A new study led by Rutgers University that looked at sea level rise at six locations on the East Coast over the last 2,000 years found that levels rose twice as fast in the 20th century compared with previous eras, and that South Jersey experienced the highest rates overall.
The authors concluded in the study published in the journal Nature Communications that global sea rise from melting ice and warming oceans from 1900 to 2000 increased at a rate more than double the average for the previous 1,800 years.
Sea levels don’t rise uniformly like water running into a bathtub, but rather are influenced regionally by both local and global factors. The authors took into account a complex array of influences including a natural sinking of the land due to geological reasons, ocean dynamics, and groundwater withdrawal.
The study looked at three locations in New Jersey: Leeds Point in Atlantic County, Cape May Court House in Cape May County, and Cheesequake State Park in Middlesex County. They also looked at East River Marsh in Connecticut, Pelham Bay in the Bronx, and Roanoke Island in North Carolina.
“We looked at the breakdown of processes contributing to sea-level rise at individual sites over the last 2,000 years to look at the influence of each contribution and how the contributions change over time,” lead author Jennifer Walker, a postdoctoral associate at Rutgers’ Department of Earth and Planetary Sciences in New Brunswick, said in an email.
She found that the sinking of land due to a retreat of the massive Laurentide ice sheet thousands of years ago, played the biggest factor in sea level rise for all locations over the 2,000-year span. The ice sheet, which covered all of Canada and most of the northern part of the U.S., placed megatons of pressure that bore down on the earth for thousands of years causing land to bulge in certain areas such as the East Coast. When it retreated, the bulges began to collapse, causing the land to slowly sink. The sinking will continue for thousands of years into the future.
But, in the 20th century, melting ice sheets and warming oceans became the dominant drivers of sea level rise, according to the study. The paper does not examine the source of warming oceans, though scientists agree greenhouse gas emissions by humans are the central cause.
Walker, who is from Media, Pa., has previously studied the impact of rising sea levels on New Jersey’s Atlantic white cedars, which are dying off in certain areas because of saltwater intrusion, causing so-called “ghost forests” in swampy areas near the coast.
Because there are no written historical records for much of the 2,000 years, Walker and her team used a statistical model for the new research that combined modern-era tide gauge data with sea level reconstructions over much longer timescales. They used records from salt marshes to reconstruct sea levels in North Jersey, and previously published reconstructions for other coastal areas.
The biggest surprise, Walker said, is how much ice melt and warming oceans were factors in the past 100 to 200 years.
“We knew sea-level has been rising in these locations over long timescales,” she said, “but now due to the global changes, those processes are becoming the dominant contributor to sea-level rise in the 20th century, resulting in rates that are double the long-term average over 2,000 years.”
She noted the researchers focused on the U.S. East Coast because it had the most records, but the methods can be applied elsewhere.
Walker said the two South Jersey locations, Leeds Point and Cape May Courthouse, saw the fastest rates over the 2,000-year span, with an average of about 1.6 millimeters of sea rise per year. However, she said that pace accelerated in the 20th century to about 3.6 millimeters per year, because of global sea level rise.
South Jersey saw the highest overall rates because of the outsized impact of sinking land due to the ice sheet retreat. So, while it is sinking more than other areas in the study, it is simultaneously experiencing a rising Atlantic Ocean.
Walker’s study analyzed data through the year 2000, but she said the rate has likely accelerated since then. Separate from the article, she cited data from tide gauge records in Cape May that show from 1965 to 2020 the rate of sea level rise was about 4.8 millimeters a year, or about 1.9 inches per decade.
She said that rates are expected to continue to rise. Though her study did not make projections, Walker said her findings bear out previous estimates by the Rutgers Climate Resource Center that New Jersey could experience a rise of slightly less than a foot to 2.1 feet between 2000 and 2050, and 6.3 feet by 2100 depending on the level of carbon emissions.
Her coauthors included scientists from Rutgers, Nanyang Technological University in Singapore, Maynooth University in Ireland, the University of Hong Kong, Bryn Mawr College, East Carolina University, and Durham and Liverpool Hope Universities in England.