Professor of the Center for Water Environment Studies, Ibaraki University

　

　

 Effects of global warming on the ocean and coastal areas are now our major concern. Particularly, the resultant rise in the sea level and the effects on the frequency of typhoon occurrence are estimated to produce undesired effects on the coastal areas. The Intergovernmental Panel on Climate Change (IPCC), a scientific evaluation organization of the United Nations, released the 3rd report in 2001. This report predicts that the average temperature will increase 1. 4 to 5. 8 degrees centigrade and the sea level will rise 9 to 88 cm by 2100. This paper provides an overview of the contents described in this report, specifically the effects of the temperature increase and the rise in the sea level on the ocean and coastal areas.

　

 The major effects of global warming on the ocean include the increase in the seawater temperature, rise in the sea level, decrease in an area of sea ice, change in the seawater salinity, change in the sea-wave phenomena, and change in the conditions of the ocean circulation. These effects became manifest in the 20th century: the average sea level rose 10 to 20 cm, an area of sea ice in the Arctic Ocean decreased 10 to 15% since 1950, and so forth.

　

　

 Physical changes occurring in the ocean affect the biological process. If the E1 Nino event occurs frequently and the seawater temperature increases, plankton and fish eggs will decrease markedly, producing bad effects on fish, sea mammals and sea birds. Although it is known that the catch of sardine and salmon stocks changes in a cycle of about 30 years, the large-scale alteration of fish species now being experienced is thought to be closely associated with the state change (regime shift) of the ocean.

 If fisheries are adversely affected by the change in the fish stocks, the catch of fish must be controlled internationally to ensure sustainable fishery. Fish culture is one approach to this problem. Although about 30% of the catch is now fish raised by fish culture, fish culture itself is affected by the catch of herrings and sardines that are used to feed fish being raised by fish culture.

 The rise in the sea level and the climate change make the coastal area more vulnerable to inundation, coastal erosion and intrusion of saltwater. The climate change also changes the frequency of typhoon occurrence, which in turn results in a stronger impact on the coastal area. In the island countries in the Asia-Pacific region, the population is concentrated along coastal areas and in low lands along rivers, and the risk of people living in such areas being hit severely by natural disasters is increasing. Furthermore, the cities and infrastructures in such coastal areas will be impacted heavily if natural disasters occur. Another point to be noted is that the climate change may aggravate the environmental problem in overpopulated cities. Effects on the coastal areas in higher latitudes should also be noted though they have until now not been discussed seriously. If an area of sea ice decreases, the sea waves will increase the force of erosion, and the coastal erosion will develop further. Frozen ground and the ice on the ground will thaw, and they may produce another erosion effect.

 Coral reefs, wetlands, mangroves, and other coastal ecosystems are also affected by the rise in the sea level, increase in the seawater temperature, and change in the frequency of typhoons. Coral bleaching has continued to develop for the past 20 years, and it is estimated that it will develop further, due to the change in the seawater temperature.

　

 The author et al. is making a quantitative evaluation of the effects on the Asia-Pacific region, while using data provided by the IPCC as reference data. Our evaluation covers the entire area of Asia-pacific region, the Arabian Peninsula and the eastern part of Africa in the east-west direction and the majority of the Russian continent, Australia, New Zealand, and other areas in the north-south direction.

 We assumed the scenario that the average sea level increases one meter in 2100 from the present level. We calculated the flood tides caused by all typhoons recorded in the past 40 years and defined maximum values for each coastal area as the sea level at flood tide. Areas that may be inundated or submerged and the populations in these areas were identified through calculations, assuming that they are inundated or submerged if their heights above sea level are lower than the sea level at high tide or lower than the sea level calculated based on the total height of high tide and flood tide.

 Areas that may be submerged or inundated are distributed in the Mekong Delta in Vietnam, the delta area at the river mouth in the southern part of New Guinea, Bangladesh, and the coastal areas of China (at the mouth of the Chang Jian River and in other areas). More than 10% of the population in each nation of Vietnam, Cambodia, Brunei, Bangladesh, etc., will be affected by inundation or submergence. The coastal areas of the island countries in the southern Pacific will also be affected greatly (Figure 1).

 The total land area of the Asia-Pacific region is about 65,000,000 m², and the total population was about 3. 8 billion in 1994. In 2100 the total population is estimated to reach about 7. 8 billion. The area of the land that becomes lower than the sea level at high tide is 310,000 km²(0.48% of the total land area), and the area of the land that becomes lower than the sea level when high tide occurs concurrently with flood tide is 610,000 km² (0.94% of the total land area). If the sea level rises one meter, 310,000 km² and 610,000 km² will increase to 620,000 km²(0.95% of the total land area) and 860,000 km²(1.32% of the total land area), respectively. This means that the flood tide causes the affected area to increase 250,000 km² if the sea level rises one meter(Figure 2).

 The population in the land area that becomes lower than the sea level at high tide is 47 million (1.21% of the total population) and the population in the land area that becomes lower than the sea level when high tide occurs concurrently with flood tide is 207 million (5.33% of the total population). These land areas are vulnerable to flood tide and other disasters. When the total population reaches about 7.8 billion by 2100, the population of 47 million will reach 200 million and the population of 207 million will reach 456 million. This means that the flood tide causes the number of affected people to increase by 249 million if the sea level rises one meter. Global warming is a problem that has a serious impact on the safety and the living conditions of people in the coastal areas of nations in the Asia-Pacific region.