Sea level rise is accelerating in Florida, scientists warn

DAYTONA BEACH, Fla. (AP) — Clay Henderson has lived on the same block along the Indian River in New Smyrna Beach for 34 years. Living in a storm-prone state like Florida, you expect to see a river top its bank on occasion, but only in the past two years has Henderson seen it happen on sunny days.

He hears similar stories almost everywhere he travels in Florida. In dozens of locations along the state's 1,350-mile coastline, sea level rise is no longer an esoteric discussion or a puzzle for future generations to solve. It's happening now and is forecast to worsen over the next 20 to 30 years.

Canal systems in Fort Lauderdale and Coral Gables have become a liability. For officials in Port Orange and Longboat Key, fortifying storm drains against encroaching seawater is a concern. Along the Withlacoochee River on Florida's Gulf Coast and the Matanzas River at Marineland, residents report finding saltwater species they've never seen before in those waterways.

Federal gauges stationed around the state's coast document the slowly rising water. After decades of almost imperceptible increases, the sea began rising faster about 30 years ago, said William Sweet, an oceanographer with the National Oceanic and Atmospheric Administration. It jumped again beginning in 2006. Now NOAA reports sea levels are rising along parts of the Florida coast by more than a third of an inch every year.

The average person visiting a favorite beach or fishing hole surely won't notice the difference. But soon, if the trend of the past 30 years continues, the impact will be hard to miss.

Henderson and others who have spent a lifetime on the water already notice a difference.

"Until the last couple of years, the only time the water would have come over the seawall would have been for a named tropical event or one of the extraordinary nor'easters," said Henderson, executive director of Stetson University's Institute of Water and Environmental Resilience. In the fall of 2015 and 2016, he said, "the water came out of the banks on cloudless, breezeless days."

A coast in peril

Mid-range projections by NOAA scientists — not the worst-case scenario — put the seas around Florida up to 17 inches higher by 2030, with the highest rise at Mayport, Fernandina Beach and Daytona Beach.

With just a 9-inch rise in sea level, NOAA advisories for coastal flooding capable of causing "significant risks to life and property" could occur 25 times more often, said Sweet, lead author of NOAA's January report describing the updated sea level scenarios. Higher seas would push seawater inland in waterfront areas along bayfronts in Sarasota and Apalachicola and in low-lying areas along the St. Johns, Suwanee and other rivers, flooding neighborhoods with increasing frequency and longer duration.

By 2070, the mid-range scenarios call for seas to be anywhere from 8 inches to 5.5 feet higher than today. By the turn of the century, NOAA projects the ocean could be as much as 10.5 feet higher, a height that could turn some of the state's most crowded communities into new scuba diving destinations.

Just three feet of sea level rise could force at least 1.2 million Floridians to abandon low-lying communities and migrate to higher ground, according to a study co-authored by Jason Evans, an assistant professor of environmental science at Stetson University. A six-foot rise could displace 6 million.

Scientists say the ocean began rising more than a century ago, averaging an almost imperceptible 1.5 millimeters a year from 1900 to 1990, based on data from a network of federal tide gauges around the country.

In the 1990s, the rising sea doubled its previous rate, reaching about an inch a decade, said Sweet. And then, over the past 10 years, tide gauges in Fernandina Beach, Mayport and Key West recorded an increase of about 0.9 centimeters per year, a little more than a third of an inch per year.

Whether that higher rate continues remains to be seen, said Sweet, lead author of a January report by NOAA, the South Florida Water Management District, the U.S. Geological Survey and others. The report, "Global and Regional Sea Level Rise Scenarios for the United States," uses information from tidal gauges around North America to show how sea level rise might occur regionally, based on local elevations and ocean depths.

The goal was to inform people, said Sweet, "so they can make smart decisions as they plan for the future."

Their research indicates that the sea will rise at least another 12 inches by 2100. NOAA's higher scenario projections indicate seas could rise as much as 11 feet in Bradenton and Daytona Beach and 10.75 feet in Panama City and Cedar Key.

Hard to soft butter

Seas have risen and fallen hundreds of feet in the ancient past. This time scientists at NASA, NOAA and other academic and governmental organizations say warming temperatures around the world — a result of increasing levels of greenhouse gases in the atmosphere — are to blame.

They report that warming, especially in the world's polar regions, is driving the melt occurring on land-based glaciers and ice sheets and the thermal expansion of warming ocean water. Federal studies show average sea surface temperatures have increased since 1980, in part because the ocean stores excess heat from the Earth's atmosphere, and as the water warms it expands, leading to additional sea level rise.

The two enormous ice sheets on Greenland and Antarctica are holdouts from the last ice age, said oceanographer John Englander, a Boca Raton resident and author of "High Tide on Main Street: Rising Sea Level and the Coming Coastal Crisis."

