SINGAPORE — As policymakers plan ahead in Tokyo, Osaka-Kobe and other major port cities in Japan, one of the most vexing questions they face is how much will the sea level rise in coming decades?
The stakes are high. By the 2070s, the number of people in the 136 big port cities around the world who are exposed to coastal flooding is projected to grow more than threefold, to around 150 million. If the predictions of scientists advising the United Nations on global warming are correct, port cities will have to endure more intense effects of climate change, including a rise in sea level, increasingly violent storms, and land subsidence as well as flooding, according to a recent study for the OECD, the Paris-based think tank of advanced economies.
The study, published in July, forecast that the value of flood-exposed economic assets in these port cities in the form of buildings, transport networks, utilities and other infrastructure could grow even more dramatically than population exposure, reaching $35 trillion by the 2070s, approximately 9 percent of projected global gross domestic product, up from 5 percent in 2005.
Bear in mind that the great port cities are often hubs of political power. They also include key financial and commercial centers in the United States and Europe, like New York, London and Rotterdam, as well as Asian centers like Tokyo, Osaka-Kobe, Shanghai and Bombay.
The OECD study found that the number of people in Tokyo at risk of coastal flooding by the 2070s would more than double, to just over 2.5 million from 1.1 million in 2005. This would rank Tokyo as the world’s 19th most exposed port city. In terms of economic assets at risk from the flooding, Tokyo would be number 8 in the world in the 2070s after Miami, Guangzhou, New York-Newark, Calcutta, Shanghai, Bombay and Tianjin, with infrastructure worth more than $1.2 trillion at risk, up from $174 billion in 2005. Among Japanese port cities, Osaka-Kobe would be next, at number 13 in the world, with nearly $970 billion in assets exposed to coastal flooding by the 2070s, while Nagoya would be number 17 with exposed infrastructure worth over $620 billion.
What is the precise threat from a rise in sea level to this accumulated wealth and power, and to international maritime trade that these port cities dominate? Summarizing available scientific evidence on global warming and its effects, the Intergovernmental Panel on Climate Change advising U.N. member states concluded late last year that the sea level would probably be somewhere between 18 to 59 centimeters higher by the end of this century, after a rise of 17 cm in the 20th century.
The IPCC projection for the 21st century took account of water expanding in the oceans as it warmed. However, because of uncertainty and incomplete research, the IPCC excluded estimated additions to the ocean mass from water as the ice sheets that cover Greenland and the Antarctic continent melt. Yet these are the sources able to produce the largest amounts of extra water flowing into the sea and adding to its volume. If the vast ice sheets and the glaciers on their perimeters melted completely, the sea level would rise by about 70 meters.
There have been a range of predictions from scientists about how fast ice sheet melting could occur as atmospheric temperatures increase more sharply in polar regions than most other places. But recently a team of American glaciologists reached a somewhat more definitive conclusion. In research published in the Sept. 5 issue of Science, they calculated how fast ice sheet glaciers would have to flow to raise sea level by a given number of meters, and then considered whether these flow rates were plausible or even physically possible. The latter consideration is relevant because in Greenland, and to a lesser extent in Antarctica, ice loss is limited by the number and width of rock-bound channels that form outlets for glaciers as they move, normally very slowly, from the land to the sea.
The team took account of a rise in sea level expected from ice melting on Greenland, Antarctica and the world’s smaller glaciers and ice caps, as well as thermal expansion of the seas and oceans. It concluded that the most likely scenario was a total sea level rise of approximately one meter to two meters by 2100.
If these glaciologists are right, what will the impact be? The Tyndall Center for Climate Change Research in Britain has warned that Asia — because of its vast coastline, many mega deltas, big port cities and dense population — will be by far the region most seriously affected by a rise in sea level of this order of magnitude. It has calculated that a one meter increase in sea level would inundate more than 800,000 square km of land in Asia, displacing over 100 million people and causing a potential loss of nearly $450 billion in GDP.
Of course, the impact would vary from country to country, depending on its geography and ability to protect its urban centers, people and assets in low-lying coastal zones. Japan — with its wealth, knowledge and resources — is well-placed to do this. It has six port-cities spanning river deltas — Fukuoka- Kitakyushu, Hiroshima, Nagoya, Osaka-Kobe, Sapporo and Tokyo. Even the most exposed could be better protected from the rising sea level.
However, a couple of years ago, the World Bank commissioned a group of specialists to assess the consequences of sea level rise in the range of 1 to 5 meters for 84 coastal developing countries that get loans or technical assistance from the bank. Many of them do not have the resources to cope with rises in sea level and other climate-induced change on the scale being forecast by scientists. The specialists for the World Bank used high-resolution digital mapping to estimate the impact on each country’s land, population, agriculture, cities and GDP.
Among the 84 countries surveyed were 12 in Southeast Asia and Northeast Asia that have low-lying coasts facing the sea — Brunei, Cambodia, China, Indonesia, Malaysia, Myanmar, North Korea, the Philippines, South Korea, Thailand, Taiwan and Vietnam. The researchers concluded that within this century, hundreds of millions of people in the worst affected of the 84 countries are likely to be displaced by sea level rise, and that the associated economic and ecological damage will be severe for many.
In East Asia, Vietnam — the world’s 12th most populous nation — will be hardest hit. If the sea level were to rise by 5 meters, 16 percent of Vietnam’s land area would be inundated and 35 percent of its over 84 million people forced to move, resulting in a GDP loss of around 37 percent. Even a rise of one meter in the sea level would displace nearly 11 percent of Vietnam’s population and wipe out 10 percent of its economy.
Other Southeast Asian countries that could be seriously hurt in terms of land loss, population displacement, reduced GDP, and impacts on urban centers and agriculture include Thailand (current total population over 64 million), Indonesia (over 222 million), the Philippines (over 82 million), Malaysia (over 25 million) and Cambodia (over 14 million).
In relative terms, China was among the least affected of the 12 East Asian economies covered in the World Bank study, which was published last year. But in absolute terms, the damage would still be significant for the world’s most populous nation. It would be concentrated in low-lying areas along China’s highly industrialized and urbanized eastern seaboard.
The OECD report found that 15 of the top 20 port cities ranked in terms of population exposed to coastal flooding from climate-linked storm surge and rises in sea level in the 2070s would be in Asia, with four of them in China — Guangzhou, Shanghai, Tianjin and Ningbo. By then, these four cities are projected to have a combined flood-exposed population of nearly 23 million.
The report said that 13 of the top 20 port cities with assets exposed to coastal flooding in the 2070s would be in Asia, six of them in China – the four mentioned above, plus Qingdao and Hong Kong. The combined value of their flood-exposed assets is forecast to be almost $9,200 billion, with $1.164 trillion of that amount in Hong Kong.
One of the conclusions of the OECD report is that the likely impact of climate change and a rise in sea level needs to be integrated into both coastal flood risk management and urban development strategies of vulnerable countries. Advance planning and investment are required because big defense projects, like the mechanical barriers near the mouth of the River Thames to protect greater London and its port zone from tidal and storm surges, typically take 30 years or more from planning to completion.
Michael Richardson, a former Asia editor of the International Herald Tribune, is a security specialist at the Institute of South East Asian Studies in Singapore.