September 16, 2004

The latest global warming projection by using the Earth Simulator has been completed
-Increase of hot weather and heavy rain in Japan due to global warming-



Center for Climate System Research, University of Tokyo (CCSR)
Professor :Akimasa Sumi
Professor : Masahide Kimoto
National Institute for Environmental Studies
Senior Researcher: Seita Emori
Senior Researcher: Tohru Nozawa
Frontier Research Center for Global Change,
Japan Agency for Marine-Earth Science and Technology
Group Leader: Seita Emori
(Reported at Press Club in Ministry of the Environment, Press Club in Ministry of Education, Culture, Sports, Science and Technology and Press Conference in Tsukuba Science City)
Outline

The joint research team of the Center for Climate System Research of the University of Tokyo (CCSR), National Institute for Environmental Studies (NIES), Frontier Research Center for Global Change (FRCGC) of the Japan Agency for Marine-Earth Science and Technology (JAMSTEC) conducted global warming experiment toward the year 2100 by using the Earth Simulator, the fastest vector-parallel computer in the world. Its results have the highest resolution currently in the world for projections on the global atmosphere and ocean phenomenon. In this experiment, results of the overall trend on climate change at global scale were similar to the estimations so far obtained. What is new is that in this projection, more detailed analysis was conducted on climate predictions of summer in Japan toward 2100. The result suggested that the temperature and the precipitation would increase steadily and along with the global warming, the number of very hot days in summer and frequencies of heavy rain would increase steadily. It is expected that through further analysis, further findings on climate changes at regional scale can be obtained.

This research was conducted on "Project for Sustainable Coexistence of Human, Nature, and the Earth" launched by Ministry of Education, Culture, Sports, Science and Technology(MEXT). The model used for the projection experiments is a high-resolution coupled ocean-atmosphere climate model (K-1 model) developed by CCSR,NIES and FRCGC.
   

1. Background


Using supercomputers, various research institutes in the world have conducted projections on global warming caused by increase in greenhouse gasses such as carbon dioxide in the atmosphere. These projections are carried out by segmenting the atmosphere and the ocean into grids and then making approximations of physical law. The grid size denotes a resolution and a higher resolution requires a larger-scale computer resource. Conventionally, projections so far conducted could be carried out in only about 300km resolution for the atmosphere and 100km for the ocean. Yet by using the Earth Simulator which is the largest-scale supercomputer in the world, we could successfully conducted the projections on global warming with the resolution of 100km for the atmosphere and 20km for the ocean, which is currently the highest resolution in the world. This research environment allowed us to study climate changes in more detail from the point of spatial distribution.

2. Outline of projections

For the period of 1900 to 2000, projection was conducted with variations of the observed greenhouse gas concentrations. For 2001 to 2100, projection was conducted on two of Intergovernmental Panel on Climate Change (IPCC) future scenarios. One is Scenario "A1B" based on the assumption that a future world will have more global economic growth (the concentration of carbon dioxide will be 720ppm in 2100). The other is Scenario "B1" based on the assumption that a future world will have global green economy (the concentration of carbon dioxide will be 550ppm in 2100).

3. Result of global scale


The results of the overall trend on climate change at global scale were similar to the estimations so far obtained. The global-mean temperature during the period of 2071 to 2100 increased by 3.0°C in Scenario B1 and 4.0°C in A1B compared to that of 1971 to 2000. Similarly, the precipitation increased by 5.2% in B1 and 6.4% in A1B (Note 1). In the geographic distribution, temperature rise is larger at high latitudes in the Northern Hemisphere and it is larger on land than on sea (Figure 1).



4. Summer in Japan


According to the results, the daily mean temperature of summer (June, July and August) in Japan during the period of 2071 to 2100 increased by 3.0°C in Scenario B1 and 4.2°C in A1B compared to that of 1971 to 2000. Similarly, the daily maximum temperature in Japan increased by 3.1°C in B1 and 4.4°C in A1B. The precipitation in summer in Japan increased steadily due to global warming (the annual average precipitation increased by 17% in Scenario B1 and by 19% in Scenario A1B during the period of 2071 to 2100 compared to that of 1971 to 2000). The reason seems that in relation to the temperature rise in the tropical Pacific Ocean, a high-pressure anomaly area appears to the south of Japan, bringing warm and humid southwest wind as well as a low-pressure anomaly to the vicinity of Japan. Then, in relation to the temperature rise in the continent, a high-pressure anomaly up in the air is caused to the north of Japan, blocking the move of seasonal rain front toward the north (Figure 2). Furthermore, the results showed that the number of very hot days in summer increased steadily (Figure 3). This is because the mean temperature will increase, and it appears that there is no big change about year-to-year variations of temperature (Figure 4). In addition, frequencies of torrential rains increased steadily (Figure 5). The season seems that the precipitation of each rainfall will increase steadily because of increase in water vapor in the air as well as increase in average rainfall (Note 2).


Contact:

Mr. Miura
Research Cooperation Section, Komaba branch office of Kashiwa-region
Center for Climate System Research, University of Tokyo
Tel: 03-5453-3953 Fax: 03-5453-3964 URL: http://www.ccsr.u-tokyo.ac.jp/

Mr. Tanabe
Planning/Public Relations Office
National Institute for Environmental Studies
Tel: 029-850-2303 Fax: 029-851-2854 URL: http://www.nies.go.jp/

Japan Agency for Marine-Earth Science and Technology

Ms. Ota
Frontier Research Center for Global Change
Tel:045-778-5687 Fax:045-778-5497 URL: http://www.jamstec.go.jp/frcgc/jp/
Mr. Gochou
Public Relations Division, Administration Department
Tel:046-867-9066 Fax: 046-867-9055 URL: http://www.jamstec.go.jp/



Note 1: There are many uncertainties about prediction on the absolute value of temperature rise. Considering all the results from the present models in the world together, it is said that if the concentration of carbon dioxide in the atmosphere is fixed to twice the present value, the temperature rise will range between 1.5 and 4.5°C. In this model, the temperature increased by 4.2°C.

Note 2: Since year-to-year natural fluctuations are quite large, the number of very hot days in summer and torrential rains won't always increase monotonously from year to year. In connection with this, generally it is difficult to link the unusual weather on a certain year (this year, for example) with global warming.