Protecting U.S. coastlines from rising sea levels could cost an estimated $400 billion over the next 20 years, according to a study published Thursday.

The report by Resilient Analytics and the Center for Climate Integrity estimates that more than 50,000 miles of coastal barriers, or sea walls to mitigate rising ocean levels, will need to be constructed in 22 states.

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More than 130 counties face at least $1 billion in costs, according to the report, and 14 states will see expenses of $10 billion or greater between now and 2040.

"These costs reflect the bare minimum coastal defenses that communities need to build to hold back rising seas and prevent chronic flooding and inundation over the next 20 years," researchers wrote in the report.

"They represent a small portion, perhaps 10 to 15 percent, of the total adaptation costs these local and state governments will be forced to finance during that time and into the future."

The researchers noted that the costs for some small communities and counties will be too large for them to cover individually.

According to the Intergovernmental Panel on Climate Change, global sea level rise is expected to increase by 11 to 24 inches by 2100 under a scenario in which the world limits global warming to 2 degrees Celsius above pre-industrial levels. Thursday's report calls such a scenario “modest.”

Under scenarios deemed "more plausible" by researchers, sea levels could rise almost 40 inches by the end of the century if the world fails to reign in emissions more stringently.

“We purposefully analyzed more moderate and immediate scenarios to direct the policy discussion toward decisions that need to be made right now,” the report states. "This conservative approach is by design, and is intended to shine a light on near-term costs and choices that cannot be avoided."