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NEWPORT –– The ocean covers the place where once-popular Perrotti Park used to be. The park benches that stood on dry land are gone. So are the water fountain and coin-operated binoculars through which visitors once observed the harbor.

Adjacent to the park site, America’s Cup Avenue is history, too, along with the harbormaster’s building and the salon, restaurant and stores that did business on nearby Long Wharf.

It is 8:16 a.m. on Tuesday, Nov. 2, 2100.

The highest naturally occurring tide of the year has come in, further emphasizing a distressing reality: the City by the Sea is now a city increasingly under the sea. Since the year 2009, sea levels have risen at least 3 feet. Even during regular tides, the ocean reaches in to claim more and more of the shore. Every coastal community in Rhode Island, not just Newport, has been affected.

Buildings have been lost, roads displaced, parks submerged. Wells have gone bad, polluted by encroaching salt water. Septic systems have failed. Beaches and valuable coastal wetlands have disappeared. Even moderate storms now cause unprecedented damage as waves and surges at least 3 feet higher than nine decades before pack an unprecedented punch.

This is no science-fiction scenario.

This is the most optimistic real-life projection that scientists today make for the year 2100 –– a year in which some people born in 2009 will still walk the earth. A less optimistic scenario calls for the sea to rise 19 feet from today. If that happens, fish would swim where this article was written, in downtown Providence.

While the ordinary citizen today may not lose sleep over these visions of tomorrow, officials are paying attention.

“It’s reality,” says state Sen. V. Susan Sosnowski, who chairs the Senate Committee on Environment & Agriculture. “The sea is rising.”

“It’s on our radar screen,” says Paige Bronk, Newport’s Director of Planning, Zoning and Inspection, who accepts the 3-foot projection for the year 2100.

The challenge is preparing.

“We have a pretty good understanding of what’s being projected,” Bronk says. “In terms of how we’re going to adapt, at the moment we don’t have the answers.”

“We’re teetering as a society on a close edge,” says Grover J. Fugate, director of the state Coastal Resources Management Council. “One of the concerns, obviously, is whether the political systems can react quickly enough and start to deal with it.”

That the sea is rising is beyond dispute: recorded measurements from Newport show that the sea there has risen half a foot since 1929, the first year that precise measurements were recorded. And the cause is global warming, a phenomenon that only a few now dispute.

“Warming of the climate system is unequivocal, as is now evident from observations of increases in global average air and ocean temperatures, widespread melting of snow and ice and rising global average sea level,” the Intergovernmental Panel on Climate Change concluded in 2007. Run by the Geneva-based World Meteorological Organization and the United Nations Environment Programme (headquartered in Nairobi, Kenya), and informed by the work of hundreds of scientists, the IPCC is the planet’s pre-eminent climate assessment body.

In its chapter on North America, the IPCC stated with “very high confidence” that not only is sea level rising on this continent but the rate of rise is accelerating –– and the consequences for human life will be significant, given the large numbers of people who live on or near the coast. Population trends provide no comfort, with projections seeing more people living in coastal regions as the years unfold –– an additional 25 million people in the coastal United States alone by the year 2032.

“Population growth and the rising value of infrastructure in coastal areas increases vulnerability to climate variability and future climate change,” wrote the chapter’s authors, a group of 20 scientists from the United States, Canada and Great Britain.

“Current adaptation is uneven and readiness for increased exposure is low.”

If this were a mine, the canary would have stopped singing.

KATE MORAN, professor of oceanography and ocean engineering and associate dean of the University of Rhode Island’s Graduate School of Oceanography, sits in her office on the shore of Narragansett Bay. She is discussing the IPCC report.

“There was this footnote that not many people noticed,” she says. “And it said: ‘By the way, these projections do not include the dynamics of ice sheets.’ ”

In layman’s terms, ice in Greenland and Antarctica is melting –– but the IPCC has yet to assess the full impact of the resulting water that’s entering the oceans. Unlike measuring tides or temperatures, a straightforward process, scientists do not completely comprehend what’s happening at the poles. That complicates projections.

“It’s one of the top questions in science today,” Moran says.

This is unquestioned: as the atmosphere heats, the water beneath it warms. And when water warms, it expands. Expanding ocean water raises sea levels. Some of the rise measured at Newport (and at other points globally) since 1929 can be attributed to a simple law of physics.

Ice melting on a massive scale is a more complex phenomenon, one involving a vicious circle. As global temperatures rise and icebergs increasingly melt, they not only produce water –– their white, reflective surfaces disappear, and a natural protection against the sun’s energy is lost. The CRMC’s Fugate explains:

“Ice itself reflects about 90 percent of the sun’s radiation back into the atmosphere. Sea water absorbs about 90 percent of the sun’s energy. So as we start to lose more ice and expose more open ocean, we’re going to get a warming effect from that alone –– regardless of the greenhouse gases that we put into the atmosphere.”

In this hemisphere, the cycle affects the Arctic ice cap and the Greenland ice sheet, a gigantic reserve of frozen water covering nearly 700,000 square miles (more than three times the size of France) that in some spots is almost 2 miles deep. As temperatures rise, more of the Greenland (and Antarctic) ice sheet melts and slips into the ocean.

“Glaciologists don’t really understand this rapid expulsion of ice,” Moran says.

But they agree it is an unwelcome development –– and as it measurably accelerates, it pushes projections of sea-level rise higher. According to Moran, projections from just five years ago are now considered “dramatically” low.

“That’s why scientists are speaking out,” Moran says.