Greenland's ice sheet is 660,000 square miles and about two miles thick. Antarctica is 5.4 million square miles, covered by an ice sheet that averages a mile thick. Scientists with NASA, NOAA and other organizations say both ice sheets are losing gigatons of ice a year to melting.

At a lecture in Sarasota in April, University of Miami professor Harold Wanless described his visit to Greenland. It was a "sobering experience," Wanless said, to see ice sheets with rivers and lakes, fracturing "like going from hard butter to soft butter."

The melting of that land-based ice is akin to pouring water into a glass, said Englander. A land-based glacier moving into the ocean has a similar effect, like adding an ice cube to the glass of water.

While melting sea ice often attracts the splashiest headlines, it does not contribute directly to rising sea levels. But it is a crucial issue because federal scientists say thawing sea ice leads to additional warming. For example, with smaller areas of ice reflecting sunlight in the Arctic, open dark areas of water absorb the sun's energy instead and grow warmer. Scientists with NOAA and NASA say warmer temperatures as a result of declining Arctic sea ice are helping to thaw areas of permafrost and allowing additional greenhouse gases stored in the permafrost to escape into the atmosphere. That in turn leads to the warming that fuels sea level rise.

Scientists are working to understand just how much water the melting ice sheets could contribute to sea level, said Sweet. But the rate of ice sheet loss prompted Sweet and his colleagues to bump up their upper level estimates of sea level rise for 2100 and beyond.

Andrea Dutton, assistant professor of geology at the University of Florida, doesn't find the sudden increase in sea level rise surprising. Her study of the oxygen isotopes found in ancient coral reefs across the world shows the rate of sea level rise has always varied from decade to decade, she said. Her research will be used to help refine projections for how melting ice in Greenland and Antarctica could affect sea levels.

'Happening to us right now'

Regardless of what's happening in the world's polar regions, Bruce Mowry, city engineer for Miami Beach, is among those already dealing with the rising ocean. Sea level rise "is happening to us right now," Mowry said. "I'm out meeting residents every day talking to them about the impacts."

While the phrase rising seas prompts mental pictures of a rising ocean sweeping into beachfront hotels and homes — as it did in Daytona Beach during Hurricane Matthew last fall — the more pressing issues are the ones being encountered in Miami Beach and other neighborhoods that have drained their stormwater to the sea for generations.

The sea has begun pushing back, swelling with lunar high tides and storms, reversing the flow in drainage canals and flooding neighborhoods. Rising water infiltrates stormwater systems, coastal highways, septic tanks and fresh water wells.

Over the past couple of years in Miami Beach, "on a bright sunny day, the streets would fill with water," twice a day with the tide, Mowry said. The city's existing drainage system had created "avenues for water to come right into our city," he said. Now the city is spending $500 million to hold back the tide and prevent flooding. The city has installed check valves on storm drains, and is building up streets and sidewalks, as well as changing some of its building codes.

Stormwater is the No. 1 sea level-related issue already occurring, said Stetson's Evans, with most coastal communities in the Southeast United States already experiencing periodic stormwater drainage issues and failures.

The water level is 5 to 6 inches higher than when drainage pipes were installed 50 or more years ago, said Evans, who works with cities in Florida and Georgia on sea level rise issues. "When it rains heavily we have an issue because the water just can't get out of the canal or stormwater basin."

Most communities begin to plan because they are seeing saltwater in roads, said Evans, "and it's coming into their yards and killing their grass."

One of those communities is Longboat Key in Sarasota and Manatee counties, where residents have experienced "sunny day" street flooding in Longbeach Village, an older bayside neighborhood with the lowest elevation on the island.

Like other low-lying areas on bays and rivers, the island's shoreline on Sarasota Bay is more vulnerable than the dune-protected Gulf coast, Town Manager David Bullock said. During unusually high tides, seawater rises through the storm drains and enters the streets.

Lee Hayes Byron, Sarasota County's sustainability manager, watched that near the Mar Vista restaurant in Longbeach during one recent flooding event on a sunny day.

"When a boat went by," said Byron, "the puddle in the street moved."

Not every coastal local government has documented problems.

Walton County spokesman Louis Svehla said his northwest Florida community hasn't experienced any issues with sunny day flooding in their area.

A force multiplier

In South Florida, sea level rise is "a force multiplier," said Jim Murley, chief resiliency officer for Miami-Dade County. "It's slowly making natural events a little worse."

"Sea level rise is taking place so gradually you're not going to see it, but it's amplifying those events," Murley said. "People tend to overlook these events we need to be paying attention to."

Bob Whitener, a retired Marine, couldn't overlook the rising water at his family's cottage on Cedar Key. His family has vacationed in a cottage there for about 75 years.

In 2006, he spent $11,000 to raise the cottage four feet, to keep it safe from floodwater. Now other neighbors are doing the same thing.

