A recent Rutgers-led study found that the rate of sea level rise along the U.S. Atlantic Coast in the 20th century was the fastest in approximately 2,000 years.
Jennifer S. Walker, the lead author of the study and a postdoctoral associate in the Department of Earth and Planetary Sciences, said that relative sea level rise is caused by local, regional and global-scale processes.
Local-scale processes include sediment compaction and human groundwater withdrawal, whereas regional-scale processes include changes in atmospheric and ocean circulation as well as land subsidence, which is the sudden sinking of the ground’s surface, she said. Global-scale processes include ice melt and warming oceans.
“The rate of sea level rise has gone up so drastically in the 20th century due to the increasing global contribution,” Walker said. “Climate change has accelerated ice melt and warming oceans, which in turn has increased the rates of sea level rise.”
For the study, the researchers used a “sea level budget” approach in which they examined the breakdown of the different processes that impact sea level change, Walker said. They did this by using long timescales at six sites along the Atlantic Coast.
“Different processes will each contribute a certain amount to sea level change, and added together, you have a total sea level rate from those controlling processes,” she said. “Producing a budget for six individual sites along the same coastline also allows us to compare the budgets among the sites.”
The researchers used five previously published sea level reconstructions from Connecticut, New York City, southern New Jersey and North Carolina, as well as produced a new sea level reconstruction in northern New Jersey, Walker said. They used a statistical model to break down the sea level records into global, regional and local components to produce the budgets.
She said the team wanted to examine long-term sea level change for both predictive and research purposes. In order to do this, they used a larger timescale compared to previous research, 2,000 years in comparison to individual centuries, and they produced sea level budgets at individual locations on the Atlantic Coast, whereas sea level budgets are typically done globally.
“Having a better understanding of sea level change in the past allows us to better predict how sea level will change into the future,” she said. “Additionally, with a longer-term understanding of sea level change over 2,000 years, we can see the variability of controlling processes through time, and it really puts in perspective the significant increase in rates of sea level rise in the last 100-200 years.”
While the larger timescale allowed for greater predictability of future sea level rise, the individual site-specific understanding of sea level change is important in regards to informing local projections of sea level change and improving coastal planning and preparedness, Walker said.
The significance of the study, she said, is that on long 2,000-year timescales, the regional component of the budgets is usually the dominant cause of relative sea level rise. Though, in the 20th century, the global component of the budgets became the dominant contributor due to ice melt and warming oceans.
“(Due to) the increase in the global component, rates of rise in the 20th century were more than double that of the average over the last 2,000 years,” Walker said. “So we've seen a shift in the budget components in the last few centuries as the global contribution is increasing which is caused by climate change.”
She said the next steps are to apply this sea level budget method using long-term sea level reconstructions to more sites globally.
With the availability of high-resolution data, the researchers can produce further sea level budgets, which will allow them to break down controlling processes in more detail and to compare across more locations, Walker said.
“Using this consistent method will help to give us a more global understanding of past sea level change at individual sites, including the recent acceleration in rates of rise,” she said.