assume that such scene indicates accelerating coastal erosion. There are also reports on salt damage due to the seawater that enters into fields, damaging crops.

On one hand, such salt damage can be attributed to the nation’s societal change; increasing population has led to the expansion of residential areas and farming lands into flood-susceptible areas. However, it is estimated that the acceleration of global warming will further exacerbate the said damage.

### d. Changes in the habitat conditions of plants and animals

Animals and plants, who are constituents of ecosystems, are sensitively reacting to global warming. There are many reports from all over the world on various changes in their habitat that are attributable to global warming.

The Arctic Circle, which is considered as the area most vulnerable to global warming in the world, facing the peril of the extinction of polar bears. Polar bears depend on seals for food. They hunt seals by capturing them, sneaking up through an ice hole to breathe. Fat from seal meat stored in the body makes it possible for bears to survive. Loss of sea ice as a result of global warming would endanger polar bears because they will not be able to hunt seals easily. Actually, the results of a survey on the average weight of polar bears living in Hudson Bay, Canada, show that they have lost weight in the last few decades, from an average weight of only 230 kg as of 2004, compared to 295 kg in 1980. The weight of 230 kilograms is considered to be close to the minimum level that allows polar bears to maintain the reproductive ability. There have also been reports of polar bear deaths attributable to melting ice. The bears had been forced to swim for long distances and have died due to exhaustion. In 2006, the World Conservation Union (IUNC) classified polar bears into the Red List of Threatened Species as “Vulnerable (VU).”

Another example is coral-reef bleaching. Reports of coral bleaching (coral bleaching is the whitening of coral colonies due to the loss of symbiotic zooxanthellae from the tissues of polyps) have been frequently heard from various places around the world. The ecological significance of coral reefs is remarkable, as they serve not only as habitats and egg-laying sites for around 4000 species of fish, but also as natural breakwaters that protect people's homes in coastal areas. Among various factors known to be responsible for coral bleaching, one of the most serious ones recently reported is a stress caused by rising seawater temperature. It has been discovered that during the 1998 El Nino event, which was the severest one in history, as much as 16% of the global coral reefs died or were seriously damaged. Scientists predict that the combined effects of global warming and El Nino, causing further rise of seawater temperatures, could result in coral bleaching which will become much more common. In addition, there is a report warning that accelerating ocean acidification caused by the increase in $ CO_{2} $ uptake will make it difficult for corals to form a hard protective skeleton of calcium carbonate, and will possibly hamper the growth of corals. The IPCC AR4 WG1 report estimates that projections based on SRES scenarios give reductions in average global surface ocean pH16 of between 0.14 and 0.35 units over the 21st century, adding to the present decrease of 0.1 units since pre-industrial times.

Global warming also causes changes in flora/fauna habitat locations. In Japan, stakeholders are paying close attention to the recent phenomenon of the northward expansion of habitats of

Coral near Akajima Island of the Kerama Islands, Okinawa Prefecture

Photo: courtesy of by Akajima Marine Science Laboratory

Figure 1-7 Northward expansion of habitats of Papilio memnon Linnaeus

Note: Figures indicate calendar years. Small letters from “a” to “l” indicate twelve cities and locations where temperature analysis was conducted. Source: “Correlation between the expanding habitats for Papilio memnon Linnaeus and global warming” written by Masahiko Kitahara et al and published through the journal “Butterflies and Moths” issued by the Lepidopterists’ Society (52, 2001).