Nobel Prize lecture: Syukuro Manabe, Nobel Prize in physics 2021

TL;DR

Earth’s atmosphere raises the global mean surface temperature by about 33 degrees centigrade because greenhouse gases absorb and emit long-wave radiation, preventing much of the surface’s upward energy flux from escaping directly to space. Increasing greenhouse gas concentrations raises the effective emission height, making it harder for radiation from lower atmospheric layers to reach the top of the atmosphere.

Transcript

nobel laureates in physics and chemistry laureates in economic sciences members of the academy ladies and gentlemen on behalf of the royal swedish academy of sciences i wish you all welcome to the 2021 nobel lectures in physics and chemistry and the lecture of this various ricks bank prize in economic sciences in memory of alfred nobel we are just ... Read More

Key Insights

• Earth’s atmosphere warms the global mean surface by about 33 degrees centigrade, based on the difference between the plus 14.7 degrees centigrade surface temperature and the approximately minus 18.6 degrees centigrade effective planetary emission temperature.
• Earth’s planetary energy balance is maintained between net incoming short-wave solar radiation and outgoing radiation at the top of the atmosphere. Satellite observations give the globally averaged outgoing radiation as 240 watts per square meter.
• The effective emission temperature is derived by treating the Earth-atmosphere system as a blackbody under the Stefan-Boltzmann law. The resulting value, minus 18.6 degrees centigrade, is substantially colder than Earth’s observed global mean surface temperature.
• The troposphere’s temperature decreases almost linearly with height, while the lower stratosphere is described as almost isothermal. This vertical structure helps explain why radiation escaping from an elevated atmospheric layer has a lower effective temperature than the surface.
• Kirchhoff’s law requires a substance’s absorptivity at a given wavelength to equal its emissivity. Earth’s surface behaves almost like a blackbody, so it absorbs most radiation reaching it and emits an upward long-wave flux in accordance with the same principle.
• Greenhouse gases are minor atmospheric constituents that collectively absorb a major fraction of the upward blackbody radiation emitted by Earth’s surface. The lecture identifies water vapor, carbon dioxide, nitrous oxide, and methane as important examples.
• The atmosphere traps heat because its absorption of upward radiation from the relatively warm surface is substantially larger than its emission from colder atmospheric layers. This process prevents much of the surface’s long-wave flux from reaching the top of the atmosphere directly.
• Increasing greenhouse gas concentrations increases the infrared opacity of the atmosphere. The effective center of outgoing radiation then shifts higher, making it harder for radiation emitted from lower atmospheric regions to reach the top of the atmosphere.

Questions & Answers

Q: What evidence demonstrates Earth’s atmospheric greenhouse effect?

Satellite observations show that the globally averaged outgoing radiation at the top of the atmosphere is 240 watts per square meter. Treating the Earth-atmosphere system as a blackbody gives an effective emission temperature of about minus 18.6 degrees centigrade. Because the global mean surface temperature is plus 14.7 degrees centigrade, the atmosphere keeps the surface about 33 degrees warmer.

Q: How does Earth maintain its planetary energy balance?

Earth’s planetary energy balance is maintained between net incoming short-wave solar radiation and outgoing radiation measured at the top of the atmosphere. The lecture reports a globally averaged outgoing flux of 240 watts per square meter from satellite observations. This observed flux provides the basis for estimating the planet’s effective emission temperature through the Stefan-Boltzmann law of blackbody radiation.

Q: Why is Earth’s surface warmer than its effective emission temperature?

Earth’s surface is warmer because the atmosphere absorbs and emits long-wave radiation. Greenhouse gases absorb a major fraction of the upward blackbody radiation emitted by the relatively warm surface, preventing it from escaping directly to the top of the atmosphere. This trapping produces a surface temperature about 33 degrees centigrade above the planet’s effective emission temperature.

Q: Which gases contribute to the atmospheric greenhouse effect?

The lecture identifies water vapor, carbon dioxide, nitrous oxide, and methane as greenhouse gases. Although these gases are minor constituents of the atmosphere, together they absorb a major fraction of the upward long-wave radiation emitted by Earth’s surface. Their absorption and emission affect how much energy reaches the top of the atmosphere and how warm the surface remains.

