Rising temperatures + melting glaciers = higher seas levels. With those surging waters comes the potential for lower-lying land areas around the globe to be washed out, according to climate scientists. They're not just talking about a handful of backwater locales already rendered nearly vacant by the invisible hand of modern progress. If a pair of European researchers is right, some of the most important historic, architectural, cultural and religious destinations on the planet may eventually be lost at sea.
First, the numbers: Sea levels are expected to rise by as much as 7.5 feet (2.3 meters) per every 2 degrees Fahrenheit (1 degree Celsius) that global temperatures increase, according to researchers at the Potsdam Institute for Climate Impact Research. With average surface temperatures possibly ticking up by as much as nearly 9 degrees F (5 degrees C) by 2100, that would mean an accompanying sea-level jump of about 30 feet (9 meters) [source: Montaigne].
If warming rates continue to rise, researcher Ben Marzeion of the Institute for Meteorology and Geophysics and the Potsdam Institute's Anders Levermann say that as many as 136 designated locations deemed world heritage sites by the United Nations could be washed into the sea in the next 2,000 years. While that may seem like a long time, some of the current U.N. world heritage sites are older than 2,000 years [sources: CBC News, Marzeion and Levermann]. Let's take a look at some structures that could be affected, from the remains of a 3,000-year-old civilization to a torch-toting monument to American freedom, in chronological order.
The more-than-3,000-year-old city of Nessebar dots a rocky Bulgarian peninsula on the Black Sea. After being settled by Thracians during the Bronze Age, the city was later colonized by Greeks in 6 B.C.E. It stands as an informative testament to the various civilizations that inhabited this narrow stretch of land, with archaeological and architectural highlights including a Greek acropolis, a temple to Apollo, a ninth-century basilica and a Middle Age fortress [source: UNESCO].
As if the wear and tear that comes with hosting residents – and, more recently, tourists – for more than 30 centuries wasn't enough, rising seas have already claimed about one-third of the ancient city's original land mass. Today, Nessebar stands at about 0 to 59 feet (18 meters) above sea level [sources: UNESCO, National Institute of Immovable Cultural Heritage].
One of the world's most unique urban settings, the Italian city of Venice consists of 118 islands over a lagoon, many of which are linked through a series of canals. Let Florence have all the good art museums; this city on the water is a living, breathing monument to the Byzantine, Gothic and Islamic influences it's seen over more than 1,500 years [sources: UNESCO, Approach Guides].
From its low perch on the Adriatic Sea in Italy's northeast corner, Venice is no stranger to flooding. But these events are becoming more extreme -- as much as 70 percent of the city was underwater during a flood in 2013 -- and climate scientists attribute that to rising sea levels. Meanwhile, research shows that Venice's elevation is sinking by about 0.09 inch (2 millimeters) each year while sea levels rise by 2 millimeters. City workers are scrambling to set up a series of seawalls to lessen the flood damage [sources: Berg, Knight].
If you've seen the 2008 black comedy "In Bruges," then you probably already know that this scenic Belgian town's stunning array of Gothic architecture makes a good backdrop for a dark buddy film about two hapless hit men who take in the sights while awaiting a call from their foul-mouthed, easily irritated boss. The center of the city (spelled "Bruges" in English and "Brugge" in Dutch) just so happens to be a charming medieval historic settlement that served as the launching point for Flemish primitive painting. The first mention of the city was in ninth century. The 401-foot (122-meter) Church of Our Lady is among the world's tallest brick buildings, as well as home to Michelangelo's "Madonna and Child," the only one of the artist's sculptures to leave Italy during his lifetime [sources: UNESCO, Codart].
Originally inhabited by natives of the Bantu tribe and later in the 10th century by Arab settlers, the island of Mozambique (off the coast of the African country of Mozambique) rose to prominence as a Portuguese trading outpost on the route to India. Today, it's known as much for its enchanting beaches, spectacular coral reef and vibrant blue waters as it is for its centuries-old fortress and various religious buildings. The city is considered a strong example of architectural unity, given that islanders have relied on the same techniques and materials since the 16th century [sources: UNESCO, Lonely Planet].
Climate change not only threatens the island, its people and its architecture, but also many of the creatures that call the waters surrounding Mozambique home. Sea turtles, for example, time their reproduction cycles to sea temperatures that ensure an adequate ratio of male and female offspring. The higher the temperature, the more likely a turtle is to produce females. Scientists fear that changes in water temperatures will throw off the cycle, leading to a scarcity of males and choking off further reproduction [sources: IOP Science, Warne].
It's hard to imagine the United Kingdom's capital city without the Tower of London, the formidable fortress erected by William the Conqueror in 1066. Dominating the British skyline along with Big Ben, St. Paul's Cathedral and the London Eye, the Tower is actually an entire castle that over the years has functioned as everything from a military barracks, execution site and prison to the home of England's crown jewels [source: PBS].
