Prof. Syukuro Manabe and Climate Research

Yukio Masumoto

He is like a child full of curiosity. With all due respect to Prof. Manabe as a senior leader of our research field, this is the impression I had when I first met him, having known him only through his papers for a long time. I am sure many people will agree with me. However, it is impossible to avoid Prof. Manabe's papers when we try to study how the Earth's climate condition, under a coupled atmosphere-ocean-land system, is determined and how it changes in the past, present, and future. He is such a giant in this research field.

Prof. Syukuro Manabe was born in 1931 in Shinritsu Village (now Shikokuchuo City), Uma County, Ehime Prefecture, Japan. After completing his education at the old Mishima Junior High School (now Ehime Prefectural Mishima High School), he graduated from the Department of Geophysics, Faculty of Science, the University of Tokyo in 1953. He then went on to graduate school and received a Doctor of Science (geophysics) from the University of Tokyo in 1958. In the same year, he left for the United States to start his career as a research meteorologist at the US Weather Bureau. In 1963, he became a senior research meteorologist at the Geophysical Fluid Dynamics Laboratory, the National Oceanic and Atmospheric Administration. In 1968, he concurrently became a lecturer with the rank of professor at the Program in Atmospheric and Oceanic Sciences, Princeton University. In 1997, he was appointed as the Director of the Global Warming Research Program of the Frontier Research Center for Global Change, a joint project of the National Space Development Agency of Japan (NASDA) and the Japan Marine Science and Technology Center (JAMSTEC). In 2002, he returned to the Atmospheric and Oceanic Research Program at Princeton University, where he is currently a senior meteorologist (Fig. 14).

Fig. 14. Prof. Syukuro Manabe in 1997 at Princeton University (Photo by Princeton University, Office of Communications, Robert P. Matthews)

Prof. Manabe has devised a physical model of one-dimensional atmosphere, which is known as the radiative-convective equilibrium model^[1]. He also implemented this key process into a numerical model to determine the vertical temperature distribution in the atmosphere caused by the input of solar radiation energy to the Earth's atmosphere. Prof. Manabe was the first to quantify the role of radiatively active gases, such as water vapor, carbon dioxide, and ozone, as well as clouds, in reproducing the vertical temperature structure of the atmosphere^[2][3]. He even estimated with this model that the temperature of the Earth's surface would increase by about 2 °C under a condition of doubling the concentration of carbon dioxide, with other parameters fixed, due to the well-known "greenhouse effect"^[3]. These fundamental studies in his early career were the forerunners of the currently active research to clarify the relationship between the anthropogenic increase of greenhouse gases and global warming. The importance of these studies is highly recognized in the scientific background on the Nobel Prize in Physics in 2021^[4] (Fig. 15).

Fig. 15. Prof. Manabe, with Dr. Kirk Bryan (left) and the founder and former director of Geophysical Fluid Dynamics Laboratory, Joseph Smagorinksy (right). (Photo courtesy of the Geophysical Fluid Dynamics Laboratory)

Prof. Manabe, thereafter, developed an atmospheric general circulation model with this radiative-convective process, which could reproduce three-dimensional circulations of the atmosphere, and again obtained the result that an increase in the concentration of atmospheric carbon dioxide causes an increase in average surface temperature. In 1969, he and Dr. Kirk Bryan succeeded in capturing the three-dimensional basic structure of the Earth's climate system by combining an atmospheric general circulation model with an ocean general circulation model^[5][6]. In addition, using the world's first coupled model of atmosphere, ocean, and land surface processes thus developed, Prof. Manabe conducted the first study to clarify in detail how global climate changes when carbon dioxide is artificially increased^[7]. Since then, he has been continuing to advance coupled atmosphere-ocean-land surface models and has pioneered a new research field using the coupled models to understand processes and their mechanisms of Earth's climate variations and changes^{[8][9][10][11]}. His continuous efforts have led to many pioneering and important findings, including that global warming signatures appear faster in the Northern Hemisphere than in the Southern Hemisphere and that the oceans have a moderating effect on global warming conditions^[9]. These studies have made a significant contribution to our understanding of the physics of climate systems and formed the basis of the global warming simulations that are now widely used in discussions in the Intergovernmental Panel on Climate Change (IPCC) reports^[12].

Looking back on his research and achievements to date, we recognize that he has kept his style of thinking and modeling processes as simple as possible while preserving the essences of complex phenomena. This is exactly what physics is all about. Even with results from a complex coupled model, he always tries to explore mechanisms responsible for the processes and explain them in concise and clear ways. I cannot help but be amazed at the fact that he continues to have a keen eye to clarify the essence of climate systems and is still actively conducting research^[13]. It is fortunate for us that his interests as a scientist pointed to the Earth's climate system of ultra-complexity. The period from the late 1950s to the 1960s, when Prof. Manabe began his research, was also a time of great progress in the development of numerical models of the atmosphere and oceans and in the advancement of numerical methods. This development of the numerical models and Prof. Manabe's curiosity and sense of physics overlapped at the right time.

The issue of global warming is often treated as an environmental problem from the exit viewpoint because of its immense impact on various socioeconomic activities, including our daily lives. However, the Nobel Prize in Physics to Prof. Manabe this time can be taken as an important message that physics is the foundation for understanding and predicting global warming and global climate change. His research has deepened our understanding on the complex Earth's climate system, but the climate system itself exists still beyond our understanding, calmly taking anthropogenic activities. As the conditions surrounding the Earth's climate are changing, we need to further investigate, based on Prof. Manabe's research, how various phenomena in the atmosphere and oceans are affected under the global warming stress and how they interact with each other to modify the climate.

References

[1] S. Manabe and F. Möller, Mon. Wea. Rev. 89. 503 (1961).
[2] S. Manabe and R. F. Strickler, J. Atmos. Sci. 21. 361 (1964).
[3] S. Manabe and R. T. Wetherald, J. Atmos. Sci. 24. 241 (1967).
[4] The Nobel Committee for Physics, https://www.nobelprize.org/uploads/2021/10/sciback_fy_en_21.pdf (2021).
[5] S. Manabe and K. Bryan, J. Atmos. Sci. 26. 786 (1969).
[6] S. Manabe, Mon. Wea. Rev. 97. 775 (1969).
[7] S. Manabe and R. T. Wetherald, J. Atmos. Sci. 32. 3 (1975).
[8] K. Bryan, F. G. Komro, S. Manabe and M. J. Spelman, Science 215. 56 (1982).
[9] R. J. Stouffer, S. Manabe and K. Bryan, Nature 342. 660 (1989).
[10] S. Manabe, R. J. Stouffer, M. J. Spelman and K. Bryan, J. Clim. 4. 785 (1991).
[11] S. Manabe, M. J. Spelman and R. J. Stouffer, J. Clim. 5. 105 (1992).
[12] Intergovernmental Panel on Climate Change,
https://www.ipcc.ch/report/ar6/wg1/downloads/report/IPCC_AR6_WGI_Full_Report.pdf (2021).
[13] R. J. Stouffer and S. Manabe, Nature Clim. Change 7. 163 (2017).