To get a sense of how much it will cost the nation to save itself from rising seas over the next 50 years, consider Norfolk, Virginia.

In November, the Army Corps released a proposal for protecting the city from coastal flooding that would cost $1.8 billion. Some experts consider the estimate low. And it doesn't include the Navy's largest base, which lies within city limits and likely needs at least another $1 billion in construction.

Then consider the costs to protect Boston, New York, Baltimore, Miami, Tampa, New Orleans, Houston and the more than 3,000 miles of coastline in between.

Rising seas driven by climate change are flooding the nation's coasts now. The problem will get worse over the next 50 years, but the United States has barely begun to consider what's needed and hasn't grappled with the costs or who will pay. Many decisions are left to state and local governments, particularly now that the federal government under President Donald Trump has halted action to mitigate climate change and reversed nascent federal efforts to adapt to its effects.

Globally, seas have risen about 7 to 8 inches on average since 1900, with about 3 inches of that coming since 1993. They're very likely to rise at least 0.5-1.2 feet by 2050 and 1-4.3 feet by 2100, and a rise of more than 8 feet by century's end is possible, according to a U.S. climate science report released this year. Because of currents and geology, relative sea level rise is likely to be higher than average in the U.S. Northeast and western Gulf Coast.

By the time the waters rise 14 inches, what's now a once-in-five-years coastal flood will come five times a year, a recent government study determined. By 2060, the number of coastal communities facing chronic flooding from rising seas could double to about 180, even if we rapidly cut emissions, according to a study by the Union of Concerned Scientists. If we don't slash emissions, that number could be 360.

The costs from this inundation will be tremendous. One study, published in the journal Science in June, found that rising seas and more powerful tropical storms will cost the nation an additional 0.5 percent of GDP annually by 2100. Another, by the real estate firm Zillow, estimated that a rise of 6 feet by 2100 would inundate nearly 1.9 million homes worth a combined $882 billion.

Estimating what it would cost to avoid some of this is trickier. It will certainly be expensive—look no further than Norfolk's $1.8 billion—but some research indicates it may be less costly than failing to act. An analysis by NRDC found that buying out low- and middle-income owners of single-family homes that repeatedly flood could save the National Flood Insurance Program between $20 billion and $80 billion by 2100.

The Trump administration, however, has revoked or withdrawn at least six federal programs or orders intended to help make the nation's infrastructure more resilient to rising seas and climate change. That includes an executive order signed by President Barack Obama in 2015 that expanded the federal floodplain to account for climate change projections and limited or controlled any federal infrastructure spending within that zone. Trump revoked the order in August. Trump also disbanded a panel that was trying to help cities adapt to climate change.

"By and large, at every level of government, the nation is failing to recognize the challenge of sea level rise, much less address it in a proactive way," said Robert Moore, a senior policy analyst at the Natural Resources Defense Council.

Build Smarter, Move Away from the Risk

Moore said the country faces two main tasks: First, we have to stop building in risky, flood prone areas on the coast. Then we need to find ways to move people who already live there. One 2010 study estimated that 8.4 million Americans live in high-risk coastal flood areas.

Currently, federal policies including the National Flood Insurance Program are designed to encourage people to rebuild where they are, even if their properties are likely to flood again.

"What we do now is we basically wait for a disaster to happen and a massive disruption to occur and then we scramble around to get people back to where they were," Moore said.



Moore and others are pushing for reforms that would encourage buy-outs of willing homeowners. (The House passed a bill in November that would adopt some of these reforms.)

Creating the Next New Orleans

Beyond that, most current adaptation plans rely on walling out the water, raising roads or other infrastructure and pumping out flood waters, a process Moore likens to creating "another New Orleans."

R.J. Lehmann, editor in chief of the conservative think tank R Street, said we'll have to pick our battles by focusing on what's worth protecting. "You look to a city like Atlantic City, which is on a barrier island and is highly vulnerable to floods" and which by some accounts is a failed city economically, he said. "Will we go to extraordinary lengths to save a city like Atlantic City? I think the answer is no."

"We're not in the habit of making those bloodless decisions on the cost and benefit of saving infrastructure," he said. "We're going to have to."