"It seems like in the last decade, things have started heating up," Whitener said. In late May, he snapped photos in his backyard as seawater came up over the seawalls.

"High winds and a high tide from the southwest were blowing the water onto the island," Whitener said. "That's unusual."

Such issues are only going to get worse, said Thomas Ruppert, an attorney and coastal planning specialist with the Florida Sea Grant College Program. "If it seems like a big deal during a high tide now, you can bet your bottom dollar you'd better start thinking about it really quick."

Business is booming in backflow preventers as local governments and utilities try to keep the ocean from infiltrating stormwater systems. One of those cities is Fort Lauderdale, which has billed itself as "America's Venice" since the 1920s.

"Turns out that was pretty darned appropriate," said Ruppert. "It has a little ironic ring to it now."

Venice, Italy is working to complete a set of $6 billion floodgates to hold back rising seas. Meanwhile, to keep Fort Lauderdale's canal-laced neighborhoods from flooding, Ruppert said the city is installing backflow preventers and upgrading drainage systems.

In St. Augustine, the nation's oldest city, nuisance flooding is now happening more than a dozen times a year, said Mayor Nancy Shaver.

Kathryn Frank, an assistant professor in the department of urban and regional planning at the University of Florida, has worked to document sea level rise on both coasts, in Flagler, St. Johns and Levy counties. In Levy County, Frank said, old-timers have described islands that are disappearing and places they can reach in their boats that they couldn't before.

But defining the potential impacts of rising seas along Florida's coast is not easy because so many changing dynamics are at work all at once. For example, Evans and Frank said it's difficult to tease apart the factors driving erosion and other changes along the beach.

Erosion can't be blamed on a single factor, said Evans. "But as the ocean rises, it will make that issue worse." Florida already spends millions of dollars to battle beach erosion every year, and studies differ on whether beach renourishment helps or worsens erosion.

But the powerful storm surges from Hurricane Matthew and Hurricane Hermine in 2016 seemed to offer a glimpse of the damage that could occur in the future. Saltwater poured into seaside communities from Sarasota north to Apalachicola on the Gulf Coast and from New Smyrna Beach to the Carolinas on the Atlantic Coast. In many cases, the water remained for days.

Scientists haven't determined whether higher seas worsened the widespread flooding, but they say the flooding illustrates the state's vulnerability to the sea. If sea levels continue to rise, for example, higher seas would lead to more devastating impacts from storm surge.

In Flagler County, Hurricane Matthew's erosion damage could cost more than $50 million to repair.

In Cedar Key, Hurricane Hermine's storm surge measured 7.5 feet. Topped by powerful waves, it pushed water levels to a record 6.1 feet above the mean higher-tide mark. Records on the island date back to 1914. Kathryn Frank, the UF researcher, said one road in the town remained flooded for a week. So did a spot on the main highway to the island archipelago. Other low-lying areas in Cedar Key remained flooded for a month.

"Those are the places that are just going to get worse," she said. "They're vulnerable because they're low-lying and sea level rise will make that much more difficult."

The sea's insidious reach

Hermine created another issue that's forecast to occur with increasing frequency.

The water table, the shallow layer of groundwater under most of Florida, will get higher, said Sweet, the NOAA oceanographer. Ocean water interacts with underground aquifers and the higher density saltwater displaces the fresh water.

It also will take fewer inches of rain for the soil to become saturated, said Frank. "It will flood more easily and the floods will stay longer because the water table is higher."

Florida's geographic location adds two additional factors that could contribute to higher-than-average sea level rise: its proximity to the Gulf Stream and the influence of the earth's gravitational forces.

The Gulf Stream, a seawater current that parallels the Florida Coast in the Atlantic Ocean, is seasonal and typically slows down in the fall, Sweet said. It's also sensitive to changes in atmospheric pressure, winds and disturbances along a region influenced by the Bermuda High, a ridge of high pressure that expands and shrinks across Florida and the western Atlantic Ocean.

"When the Gulf Stream slows down, coastal sea levels rise," said Sweet. Since the mid-2000s, "there's a noticeable, more prolonged slowdown."

Gravity could come into play as the melt continues on Antarctica and Greenland, said Sweet. For now, the "tremendous ice" pulls water closer, he said. As it melts and the seas rise, the gravitational pull will be less and the water will be released to go elsewhere. Some forecasts, he said, call for it to pool higher around Florida, which will be "particularly sensitive to the reduction of ice in Antarctica."

Long before flooding permanently swamps low-lying parts of Florida, Sweet said people who live along tidally influenced bodies of water, such as coastal rivers and tidal creeks, will begin experiencing rapid increases in the frequency and duration of tidal flooding. Using the mid-range scenarios, NOAA projects that could be happening by 2030-2040.

The change won't be gradual, said Sweet. "It's going to be happening by leaps and bounds."

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