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Rising seas could swallow millions of U.S. acres within decades

New research finds an estimated 25,000 properties in Louisiana could slip below tidal boundary lines by 2050. Florida, Texas and North Carolina also face profound economic risks.

A beachfront home collapses along Ocean Drive in Rodanthe, N.C., on Feb. 9. (AP)

The water is coming.

There’s no longer much doubt about that, as scientists have increasingly documented how the warming of the planet has accelerated sea level rise along coasts around the world.

But an analysis published Thursday by the research nonprofit Climate Central reveals a troubling dimension of the economic toll that could unfold in the United States, as hundreds of thousands of homes, offices and other privately owned properties slip below swelling tide lines over the next few decades.

Here are five takeaways from the research about the people and places that stand to lose most, the likely ripple effects and reasons the world must cut its emissions of greenhouse gases in order to eventually stem the rising waters:

1. Sea level rise will shift coastlines — and property lines

Researchers at Climate Central took scientific data on projected sea level rise, as well as information about state tidal boundaries, and combined that with records on more than 50 million individual properties across hundreds of U.S. counties to identify parcels most likely at risk.

Their conclusion: Nearly 650,000 individual, privately owned parcels, across as many as 4.4 million acres of land, are projected to fall below changing tidal boundaries by 2050. The land affected could swell to 9.1 million acres by 2100. According to Thursday’s analysis, properties with a collective assessed value of $108 billion could be affected by the end of the century, based on current emissions. But, the authors noted, because complete property values were not available for all counties, the actual total is likely to be far higher.

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The changes also could come gradually at first, then quickly. In many communities, the authors wrote, structures are clustered in areas that historically are on safe ground. But once rising seas reach those densely developed elevations, “the number of affected buildings sharply increases.”

“As the sea is rising, tide lines are moving up elevation, upslope and inland,” said Don Bain, a senior adviser at Climate Central and an expert in sea level rise, who led the analysis. “People really haven’t internalized that yet — that ‘Hey, I’m going to have something taken away from me by the sea.’ ”

2. The Gulf Coast and Atlantic Coast stand to lose most

It’s no surprise that Louisiana, where the seas are swelling and land is sinking, faces a daunting loss of property in the years to come.

The Climate Central analysis estimated that more than 25,000 properties, totaling nearly 2.5 million acres in the state, could fall wholly below tidal boundary lines by 2050 — a number that far exceeds any other place in the nation. That would amount to 8.7 percent of Louisiana’s total land area, the report found.

But other states also appear to face widespread threats. The top three at risk behind Louisiana are Florida, North Carolina and Texas, all of which have large swaths of low-lying, imperiled coastlines.

While property across the Southeast might face the most collective risk, other states also have reason for concern. New Jersey and New York, for instance, also stand to see thousands of properties fall below tidelines in coming decades. Same for Maryland, which the researchers project could see more than 2,500 buildings impacted.

The impacts of sea level rise already are evident, as some communities face the prospect of retreat and a growing number grapple with nuisance or “sunny day” flooding.

Eventually, such issues will “transition from something that’s rare to becoming something that’s normal,” said William Sweet, an oceanographer and sea level rise expert at the National Oceanic and Atmospheric Administration’s National Ocean Service.

3. It’s not just about flooded homes. It’s about eroding tax bases.

The loss of homes and other properties — especially those along the waterfront — isn’t just a tragedy for owners. It is a surefire way to erode the revenue municipal governments need to operate.

“Ultimately, this is a local problem and a local story,” Bain said. “We finance local government through our property taxes.”

If sea levels continue to rise unabated, that poses more than just a problem to beaches and condos that line the coasts. It eventually will translate into fewer taxable properties, and less money to fund schools and fire departments, fix roads, maintain sewers and provide other essential services.

“Diminished property values and a smaller tax base can lead to lower tax revenues and reduced public services — a potential downward spiral of disinvestment and population decline, reduced tax base and public services, and so on,” Thursday’s analysis found.

4. The potential ripple effects are vast

Eroding tax bases are a big problem. But hardly the only one. The study also found a litany of other complications that likely will result as sea levels inch higher and higher.

“The legal and political ramifications of these changes are complex, and will likely vary among locations,” the analysis found. “Those ramifications extend well beyond loss of tax revenue as property owners object to paying taxes on submerged land.”

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Beyond those initial shocks, municipalities and individuals will also be forced to confront the significant costs for removing inundated structures and flooded septic tanks. Governments could be on the hook for properties that get abandoned, adding additional expenses not covered by their budgets.

But even before then, communities already are wrestling with the need to repair streets and roads damaged by flooding, as well as overwhelmed or outdated sewer and water systems. “How city and county management teams respond to these risks, or if they respond at all, is material to the city’s and county’s future ability to repay debt and protect its credit rating,” the authors wrote.

5. The future is not (entirely) set in stone

The world’s foremost scientists have found that given the carbon built up in the atmosphere after generations of burning fossil fuels, the rate of sea level rise is increasing and will continue over the next several decades.

Those findings are in line with a major report earlier this year from the NOAA, which found that sea levels could rise along U.S. coastlines by roughly a foot between now and 2050 — roughly as much change over the next three decades as over the past century.

“That trajectory appears somewhat set,” said Sweet, who was not involved in Thursday’s study.

What remains undetermined is how communities across the United States prepare for the changes they know are coming, and what this country and others do to slow the heating of the planet.

“If we get our act together, we can get to a lower curve, and that buys us time,” Bain said. “We don’t want [seas] rising so fast that it outpaces our capacity to adapt.”

Sweet said having access to reliable data hopefully gives public officials and individuals information they need “so they can make the smart choices to best defend and prepare against rising seas” — from shoring up infrastructure to making thoughtful decisions about development.

But ultimately, he said, the world must act in concert to make sure the problem doesn’t grow worse indefinitely.

“Emissions matter, especially as we get beyond the next 20 or 30 years,” Sweet said. “You reduce emissions, you reduce your likelihood of higher sea levels.”

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