that Anopheles, transmission vectors of Plasmodia, become active at a temperature of $ 22^{\circ} $ C or higher. Malaria has been eradicated in Japan, but due to accelerating global warming, Japan will be closer and closer to potential malaria-vulnerable regions again.

Dengue fever is also a vector-borne infectious disease transmitted via mosquitoes living in hot regions, such as Aedes aegypti and Anepheleles. Each year, about 100 million people around the world contract this disease, and about 250,000 of them are estimated to develop life-threatening dengue hemorrhagic fever. Children in the tropical and subtropical regions are especially vulnerable to the menace of dengue fever. Historically, Southeast Asian countries and Caribbean countries used to be the center of

Aedes aegypti sucking human blood

Photo: courtesy of Hitoshi Kawada, Institute of Tropical Medicine of Nagasaki University

the dengue infection, but the disease has been expanding recently to reach the southern part of China, South Pacific countries and South America. In tourist-abundant Hawaii, dengue fever spread in 2001 and 2002, registering 122 patients. Like malaria, dengue fever could also be a new menace to Japan because of global warming.

Also, due to the expanding habitats of vector mosquitoes, there is a concern that Africa-centered infectious diseases such as Rift Valley Fever and West Nile Fever could become widespread in other regions.

Prevalence of infectious diseases is dependent on multiple factors such as residential environment and public health, but it is necessary for the international society to understand that global warming could cause infectious diseases to spread and it is necessary to give attention to this matter.

### 4. Impact on Culture

Quantitative and qualitative changes in ecosystem services could have not only material or physical impacts but also societal and cultural impacts.

Lake Suwa in Nagano Prefecture is known for its unique natural phenomenon of a frozen upheaval of lake water surface, called “omiwatari.” It is caused by repeated expansion and contraction of ice as a result of ups and downs of temperature. Traditionally in Suwa City, a holy ceremony to appreciate “omiwatari” is held where the chief priest and a representative of the parishioners of Yatsurugi Shrine (in Suwa City) identify and certify the formation of “omiwatari.” During the ceremony, cracked water-surface conditions are observed, and the results of the observation tell the year’s fortunes, including weather forecasts, crop harvests and even the fortunes of society. As a result of warm winters, Lake Suwa has frequently missed “omiwatari” in recent years.

Cherry blossoms tell Japanese people the arrival of the spring season, and have a long history of cultural significance to the Japanese, who have celebrated this flower since ancient times. Cherry blossoms appear in many old Japanese poems. One of the six great poets in the early Heian era, Ariwara no Narihira, wrote, "If there were no cherry blossoms in this world, how much more tranquil our hearts would be in spring." (In other words, it is because of the unpredictability of the blooming and falling of the cherry blossoms that spring is such a time of agitation and excitement.) Recently, global warming and other causes have an effect to the season of this best-loved flower. For the past fifty years, since the Japan Metrological Agency started phonological observations in 1953, the official “blooming” announcement day has come earlier and earlier, and today, cherry blossoms start blossoming about

“Omiwatari” of Lake Suwa

Photo:courtesy of Suwa CityMuseum

4.2 days (national average) earlier than fifty years ago.

It has also been reported that some areas in Kyushu show an extraordinary phenomenon in which a temperature rise does not necessarily induce earlier blooming, and some researchers have pointed out that hot winters tend to detune blooming. Cherry blossoms have an internal mechanism that triggers blooming after a certain minimally-required period of dormancy in winter, and they cannot bloom when dormant low-temperature winter days are too few. If the recent rising temperatures detune the blooming of cherry blossoms to a large extent, and should it result in cherry blossoms not necessarily blooming in spring, it would upset Japanese people since the cultural significance of cherry blossoms is now closely related to the spring