Communities across the U.S. are underestimating future sea level rise, according to a study published in Earth’s Future, a journal from the American Geophysical Union. The study found that more than half of the 54 surveyed locations in the U.S. underestimate the upper end of future sea level rise, compared to regional projections from the Intergovernmental Panel on Climate Change (IPCC).

“Our goal was to understand how well scientific advances in understanding sea-level rise are being incorporated into the local assessment reports,” said lead author Andra Garner, assistant professor at Rowan University in New Jersey. ​The answer in the report? Not very well.  

“Everyone has the same kind of information, such as IPCC reports. But the information tends to be used in very different ways, resulting in different levels of preparation for future sea level rise,” she said.

The team collected local assessment reports for the U.S. and analyzed the most recent report for each location. They then created a database that includes information about each community’s assessment, including sea-level rise projections, future emission scenarios, and the lower, central, and upper sea-level rise estimates. They compared these projections to the actual sea level rise.

The reports and projections in the new study are grouped by region, and they revealed some differences. The Northeast and West both have many locations that include projections beyond 2100, but there are no such long-term projections for the South. Many projections for the South included only broad estimates.

Communities discussed in the report that underestimate future sea level rise, included the lower Mississippi, such as New Orleans.

According to John Englander, an oceanographer and head of the Rising Seas Institute, even the IPCC, the benchmark for many estimates, is lowballing sea level rise.

“The IPCC is very light on contributions like Antarctic melting, which is proceeding faster and faster,” he said. “Based on just the geologic record, it’s safe to say it’s going to surprise us. Our tendency is to understate.”

“It’s a little like predicting the next earthquake in San Francisco,” said Englander. “We can’t predict those things. We have statistical probabilities, but the collapse of the Greenland ice sheet just can’t be predicted.”

The implications of the new study are profound. Sea level rise projections around the world range from serious to catastrophic. Norfolk, Virginia, is home to the world’s largest naval base, Naval Station Norfolk, which employs thousands and supports 75 ships. Sea level is expected to rise between one and three feet by 2050. Flooding today can prevent children from taking school buses. 

To avoid catastrophe, former base commander Joe Bouchard said, the base needs a complete overhaul. “The list is endless,” he said. “The electrical systems, telecommunications, everything is vulnerable.” The cost for adaptation will run into the billions, he said. (Norfolk is among the communities examined in the new study.)

Other parts of the world are in a situation even more dire. In the distant Solomon Islands, coastal erosion in the Pacific Ocean nation has been severe, stripping away at coconut plantations and even graveyards, according to Melchior Mataki, the country’s environment minister.

“Relocation is often perceived as a last option,” Mataki said. “Yet for some parts of our country, it is the only reasonable and sustainable option.”

The Netherlands has been keeping the sea at bay for generations with dikes, but increasingly the sea is winning. Once a thriving farming area, Noordwaard is now marshlands, designed to flood to keep nearby Dutch cities dry. 

“Several years ago, when you came to that polder, big nice farms were there, acres with potatoes and onions,” said Stan Fleerakkers, a dairy farmer who lives nearby. “Now when you drive there, there’s nothing left of it.”

Unfortunately, because carbon dioxide is fairly stable in the atmosphere, the situation can only get worse without major action, as carbon continues to accumulate. The carbon we emit today will remain in the atmosphere for hundreds of years.

United Nations Secretary-General António Guterres recently warned that rising sea levels due to climate change could spark a “mass exodus of entire populations” and increase the potential for conflict.

“The impact of rising seas is already creating new sources of instability and conflict,” he said at a U.N. Security Council discussion. “We would witness a mass exodus of entire populations on a Biblical scale.”

Avoiding to consider the worst case scenarios “…constricts the picture of what you are looking at,” said Garner. That could leave local governments more vulnerable to the less likely yet still very plausible upper bounds on sea level rise, said Garner. She and her colleagues are planning further research into how and why communities are underestimating sea level rise.

“There’s still a lot to explore here,” said Garner.