A Surge In Sea Level Rise Threatens Southern States

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I read a comment recently from a CleanTechnica reader who said that sea level rise happens uniformly all around the globe. That seems perfectly logical. If you have a bath tub full of water, the surface level is the same at both ends. Pour in a bucket of water and the surface quickly adjust to the increased volume. Once again, the level is the same at both ends of the tub.

However, when talking about oceans, we are talking about distances of tens of thousands of miles and trillions upon trillions of cubic feet of water. In fact, according to NOAA, there are over 321 million cubic miles of water in all the oceans of the world. That is a lot of water and it does not all slosh simultaneously from one side of the Earth to the other twice a day as the tides rise and fall.  As a result, there are distinct differences in the height of the ocean, depending on where you happen to be standing when you take your measurements.

A recent article by the Washington Post highlights a disturbing trend. Sea levels in the Gulf of Mexico have risen by six inches or more in the past 10 years — a far faster rate of rise than anyone in the scientific community expected. Most oceanographers expected that amount of change would not happen until the end of this century and even then, only if the Earth was on a trajectory to surpass 2º C above pre-industrial levels. ‘The amount of observed sea level rise in the Gulf is unprecedented and has sent scientists scrambling to determine the cause. The big question on everyone’s mind is whether the observed changes are temporary or a harbinger of much faster rise in ocean levels in the Gulf of Mexico.

Higher Than Expected Sea Level Rise

Higher sea levels are already having a negative impact on coastal areas that abut the Gulf of Mexico. One study suggests that recent devastating hurricanes, including Michael in 2018 and Ian last year, were made considerably worse by a faster rising ocean. Federal tide gauge data from the National Oceanic and Atmospheric Administration suggest that sea level, as measured by tide gauge at Lake Pontchartrain in New Orleans, is eight inches higher than it was in 2006, just after Hurricane Katrina. Stop and ponder for a moment what 8 extra inches of water would mean for New Orleans if a similar storm hit the city today?

“The entire Southeast coast and the Gulf Coast is feeling the impact of the sea level rise acceleration,” said Jianjun Yin, a climate scientist at the University of Arizona and the author of a study published recently the Journal of Climate. His research calculates the rate of sea level rise in the Gulf of Mexico since 2010 at more than one centimeter per year for a total of nearly 5 inches in total through 2022. That is more than double the global average rate of about 4.5 millimeters per year since 2010 based on satellite observations of sea levels from researchers at the University of Colorado at Boulder.

While the annual totals might sound minor, even small changes in sea levels over time can have destructive consequences. Yin’s study suggested that Hurricanes Michael and Ian, two of the strongest storms ever to hit the United States, were made considerably worse in part because of sea level rise. “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,” Yin said.

“Unprecedented” Sea Level Rise

A second study by a long list of sea level experts, led by Sönke Dangendorf of Tulane University and published in Nature Communications, finds the same trend since 2010 across the U.S. Gulf Coast and southeastern coastlines, calling the rise “unprecedented in at least 120 years.”  Dangendorf told the Washington Post, “It’s a window into the future.” The rates at which sea levels are rising along the Gulf of Mexico have been so high in recent years, Dangendorf said, they are similar to what would be expected at the end of the century in a very high greenhouse gas emissions scenario.

Two other studies on rapid sea level rise and how it is affecting the Gulf Coast have been released by scientists in preprint form but have not yet passed through peer review. Taken together, they are remarkable because they connect the rapid rise of sea levels to profound changes in the ocean. In parts of Texas and Louisiana, sinking land has also been a long term factor that contributes to sea levels rising relatively quickly over time. But in the latest studies, scientists show a rapid rise of sea levels in places such as Pensacola and Cedar Key, Fla., where the land is not sinking as rapidly as it is in places such as Grand Isle, Louisiana, or Galveston, Texas.

