as data related to water depth, connectivity, flood frequency, socio-economic vulnerability, wetland loss and migration, and mapping confidence.

The purpose of this viewer is to provide a preliminary look at sea level rise and coastal flooding impacts. This screening-level tool uses the highest accuracy elevation data sets available at the time maps were produced. The depictions in your coastal area may be startling.