Interview - The Earth Simulator and Its Contributions to Global Warming Projection Research

First off was the launch of the "Project for Sustainable Coexistence of Human, Nature, and the Earth" in 2002 by the Ministry of Education, Culture, Sports, Science and Technology (MEXT). This project sought scientific research findings on global environmental issues, such as global warming and extreme weather events with serious impacts on human life and industry, to facilitate responding policy measures. One of the major research missions was focused on global warming projection. Garnering the expertise of universities, government institutions, and industries, including the FRCGC and Tokyo University, this projection aimed to contribute to the IPCC Fourth Assessment Report. In the same year, the Earth Simulator had just begun operations, and we were able to use it effectively. The Earth Simulator was, at the time of its debut, a super computer with the fastest computing ability-40 teraflops (trillion calculations per second)-in the world.

Main research achievements

The first achievement is the successful development of a climate model that has the world's highest resolution. In climate projection research, we resolve the atmosphere and the ocean by grid mesh systems. We then apply physical laws and necessary conditions to these systems to calculate future changes in climate variables, such as temperature. There are several models developed for projection research in Japan. Among them, a coupled atmosphere-ocean model with a resolution of 100x100 sq km for the atmosphere was developed, enabled by the Earth Simulator. Other coupled atmosphere-ocean models existing in the world normally have 300x300 sq km resolutions for the atmosphere. With our highest resolution coupled model, we obtained advanced achievements in the projection and attribution of global warming.
We also made great strides in our understanding of the impact of global warming on extreme events. In this case, we developed an atmosphere model with a super-high resolution of 20x20 sq km that could resolve the essential details of the structures of tropical cyclones, such as typhoons and hurricanes. Simulation experiments of tropical cyclones in the present climate were reasonably consistent with actual observations in terms of their genesis areas and storm tracks in the world. We applied this model to the climate projected for the next 100 years and found that the strength of typhoons and hurricanes will increase.
In addition, to develop a new model that more closely reflects actual conditions on Earth and thereby gain even deeper insight, we incorporated the concept of a carbon cycle* into a conventional climate model. According to a conventional model, an increase in CO2 would cause global warming without any feedback. However, the newly developed model shows that global warming due to the increase of CO2 affects plants and organic substances and causes feedback resulting in further acceleration in global warming.

These projection research outcomes were then reflected in the IPCC Fourth Assessment Report. Thanks to the emergence of the Earth Simulator, the outcomes embodied in this Report have shown a far higher level of results in terms of resolution and precision than those in the Third Assessment Report. As a result, the Fourth Assessment Report has received wide acclaim. The IPCC chairman has also expressed his great appreciation for the researchers working on the Earth Simulator.