“Unprecedented” sea level rise observed along U.S. coasts
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Sea level rise has long been expected to be an ongoing and worsening problem for U.S. coasts, but scientists have found that some areas are experiencing “unprecedented” levels of rising seas, raising concerns about the fate of already vulnerable communities.
A new study published in Nature Communications on Monday found that since 2010, sea level rise along the nation’s Southeast and Gulf coasts has ramped up dramatically, hitting rates that are “unprecedented in at least 120 years.” Since 2010, scientists from Tulane University have found that sea levels in those regions have increased by about half an inch every year.
“These rapid rates are unprecedented over at least the 20th century and they have been three times higher than the global average over the same period,” said Tulane professor Sönke Dangendorf, who led the study.
Numerous factors play a role in this sea level rise, scientists found, including those that are both natural and human-made. Study co-author Noah Hendricks said that they looked at those causes, including vertical land motion, ice-mass loss and air pressure, but that “none of them could sufficiently explain” the rampant rise.
“Instead, we found that the acceleration is a widespread signal that extends from the coasts of the Gulf of Mexico up to Cape Hatteras in North Carolina and into the North Atlantic Ocean and Caribbean Seas,” he said in a statement, “which is indicative for changes in the ocean’s density and circulation.”
The area in question – located in the Atlantic Ocean – is known as the Subtropical Gyre. Scientists said that this region has been expanding during the same timeframe the study took place. Changing wind patterns played a role in that expansion, but another significant factor is the warming of the ocean waters – as ocean temperatures increase, the ocean expands and takes up more space, leading to an increase in sea levels.
The ocean absorbs 90% of warming on the planet, meaning that as humans continue to conduct activities that contribute to that – namely the burning of fossil fuels – the more the oceans will warm and the more that sea ice will melt, adding to sea level rise.
In November, NASA found that sea levels along U.S. coastlines could increase by as much as a foot by 2050. Like the Tulane study, NASA found that the Southeast and Gulf coasts will face “substantially higher” rates of rise.
Another recent study produced similar findings to those at Tulane. In that study, published in the American Meteorological Society’s Journal of Climate in March, scientists found a “rapid decadal acceleration of [sea level rise]” from 2010 to 2022 along areas of the East Coast and Gulf of Mexico. The Southeast and Gulf coasts had the “most notable” increases, the study found, with rates of about 0.4 inches a year during that period.
“While [sea level rise] was thought as a slow and gradual process, our results show that ocean dynamics can change regional sea level rapidly,” lead researcher Jianjun Yin said, “leaving less time for the coastal communities to mitigate and adapt.”
This faster rate of sea level increase means that these areas have been made more susceptible to flooding and storm damage, and could see “accelerating land loss in the most vulnerable settings,” scientists said. And if that rate should increase, scientists said in their paper, it could “threaten the national security of the U.S.”
The scientists from Tulane did say, however, that the increase seen in the last decade may not be a permanent fixture and could be the result of yearslong weather events combined with “man-made climate change signals.” But that’s “no reason to give the all clear,” study co-author Torbjörn Törnqvist said.
“These high rates of sea-level rise have put even more stress on these vulnerable coastlines, particularly in Louisiana and Texas where the land is also sinking rapidly,” Törnqvist said.
Researchers in Texas found last year that there are “significant rates” of the ground sinking in the Houston metro area. The issue, known as subsidence, used to be “rare,” researcher Shuhab Khan said, but now, “it’s all over the world.”
“There are 200 locations in 34 countries where there’s known subsidence,” the University of Houston professor said. “Cities in the northern Gulf of Mexico, such as Houston, have experienced one of the fastest rates of subsidence.”
With all of this under consideration, Tulane’s Dangendorf said that measures to combat sea level rise and its impacts on coastlines cannot stop, even if the recent spike was only temporary.
“The results, once again, demonstrate the urgency of the climate crisis for the Gulf region,” Dangendorf said. “We need interdisciplinary and collaborative efforts to sustainably face these challenges.”