Average sea levels are rising faster in China's coastal region than most other places in the world, affecting the coastal environment in various ways, the national marine authority said.

Instead of only threatening the relocation of communities and homes in the short term, rising seas are also causing damage to coastal soil and vegetation.

Chinese scientists are still studying and debating how long the trend of rising sea levels is going to continue. Sea levels started rising in the 1980s, and the trend is likely to continue, even accelerate, because of climate change, according to marine officials.

"China's coastal sea level on average rose by 3 millimeters a year from 1980 to 2015, higher than the global average," said Xiang Wenxi, deputy director of the National Marine Data & Information Service, a think tank affiliated with the State Ocean Administration.

In 2015, the average sea level along China's coast was 90 mm higher from 1975 to 1993, a benchmark for comparison, making it the fourth-highest since 1980, said the Bulletin on Sea Levels of China, issued by the administration on Tuesday.

Seas are rising because they absorb large amounts of heat caused by climate change, which has also accelerated the melting of land-based glaciers and the Arctic and Antarctic ice sheets, said Huang Lei, an engineer with the National Climate Center, last week. Since 1993, waters from melted land-based glaciers have made seas across the globe to rise 0.76 mm a year, and the melted ice sheets from the polar regions have caused them to rise by another 0.6 mm annually.

"The rise in sea levels has been forecast to continue and even accelerate in the future," Huang said. The national marine authority agreed with that assessment.

In the coming 30 years, Shanghai, a coastal metropolis with a population of more than 24 million, will see the sea along its coast rise by 75 to 150 mm, after rising 105 mm more than the benchmark level, the bulletin said. Moreover, Tianjin, another port city about 950 km north of Shanghai, could see its coastal waters rise by 100 to 195 mm.

"Rising sea levels will weaken the protective shield of sea dykes and harm some plants, decaying mangrove forests in the southern coastal regions," said Liu Kexiu, another senior researcher with the ocean administration's think tank. But he added that human activities have caused more damage to the precious mangroves.

More importantly, high seas aggravate storm surges, exacerbate flooding, erode shorelines, cause seawater invasion, inundate crops and homes, threaten livelihoods and even worsen marine disasters, said Liu, adding that the cities and people in the Pearl River Delta and Yangtze River Delta regions have suffered more than those in other regions.