Scenes of huge tidal waves crashing into skyscrapers and washing away entire cities may be popular Hollywood devices, but they still arguably evoke fear in everyone.
Disaster movies like The Day After Tomorrow and recent blockbuster 2012 bring these dramatic fantasies to cinematic life, but scientists have warned the reality could prove just as scary.
Sea levels across the world are rising slowly every year, a fact that is creeping off the pages of numerous science reports and environmental awareness campaign leaflets into people's daily consciousness, particularly those living on the eastern and southern coasts of China.
One such resident is Tang Jun. The communications manager for chemical manufacturer Bayer Group has always been proud of the view from his office on the 19th floor of Citigroup Tower in Shanghai.
Being among the gleaming skyscrapers overlooking the world famous Bund also offers the perfect spot to keep an eye on the water levels of nearby Huangpu River, the city's largest river, which separates the Pudong and Puxi districts. The waterway also connects the Yangtze River and East China Sea.
"As it is November, the water level is relatively low at the moment and a few meters of beach are exposed on the riverbanks," said Tang, 33. "But in the summer, when Shanghai was hit by a typhoon, the water rose tens of centimeters higher than its banks and flowed onto the road. For most residents in Shanghai, the sea level rise is a remote thing, for us it happens downstairs. But we still cannot do anything to stop it. All my colleagues and I can do is save energy and improve energy efficiency on our production lines and in our office."
Tang is far from the only one observing the changes in China's costal regions, so too are the nation's marine authorities. However, their findings and predictions are unlikely to cheer residents and business leaders.
In a report last year, the State Oceanic Administration showed the country's overall sea level had risen 92 mm in the last 30 years, while the average offshore surface temperature and coastal region temperature had increased by 0.9 C and 1.1 C respectively.
Last year, the seas around China reached their highest levels in 10 years, 14 mm higher than in 2007 and 60 mm more than the average for the last 50 years, the report said. The administration also forecasts that, over the next three decades, sea levels will continue to rise and could even be up to 130 mm higher by 2039.
Global warming, which is causing seawater thermal expansion - when the seas increase in volume due to higher temperatures - and glacier melting, is the cause of the sea level rise, said the report. Water extraction projects and ongoing major construction are also contributing as they cause surface subsidence, which effectively means the city is sinking.
"The deltas of the Yangtze River, Pearl River and Yellow River, as well as the costal areas of Tianjin municipality, are the areas in China most at risk from rising sea levels," said the report, which warned that a continued rise would "accelerate storm surges, coastal erosion, saltwater intrusion, soil salinity and other marine disasters".
Shanghai, which lies in the Yangtze River Delta, is in serious danger from the rising waves, according to the State Oceanic Administration, which estimates that the financial powerhouse will see a higher-than-average increase of 98 to 150 mm during the next 30 years.
Residents witnessed a preview of the impending disaster in August, when a violent rainstorm brought the city to a standstill.
The downpour began on the morning of Aug 25 last year and, within just one hour, Xujiahui district was battered by 110 mm of rain, while municipal monitoring sensors showed more than 100 roads in the city's downtown areas were completely submerged.
One resident, after leaving home for work, was reportedly trapped in his car by the deluge and only rescued 24 hours later.
Kang Jiancheng, a professor at Shanghai Normal University, said he remembers leaving work at 10 pm that day and found the floodwaters were still up to his knees.
The 66-year-old has studied glacial melting at the Polar Research Institute of China, a project under the State Oceanic Administration based in Shanghai, since 2005. He is leading a team looking at the influence of sea level rises on Shanghai.
He said the study divides the city - which has a population of 18.5 million and a downtown population density of 22,700 per sq km, three times that of Manhattan, New York - into five areas, from the most vulnerable up to the most resistant.
Primary research has shown that the areas along the Huangpu River, including Pudong New Area - the financial heart of the city and home to the municipal government, many luxury hotels and several large shopping malls - is the most exposed to the risk of rising sea levels, he said.
The southeastern districts of Fengxian and Nanhui contain the areas least likely to be affected, suggested initial findings.
"When Huangpu River surges, you can easily see that the water is higher than a pedestrian. Any construction along the river depends on the dike holding," said Kang.
Shanghai officials started work on a 50-km floodwall to run along the river in 1956. Reinforcements have continued ever since, with the dam expanded from just below 5 m in 1963 to 6.4 m last year. It now also runs 208 km long.
Municipal authorities also plan to further raise the vital flood defense to more than 6.7 m, as well as strengthen it to meet the threat extreme weather conditions and storm surges - when water is pushed toward the shore by strong winds - that scientists warn will become more regular thanks to climate change.
"Shanghai has to consider all extreme scenarios against the backdrop of climate change when it comes to its floodwall," said Kang. "A rise of 100 mm in 30 years might seem very small for most people, but it would be disastrous in the event of a storm surge or typhoon."
Besides reinforcing the floodwall, Kang also suggested that the municipal government improve the city's drainage works.
Shanghai's sewer system can drain 36 mm of rainfall per hour, which was designed based on the average amount of rain in Shanghai, according to Ma Yuandong, director of the Shanghai Municipal Drainage Administration. But in the event of extreme weather, like the storm in August last year, the system is likely to be overloaded, said Kang.
Urban planning experts have explained that revamping Shanghai's drainage network would not be easy. Construction of a new pump station would costs hundreds of thousands of yuan, while any project would involve relocating residents from a dense downtown area, said Ma.
"Shanghai has a very low altitude, about 3.5 m above sea level," said Kang. "If the drainage works cannot be improved, it is possible Shanghai could see a similar tragedy like the one witnessed in New Orleans in 2005."
Shanghai, which will host the 2010 World Expo, has latched onto the opportunity to boost awareness of green and low-carbon growth with its chosen theme, "Better City, Better Life".
Officials say the expo grounds will realize zero carbon emissions, the greenhouse gases that are aiding global warming, while surrounding areas will record only low carbon emissions.
To hit the target, 1,000 new shuttle buses powered by renewable energy went into service this month, and a 400-km subway system is to be completed ahead of the expo launch in May.
Between 1997 and 2008, Shanghai has converted 5,975 coal-fired boilers to use clean energy, such as natural gas, creating a 660-sq-km "coal-free zone", said the municipal authority. Officials have also shut down several small and inefficient coal plants with a combined total capacity of 695,000 kilowatts within the expo site.
Shanghai has incrementally tripled its investment in green energy and programs to 42 billion yuan ($6 billion) since successfully bidding to host the event in 2000.
Their efforts will not only benefit the predicted 70 million visitors to the expo, but also leave a green legacy for the city's 18 million citizens.
(China Daily 12/02/2009 page7)