Most of the world’s coastal cities were established during the last few millennia, a period when global sea level has nearly remained unchanged. Since the middle of 19th century, sea level has been rising, caused primarily by two factors related to global warming (the added water coming from the melting of land ice and the expansion of sea water as it warms). It is suggested that the rate of sea level rise is likely to increase during the 21st century, although there is considerable controversy about the likely size of the increase. As a result of sea level rise, the coastal erosion and sea flooding in coastal cities are becoming more and more severe. Meanwhile, coastal and estuarine ecosystems have been, and still are, heavily influenced by the human activities, such as the pollution discharge and habitat loss. This coastal pollution and its impacts have resulted in a number of environmental issues including the enrichment of enclosed or partially-enclosed waters with organic matter leading to eutrophication, pollution by chemicals such as oil, and sedimentation due to land-based activities or sea level rise.