Millions of Americans lounge on beaches on Memorial Day, but many of those coastlines may become memories as the planet continues to warm. Global warming causes ocean water to expand, while glaciers melt and dump yet more water into the seas. The ocean now splashes 8 inches higher than 100 years ago, according to the National Climate Assessment released by the U.S. government earlier this month.

Rising sea levels have already begun to eat away at the shoreline of Miami Beach, above, while high tides flood the surrounding city even in calm weather.

"People in Miami Beach are living climate change," David Nolan, University of Miami oceanographer and meteorologist, told the Guardian.

Ninety percent of Miami sits less than 6 meters above sea level, according to a study published in Climatic Change. A 1-meter rise in sea levels would devour the beaches where sunbathers now show off their tans, along with nearly 20 percent of the city.

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The valuable oceanfront resorts and homes of Virginia Beach face an even graver threat than Miami Beach, according to that same paper in Climatic Change. More than 30 percent of the region lies 1 meter or less above sea level.

The local government implemented a $1.5-million plan to help protect the city from flooding, reported the Virginian-Pilot. To completely protect the city with a New Orleans-style flood wall would cost more than $130 million.

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Two playgrounds of America's wealthiest citizens face eroding beaches. Nantucket and Martha's Vineyard, two islands off the coast of Massachusetts, have some of the highest real estate values in the country. More of that expensive land washes away with every wave, according to the New England Aquarium. As the ocean gets deeper and storms become more intense, even more of Massachusetts could disappear than the 65 acres currently lost each year.

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The Hamptons of Long Island, N.Y, another elite oceanfront enclave, suffered the wrath of Superstorm Sandy in 2012. Four people died on Long Island, including one person whose body washed ashore on the beach of wealthy East Hampton, reported the Daily Beast.

Although the number of Atlantic hurricanes hasn't increased significantly in the past century, humans probably have caused an increase in the impact of extreme coastal events, like Sandy, warned NOAA scientists. The increase largely resulted from higher sea levels, which allowed storm surges to overwhelm beaches more easily than in the past.

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Numerous beaches along the California coast could lose millions in tourist revenue due to rising seas, according to another study published in Climatic Change. As beaches get narrower, visitors may snub some regions. Laguna Beach may be the worst hit, with an estimated $15 million in lost income. However, due to geographic features, storms may deposit more sand in other regions and increase the size of the beaches. These larger beaches may attract more tourists. Huntington City could see an increase of $16 million.

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Some Hawaiian islands are eroding faster than others, according to University of Hawaii geologists. During the past century, 78 percent of Maui's beaches suffered erosion at an average rate of 13 centimeters (5 in.) per year. Meanwhile, 52 percent of Oahu's beaches have eroded. Oahu's beaches only lost an average of three centimeters (1.18 in.) per year.

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Rising seas threaten to wash away the beaches of Cancún, Mexico, along with much of the the $3 billion tourist economy of the Yucatan Peninsula, according to the Union of Concerned Scientists. The beaches of Cancún already washed away once, in 2005 after Hurricane Wilma pounded the coast.

In 2006, tons of sand were dumped on the coast at a cost of $19 million, only to be washed away by Hurricane Dean in 2007. In 2009, another $70 million project restored 7 miles of beach. Approximately 8 percent of that sand had been washed away by 2010, reported the AP.

The sand quickly washed away partly because resort managers kept the beaches free of shrubs, grasses and vines that would naturally hold the sand in place. Tourists prefer glimmering expanses of white sand, a Spanish visitor to Cancún told the AP.

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The Mediterranean coast has been prized beachfront property for thousands of years. However, in the International Journal of Climatology, meteorologists suggested that some regions, including the southern European Riviera, may become uncomfortably hot during the peak summer tourism season by the end of this century. The meteorologists noted that spring and autumn may become better suited to a Mediterranean holiday.

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Some beach resorts could survive climate change, if they take action before the worst effects strike, wrote the authors of a study published in Ocean and Coastal Management. For example, the Gold Coast in Australia could continue to function as a tourist destination, even after a 1-meter rise in sea level. To do so, the city must build a sea wall of boulders, construct artificial reefs in the sea and replenish the sand lost from the beaches. However, a 2 to 5 meter sea level increase may prove unbeatable, even with early action.