In an article published on March 15 in the journal Nature Geoscience, author Jianjun Yin of the Center for Ocean-Atmospheric Prediction Studies at Florida State University said that ocean levels do not rise at a uniform rate. His study of ocean currents led him to predict that New England and the mid-Atlantic will see the sea rise an additional eight inches in those areas compared to other parts of the world.

“It’s not just waterfront homes and wetlands that are at stake here,” Donald Boesch, president of the University of Maryland Center for Environmental Science, who did not participate in the study, told the Associated Press. “Those kinds of rises in sea level, when placed on top of the storm surges we see today, put in jeopardy lots of infrastructure, including the New York subway system.”

AT HIS COMPUTER in the Wakefield headquarters of the CRMC, Fugate opens a slide presentation on the impact of sea-level rise in Rhode Island in the year 2100. Images produced by URI’s Rhode Island Sea Grant program illustrate the change at eight locations around the state under the most optimistic projection: a rise of 3 feet.

For each location (including Newport’s Perrotti Park and Ida Lewis Yacht Club, Pawtucket’s State Pier, and Providence’s Waterplace Park), Sea Grant has produced three slides: a photo of a regular high tide today, a visualization of a regular high tide 91 years from now, and a visualization of a “spring tide” (an infrequent but naturally occurring tide) in the year 2100. Clicking through the slides, Fugate says:

“This is Ida Lewis. Gone. This is the state pier up in Pawtucket. Gone. This is Waterplace Park. Watch the walkways. That’s just 3 feet of sea-level rise. Now you can imagine if you take two meters … ”

The 3-foot (or about 1-meter) projection, Fugate says, is predicated on an improbable assumption: that carbon emissions, one of the causes of global warming, ended in 2009. While some governments are moving toward curbs on emissions, goals and dates of implementation are uncertain. It will be many years –– probably decades –– before the world moves beyond fossil fuels. The planet will continue to warm.

Which has prompted some to predict that sea levels will rise significantly higher than 3 feet. In a study released in 2006, several scientists led by Brown University graduate Jonathan T. Overpeck maintained that if current warming trends continue, enough ice will melt to raise the sea 6 meters –– almost 20 feet.

“This is a real eye-opener set of results,” Overpeck said when the study, financed by the National Science Foundation, was published in the March 24, 2006, issue of Science Magazine. Overpeck is director of the University of Arizona’s Department of Geosciences’ Environmental Studies Laboratory, a leading group.

Were all of the ice in Greenland and Antarctica to melt at some point in the distant future, scientists calculate that the oceans would rise by more than 200 feet. Much of Rhode Island and nearly all of Cape Cod would disappear.

EVEN AT 3 FEET, the result of sea-level rise would be manifest. A park no longer there is –– except for memories, no longer there.

Other effects may not be as widely apparent, but their impact will be greater. Salt infiltrating wells will leave them undrinkable. Water rising in leach fields will ruin septic systems. Vanishing coastal wetlands will leave some areas more susceptible to storm damage, as these wetlands’ ability to absorb water diminishes. Lo w places such as Florida and New Orleans know this already from deadly experience.

“Katrina was so severe, in part, because they have lost so much of their wetlands,” Fugate says. “There was nothing to abate the force.”

More subtle will be the diminished capacity of saltwater marshes to naturally process nitrogen, which feed algae blooms in Narragansett Bay (and other waters). Dying algae from these blooms settle to the bottom, where bacteria feeding on the dead matter deplete the water of oxygen.

“That, of course, is lethal to juvenile fish forms,” says Fugate.

In contemplating a future in which Rhode Island’s nickname, the Ocean State, will find unfortunate new meaning, planners are looking to the federal government and the CRMC for guidance in preparing for the inevitable.

“That is their charge –– to work on coastal planning,” says Senator Sosnowski, who represents South Kingstown and Block Island, coastal communities both.

According to Fugate, the CRMC is working with other state agencies to revise building codes for the latest projected levels and on other issues. The CRMC is also working with other states and the federal government, sharing information with local communities.

Fugate says the state and world must move to alternative energy sources as soon as possible.

“We’re going to have find ways of getting a hold of this carbon monster,” he says. “There is a sense of urgency. Some of the climate scientists are giving us essentially two decades before this train can’t be turned back. Unfortunately, we as society often wait for more visible signs. And by the time you get visible signs, a lot of times it’s too late.” More on the Web

•The Greenland Ice Sheet Project 2, which measured the depth of the Greenland ice sheet, is at http://www.gisp2.sr.unh.edu/GISP2/

•The Intergovernmental Panel on Climate Change’s 2007 report can be found at http://www.ipcc.ch/ipccreports/ar4-syr.htm

•NOAA measurements of mean sea level rise in Newport from 1929:

http://tidesandcurrents.noaa.gov/sltrends/sltrends_station.shtml?stnid=8452660

•“Paleoclimatic Evidence for Future Ice-Sheet Instability and Rapid Sea-Level Rise,” by Jonathan T. Overpeck and others, March 24, 2006, Science magazine, http://www.sciencemag.org/cgi/content/abstract/311/5768/1747

•A computer-generated map of Providence if the sea rises 6 meters is at http://www.uri.edu/hc/images/Lucht_poster.pdf

•A computer-generated map of southern New England if all of the ice melted at both poles is at: http://www.uri.edu/hc/images/Jordan_Poster.jpg

•Tides for every day through the year 2100 (minus 3 feet of sea level rise) are at http://tbone.biol.sc.edu/tide/tideshow.cgi

gwmiller@projo.com