Dr. Syukuro Manabe, Who Demonstrated “Arctic Amplification,” Was Deservingly Awarded the Nobel Prize in Physics
Dr. Syukuro Manabe, who demonstrated “Arctic amplification,” was deservingly awarded the Nobel Prize in Physics
November 2021
Professor Emeritus, National Institute of Polar Research and the Graduate University for Advanced Studies
(atmospheric science / polar climatology)
Takashi Yamanouchi
The Nobel Prize in Physics was awarded to Professor Syukuro Manabe of Princeton University in the United States. I am very pleased to hear that a researcher in a subject related to mine has been awarded the Nobel Prize in Physics, and I’d like to highlight his contributions to polar research.
Dr. Manabe earned a Doctor of Science degree from the University of Tokyo’s graduate school (doctoral course) in 1958, where he studied meteorology at the Department of Geophysics in the Faculty of Science. Shigekata Shono, a well-known professor of meteorology who passed away young, was the advisor, and I only knew him as the author of the textbook of meteorology. Japan was still poor at the time, with few research resources, and the research environment did not apparently ideal back then. Many of the top meteorologists that time moved to the United States, where they pursued their vital studies around the world. I can easily name more than ten meteorologists just from the University of Tokyo besides Dr. Manabe, and from Tohoku University, Dr. Syun-Ichi Akasofu (Auroral physicist) and others who also moved out of Japan. I couldn’t even think of any other meteorologists left from that generation that remained in Japan. In one of his interviews, Dr. Manabe said that he chose the United States not just for its computer resources, but also for its environment, which allowed him to study without interference from human relations.
Let’s return to Dr. Manabe’s research. The first breakthrough came in 1967 (Manabe and Wetherald, 1967). The vertical distribution of temperature was calculated in a previous article (Manabe and Strickler, 1964) in a one-dimensional atmospheric model (reproducing atmospheric conditions with a computer) by the close interaction of radiative and convective heat transfer (radiative convective equilibrium). When the amount of water vapor (relative humidity) in the atmosphere is set to a fixed level, such as constant relative humidity, the results were successful in theoretically deriving the vertical temperature distribution and ground surface temperature in each latitude band, which were quite near to the state seen in the Earth atmosphere. This suggests that the model adequately explained the greenhouse effect of the Earth’s atmosphere.
Furthermore, this model indicates how the temperature distribution changes, when the atmospheric carbon dioxide(CO2) concentration, which causes the greenhouse effect, is modified. As the consequence, the troposphere and ground surface temperatures rises slightly while the stratosphere has a considerable temperature decline (Fig. 1). The average temperature on the ground surface increased by 2.36℃ when CO2 content was doubled from the average value of 300 ppm representative at the time to 600 ppm. This was epoch-making in science because it was the first model that accurately simulated the physical process by which anthropogenic CO2 emissions induced a rise in surface temperature.
According to the Intergovernmental Panel on Climate Change (IPCC) Sixth Assessment Report (IPCC, 2021) published in August, CO2 concentrations in 2100 AD would be nearly doubled (600 ppm) if emissions were not controlled very well, and the average temperature rise at the time was estimated to be 4 to 5 degrees Celsius, so even higher values are expected in the report. By the way, the greenhouse effect does not work the same in the stratosphere; the stratosphere’s heat balance is maintained by the heating caused by ozone’s absorption of solar radiation and the net cooling caused by CO2‘s emission. It cools as CO2 levels rise, increasing the emission of infrared radiation, and it was surprising that this conclusion was demonstrated later.
The next important breakthrough was the adoption of a three-dimensional general circulation model (GCM) (Manabe and Wetherald, 1975). It had previously been the result of averaging the entire world with a one-dimensional model, but, since the Earth has an atmosphere and the ocean flows, and the effect of heat and momentum transfer is significant. The general circulation model was utilized for the atmosphere, and the ocean was represented by a simple sea surface, and the cloud cover was fixed. The Earth is divided into grids of around 500 km scale, with 9 layers in the vertical direction to solve equations relating to physical quantities, and air movement (wind) and heat transport are set at time intervals. It was a simplified model that used a fixed ratio to represent the differences between continents and seas rather than the actual geographic distribution. The ice-albedo feedback, on the other hand, was taken into account, which stated that the area of snow and ice in the polar areas was affected by temperature. As a result, when CO2 was doubled, the average global temperature rose by 2.93 degrees Celsius. However, there was a significant difference in the troposphere depending on latitude, especially near the ground, with temperatures rising 2-3 times more in the high latitude zone than in the low and middle latitude regions. The sea ice shift was working. This is what is currently referred to as the “Polar amplification” of global warming.