The tower's location along the Thames River was intended to strike a warning pose to would-be invaders during the 11th-century Norman conquest. These days, its near-sea level positioning makes the fortress vulnerable to climate change, according to researchers [sources: UNESCO, IOP Science].
Nestled along the English Channel in Normandy at the mouth of the Seine estuary, Le Havre was a small fishing village before King Francois I transformed it into one of France's biggest harbors in the early 16th century. The city remained a thriving trade port until World War II, when it was violently bombed [sources: World Port Source, UNESCO].
Le Havre was meticulously reconstructed between 1945 and 1964, to mirror the town's original pattern while also making room for more modern urban planning and construction techniques. UNESCO called the remade city "a landmark of the integration of urban planning traditions."
It was originally constructed on top of drained marshes, and the rebuilders had planned to place it on a reinforced concrete platform roughly 11 feet (4 meters) above ground. However, that plan was scrapped due to postwar limits on iron and cement, and Le Havre remains subject to flooding, which is only expected to increase as sea levels rise [sources: UNESCO, IOP Science].
The last Cuban city founded by Spanish conquistadors in 1519, Old Havana retains much of its original character as both a large shipping port and military defense installation while offering visitors a vivid slice of life in the Caribbean's largest metropolis. The old city is tied together by five large plazas, each of which maintains its own character and personality. Old Havana features an array of Baroque and neoclassical architecture, exemplified by the private colonial mansions that line quiet side streets just off the main thoroughfares [sources: UNESCO, Rough Guides].
La Habana Vieja, as it's known to locals, is also home to some of the country's best museums and its lively arts scene. Thanks to a restoration initiative partially funded by the United Nations, the decaying city is getting a facelift and is poised to modernize its urban core, while retaining its old-world charm. That, of course, depends on Old Havana – as low as 7 feet (2 meters) above sea level at certain points – staying dry [sources: UNESCO, Rough Guides, Tablada de la Torre].
Lady Liberty stands tall at the mouth of the New York Harbor welcoming visitors, immigrants and residents to America's largest city as a proud symbol of freedom and democracy. Dedicated in 1886, the 305-foot (93-meter), 450,000-pound (204,117-kilogram) statue was a gift from the people of France as a sign of friendship with the U.S. and in recognition of its successful creation of a democratic society.
The Statue of Liberty was created by the French sculptor Frederic-Auguste Bartholdi out of sheets of hammered copper, and the steel framework was designed by French engineer Alexandre-Gustave Eiffel, who later designed the Eiffel Tower, The torch-wielding statue was the first thing millions of immigrants saw as they approached nearby Ellis Island and remains one of the world's best-known landmarks [History.com].
Superstorm Sandy left Liberty Island (the home of the statue) 75 percent underwater in 2012 – the only thing showing was Lady Liberty and her pedestal [source: Rizzo]. That gives you a foretaste of what could happen permanently in the future if climate scientists are correct.
Established in Iran in 1844, the Baha'i faith preaches that the founders of the world's main religions -- Abraham, Moses, Jesus, Buddha, Muhammad and Krishna -- are "divine messengers" tapped to disclose revelations of one God, and that their religion's founder, Baha'u'llah, is the latest divine messenger. Despite (or because of) this accepting approach to all faiths, Baha'i leaders and followers faced persecution from the outset, particularly in their native country [sources: Baha'i Topics, UNESCO].
Viewed as heretics to the Islam religion, roughly 20,000 Baha'i followers – including a prophet called the Báb – were killed across Iran in the mid-1850s. After wandering Turkey, Iraq and Egypt for 15 years, Baha'u'llah came to Western Galilee in 1868 as a prisoner. He remained in the area for the last 24 years of his life, drafting and compiling the scriptures that now serve as the religion's foundational texts [sources: Baha'i Topics, UNESCO].
Two of the Baha'i faith's most important holy places -- the Shrine of Baha'u'llah in Acre and the Shrine of the Báb in Haifa – were erected in the 1950s in what's now Israel, and are visited by thousands of Baha'i pilgrims each year. Still, the twin shrines and their meticulously kept meditation gardens face the threat of rising waters from the nearby Mediterranean Sea [sources: UNESCO, IOP Science].
The newest landmark on the list, the Sydney Opera House was completed in 1973 after 16 years of work and is considered a masterpiece of 20th-century architecture. The performing arts center is easily Australia's best-known structure, thanks to the large, white-tiled shells that form the building's roof and the glass facades that face the Sydney Harbor [source: Australian Government].
Like many of the world's wonders at risk, the opera house's waterfront location leaves it at the mercy of climate-change threats. The building is just about 11 feet (3.5 meters) above sea level, and climate scientists fear that the nearly 600 piers propping it up could be damaged by rising salt water and storm surges, as well as higher air temperatures and humidity and extreme weather events [source: Battenbough].
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