New Orleans after Hurricane Katrina. Mark Moran, U.S. National Oceanic and Atmospheric Administration

The world’s coastal cities are some of the most beautiful, culturally vibrant and heavily populated urban areas. They are also some of the most popular places for summer vacations. However, rising sea levels threaten these areas.

The Earth's oceans rose by an average 7.7 inches (195 mm) between 1870 and 2004, according to a study in Geophysical Research Letters. Projections by the U.S. National Research Council warn that the seas could rise a further 22 to 79 inches (56 to 200 cm) during the 21st century.

Here are nine popular areas endangered by the encroaching ocean.

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New Orleans faces a double threat from both land and sea.

The muddy foundation of the city is not firm enough to support the city. As New Orleans sinks into its feet of clay, the Gulf of Mexico is rising around it.

The disastrous flooding after Hurricane Katrina in 2005 put the Big Easy on defense mode, but even the best efforts may not be enough.

Much of New Orleans already lies 5 to 10 feet (1.5 to 3 meters) below sea level. A report from the U.S. Geological Survey warned that the ocean could rise 8 to 13 feet (2.5 to 4 meters) above the city by 2100.

Rockaway New York , Nov. 11, graffiti signed with the message Global Warming on Rockaway beach in front of a home destroyed by Hurricane Sandy. Julie Dermansky/Corbis

New York City also experienced havoc wrought by the surging seas during a storm. After Superstorm Sandy submerged parts of the city and took the lives of 43 people, Mayor Michael Bloomberg called for a $19.5 billion project to build defenses and overhaul zoning regulations to stave off the effects of a rising ocean. That sum of money is roughly equal to the cost of Superstorm Sandy’s damage to the city.

Investing in preventive measures may save the Big Apple from future damage. Long Island and the lower Hudson River valley that underlies the city may experience ocean level increases of 12 to 23 inches (30 to 60 cm) by 2080, according to the New York Department of Conservation.

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Key West resident Gregorio Nodal walks in the flooded North Roosevelt Coast Boulevard after Hurricane Wilma hits Florida's southern west coast Oct. 24, 2005.CARLOS BARRIA/Corbis

Miami’s thriving beach culture, along with much of the rest of the city, may be swallowed by the Atlantic within the next century.

Unlike New York, levees and sea walls may not be effective in Miami. The porous limestone bedrock that lies beneath Miami could allow rising ocean levels to seep beneath the city. Underground fresh water supplies, or aquifers, in the area already suffer from contamination with salt water.

The National Oceanic and Atmospheric Administration created a sea rise simulation that allows users to map how much of Miami may be submerged.

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"The Entrance to the Grand Canal, Venice," circa 1730. Giovanni Canal/Museum of Fine Arts, Houston

The picturesque and romantic canals and bridges of Venice provide an architectural maze that connects hundreds of islands within Italy's Venetian Lagoon. But the city of islands has had a long history of flooding from the Adriatic Sea, and with sea level rise and subsidence knocking from both sides of the $6.7 billion flood gates under construction, the stakes are high to protect the city when the floating gates begin operation next year.

Comparisons of the modern city with paintings by Giovanni Canal from the 18th-century (shown above) suggest the city has sunk by more than 2 feet (60 centimeters) since 1727, reported the AP.

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The ongoing sinking of Venice combines with rising sea levels to increase the inundation of Venice by approximately .16 inches (4 mm) per year. By 2032, the city could sink another 3.2 inches (80 mm), reported Discovery News.

Floods inundate Bangkok.Daniel Julie, Wikimedia Commons

Bangkok attracts more than 10 million tourists per year, according to Thailand's Department of Tourism. However the threat of disastrous floods could dampen tourist's enthusiasm. For decades, Bangkok's use of groundwater sank the city into the very ground it was built on, but recent actions to curtail groundwater use have reduced the rate of the city's subsidence.

Still, the city of Bangkok suffered catastrophic floods in 2011 (shown above), and those inundations may have been a taste of the new normal for Thailand's capital. Bangkok and other coastal tropical cities may face higher sea level increases than northern cities, such as New York, plus an increasing number of tropical cyclones and hurricanes. Although many tropical nations, including Thailand, have contributed proportionately less to the causes of climate change than northern nations, tropical areas stand to suffer some of the worse damages from both rising oceans and temperatures.

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The laws of physics aren't doing anything to right this injustice. As ice from the poles melts, the water flows towards the equator and forms a bulge there due to the forces created by the Earth's rotation, according to a study published in Geophysical Research Letters. This causes the sea level to rise more in the tropics than in the north.

A cyclist braves floods on a road in heavy rain caused by Typhoon Haikui in Shanghai, China, on Aug. 8, 2012.Corbis

Shanghai's location at the mouth of the Yangtze River has made it a trading and travel powerhouse for centuries, but that location also makes it highly susceptible to flooding.

Research published in Natural Hazards found that Shanghai faces serious danger from the increasing ocean level and other climate change effects. However, city officials contend that the billions of yuan spent on flood control measures and storm water drainage have made the city more resistant to sea level rise, reported China Daily.

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A small boat passes a line of flood gates in Zeeland, Holland.Patrick Ward/Corbis

Beyond single cities, rising oceans threaten some entire nations, such as the Netherlands. The story of the little Dutch Boy illustrates the fact that this nation already depends on engineering to keep the sea out, such as the flood gates shown here. Rising sea levels and more intense storms will make it more difficult for Rotterdam and other Dutch cities to keep their heads above water, according to the same research that warned of floods in Shanghai.

An interactive map on Geology.com shows that a one-meter (3-feet) increase in sea level could demolish much of Brugge, the Hague, and Amsterdam. A catastrophic nine-meter (30-foot) increase would obliterate most of the Netherlands.

One of Bangladesh's many outlying slum communities. David Bathgate/Corbis

Rising oceans also threaten to swamp much of Bangladesh. A five-foot (1.5 meter) increase in sea level could submerge 22,000 square kilometers of the country, according to the United Nations Environmental Programme. Eighteen million people could be displaced by this flooding.

If the coastline of Bangladesh disappears, so too will much of the Sundarbans forest. This mangrove ecosystem provides habitat for Bengal tigers, mugger crocodiles and their prey, including chital deer and rhesus macaques. The wilderness draws tourists who contribute to the struggling economy of Bangladesh.

Maldivian Minister of Fisheries and Agriculture Ibrahim Didi signs a declaration calling on countries to cut down carbon dioxide emissions.Corbis

While the Netherlands and Bangladesh face disaster, the Maldives seem doomed to fulfill the destiny of Atlantis. The highest point in the Maldives rises seven feet and ten inches (2.4 meters) above the ocean. The average is only approximately five feet (1.5 meters).

Tourism makes up a tremendous portion of the Maldivian economy. Tourism income may help the nation resettle its citizens as the ocean claims the country. In 2008, the Maldivian government began diverting a portion of tourism revenues to purchase land where the nation's 300,000 residents might move after their homeland disappears, reported the Guardian.

In this 2009 photo, Maldivian Minister of Fisheries and Agriculture Ibrahim Didi signed a declaration calling on countries to cut down carbon dioxide emissions.