The next model (Stouffer, Manabe, and Bryan, 1989) has progressed significantly and has evolved into a “Coupled model” that links atmospheric and ocean general circulation models. The geographical distribution had become nearly realistic, heat transport in the ocean had been expressed, clouds had been adjusted based on relative humidity (clouds emerge when relative humidity surpasses 99 percent), and CO2 concentration had increased at a rate of 1% per year (roughly equivalent to the actual increase; an equilibrium state at a fixed concentration was derived in previous models). This model became the prototype of the climate model that is now commonly used. The result shows that considerable warming is occurring in the Northern Hemisphere’s high latitudes, such as the Arctic, while warming in the Southern Hemisphere is moderate, particularly south of latitude 60° S. Because the sea area in the Southern Hemisphere is larger than in the Northern Hemisphere, thermal inertia is high and warming is difficult. Also, strong westerlies on the near surface induce the Ekman drift current, which drives the deep circulation, and these flows have the effect of limiting ocean warming in the Southern Hemisphere.
Dr. Manabe was the first to explain Arctic amplification (as defined by Serreze and Francis, 2006) and East-Antarctic warming suppression, or the north-south contrast of warming, which is significantly important to us, polar researchers. Before this study, there was a historical publication (quoted in Flohn, 1978) that discussed the asymmetry of the north-south climate based on observation results from the International Geophysical Year (IGY) 1957-58, however, the paper received little attention at the time. I only later became aware of this. Dr. Manabe and his group have successfully explained the north-south contrast due to the difference in energy balance shown as the observation results, by the three-dimensional atmospheric-ocean coupled model. He has clearly made a significant contribution to the Arctic and Antarctic atmospheric sciences and climatology. If you are interested, please refer to the recently published brief review paper (Manabe, 2019).
Dr. Manabe winning the Nobel Prize in Physics proved that geophysics, which is one of the classical physics applications, such as meteorology and climatology, is universally qualified for such an award. I took it as a message that the current global warming crisis facing the global environment really is a physics-based issue, and that we need to pay more attention to this tough situation and to put more effort to limit anthropogenic CO2 emissions. We shall hope that this is an opportunity to get rid of global warming skeptics and pool our resources to restrain global warming.
References
- Flohn, H., 1978. Comparison of Antarctic and Arctic climate and its relevance to climate evolution. Antarctic Glacial History and World Palaeoenvironments, CRC Press, London, 3-13.
- IPCC, 2021: Summary for Policymakers. In: Climate Change 2021: The Physical Science Basis. Contribution of Working Group I to the Sixth Assessment Report of the Intergovernmental Panel on Climate Change. Cambridge University Press.
- Manabe, S. and Strickler, R. F., 1964. Thermal equilibrium of the atmosphere with a convective adjustment. J. Atmos. Sci., 21, 361-385.
- Manabe, S. and Wetherald, R. T., 1967. Thermal equilibrium of the atmosphere with a given distribution of relative humidity. J. Atmos. Sci. 24, 241–259.
- Manabe, S. and Wetherald, R. T., 1975. The effect of doubling CO2 concentration on the climate of a general circulation model. J. Atmos. Sci. 32, 3–15.
- Manabe, S., 2019. Role of greenhouse gas in climate change. Tellus A, 71, 1620078, doi.org/10.1080/16000870.2019.1620078.
- Serreze, M. C. and Francis, J. A., 2006. The Arctic amplification debate. Clim. Change, 76, 241-264.
- Stouffer, R. J., Manabe, S. and Bryan, K., 1989. Interhemispheric asymmetry in climate response to a gradual increase of atmospheric CO2. Nature 342, 660–662.