In general, higher sea levels in the Gulf of Mexico and around Florida mean that hurricane risks in some of the most exposed and storm-prone parts of the United States are growing more acute. In addition, people continue to move to high-risk areas along the coasts. The scientists say millions of acres of land and hundreds of thousands of homes and offices could slip below high tide lines. Experts from the nonprofit First Street Foundation also projected recently that properties in many coastal areas could lose value as flooding intensifies, a shift that could harm homeowners and erode local tax bases.

Scientists are not entirely on the same page about the causes driving the phenomenon, or whether the recent acceleration in rising seas will continue at such a rapid pace. Researchers typically prefer to rely on decades of data to be more certain of trends in the climate system, and their causes. In that context, the recent sea level rise has happened over a relatively short time period. That makes the trend as ambiguous as it is worrying

Warmer Water Expands

The rapidly rising sea levels observed by the researchers appears to start in the Gulf of Mexico, which has been warming far faster than the global ocean. Warm water expands, which contributes to rising sea levels. That warm water also gets carried by currents out of the Gulf and along the East Coast, affecting places such as Georgia and the Carolinas.

The waters that have helped drive up sea levels in Gulf of Mexico are very warm even at deep levels, based on a preprint study by Jacob Steinberg and colleagues at the Woods Hole Oceanographic Institution, NASA’s Jet Propulsion Laboratory, the University of Hawaii at Manoa, and the National Center for Atmospheric Research. Steinberg and his colleagues suggest the trend implicates a warm current called the Loop Current, which enters the Gulf from the Caribbean Sea and in turn is part of a broader pattern of circulation in the Atlantic Ocean.

Dangendorf disagrees. His study suggests the cause of rising water levels in the Gulf is a combination of factors, some of them natural. Based on sea level records from Pensacola and Galveston, which date back a century or longer, the Gulf Coast also saw a rapid rise in sea level in the 1940s, a trend that subsided by the 1950s. It is not yet clear if the current observed rise in sea levels may also be an aberration of relatively short duration.

“We have this forced acceleration, but then on top we have that natural variability, and over the last couple of years we were unlucky, having that acceleration superimposed on natural variability,” he said. Nevertheless, he called the rapid sea level changes troubling, as they are like what scientists once would have expected only if the world kept pumping massive amounts of planet-heating gases into the atmosphere.

Which of course is what the nations of the world have continued to do, despite the scientific research linking higher levels of carbon dioxide to higher global temperatures. Their excuse is that scientists don’t agree among themselves, and until they do, there is no reason to disrupt a perfectly good economic system. That makes sense to a lot of people.

Effects Of Sea Level Rise Magnified

The effects of rising ocean levels is magnified in low lying area with little elevation change — which is common along the Gulf Coast. In those communities, even small amounts of sea level rise can make storms much more dangerous. Waves push closer to shore, worsening erosion. Surges push farther inland and erode coastal wetlands rapidly.

A fourth study in preprint form, by scientists with the University of Miami, NOAA, NASA, and multiple institutions in the United States and Australia, finds that the major rise in sea level in the Southeast since 2010 accounts for “30-50% of flood days in 2015-2020.” It notes that “In low-lying coastal regions, an increase of even a few centimeters in the background sea level can break the regional flooding thresholds and lead to coastal inundation.”

A Blip Or A Trend?

The critical question is whether the current rates of change documented by researchers will continue, leading to well over a foot of additional sea level rise in coming decades, or if they will return to levels more in line with global averages. Based on sea level records from Pensacola and Galveston, which date back a century or longer, the Gulf Coast also saw a rapid rise in sea level in the 1940s, a trend that had subsided by the 1950s. But it is not yet clear if this event will prove similar. Overall, the pace of sea-level rise is accelerating globally, and scientists have been unequivocal that seas will continue to rise well into the future, even if humans manage to drastically cut greenhouse gas emissions.

In a report last year, NOAA and other federal agencies found US coastlines on average are expected to see an additional foot of sea level rise over the next three decades. The report gave particularly high projections for the Gulf Coast, in significant part because of recent trends. “It’s very difficult for me to say what’s going to happen in the near term,” said Ben Hamlington, a NASA sea-level expert and a co-author on Steinberg’s study. “It’s not like these rates are immediately going to turn around.”