Q: How does Kirchhoff’s law explain atmospheric radiation?

Kirchhoff’s law states that, for a given wavelength, a substance’s absorptivity equals its emissivity, with emissivity defined relative to theoretical blackbody emission. Earth’s surface behaves almost as a blackbody, so it absorbs nearly all radiation reaching it and emits upward long-wave radiation. Atmospheric greenhouse gases likewise both absorb and emit radiation according to this relationship.

Q: Why does the upward long-wave radiation flux change with height?

The upward long-wave radiation flux changes as it passes through the atmosphere because greenhouse gases both absorb and emit radiation. Absorption depletes the flux originating from the relatively warm surface, while atmospheric emission adds radiation to it. The net flux therefore decreases or increases with height depending on whether depletion through absorption or acquisition through emission is greater.

Q: How do rising greenhouse gas concentrations warm the troposphere?

Rising concentrations of a greenhouse gas such as carbon dioxide increase the infrared opacity of the atmosphere. Radiation emitted from lower atmospheric regions then has greater difficulty reaching the top of the atmosphere. As opacity increases, the average height of the layer from which outgoing radiation originates moves upward, linking increased greenhouse gas concentration to warming at the surface and in the troposphere.

Q: What was Syukuro Manabe recognized for by the 2021 Nobel Prize?

Syukuro Manabe shared half of the 2021 Nobel Prize in Physics with Klaus Hasselmann for the physical modeling of Earth’s climate, quantifying variability, and reliably predicting global warming. Manabe and his collaborators developed advanced models of the greenhouse effect and general circulation models that are essential for weather predictions. His Nobel lecture focused on greenhouse gases and climate change.

Summary

This video features the Nobel lectures in Physics and Chemistry, as well as the lecture for the Sveriges Riksbank Prize in Economic Sciences, in memory of Alfred Nobel. Due to the COVID-19 pandemic, the format of the lectures deviates from the traditional in-person event in Stockholm, with the laureates delivering their lectures from different parts of the world. The video emphasizes the importance of research as an international endeavor and highlights the significant scientific breakthroughs made, particularly in the development of vaccines and the understanding of complex systems like climate change and molecular synthesis.

Questions & Answers

Q: What are the primary challenges in understanding complex systems in nature and society?

Complexity is the rule, not the exception, in physics. While early physics focused on simple systems, further progress requires a direct assault on complex systems. In nature, understanding the coupled systems that determine Earth's climate is crucial. Additionally, understanding the complex behavior of glassy materials is essential, as it has implications for various fields beyond physics.

Q: Who are the Nobel laureates in physics for their contributions to our understanding of complex systems?

The Nobel Prize in Physics is divided into two parts, both related to complex systems. The first part is awarded jointly to Dr. Shruki Manabe of Princeton University and Professor Claus Hasselman of the Max Planck Institute for Meteorology. They are recognized for their work on modeling and predicting Earth's climate variability and global warming.

Q: What is the greenhouse effect and its implications for Earth's climate?

The greenhouse effect refers to the role of greenhouse gases in trapping heat and increasing Earth's surface temperature. The atmosphere, acting as a greenhouse, absorbs and emits long-wave radiation, preventing it from escaping into space. The increase in greenhouse gas concentration, such as carbon dioxide, leads to higher temperatures at Earth's surface and in the troposphere. This phenomenon, known as global warming, has significant implications for the climate system.

Q: How does water vapor contribute to the greenhouse effect and global warming?

Water vapor is a potent greenhouse gas that strongly absorbs and emits long-wave radiation. As greenhouse gas concentrations increase, the temperature in the troposphere and at Earth's surface rises. One important factor amplifying global warming is the positive feedback process involving water vapor. The increased temperature leads to increased humidity and, consequently, a higher greenhouse effect, further enhancing global warming.

Q: How has modeling contributed to our understanding of climate change?

Early models, such as the one-dimensional radiative convective model, provided insights into temperature changes at the Earth's surface and in the atmosphere in response to increasing greenhouse gas concentrations. These models demonstrated the amplifying effect of water vapor feedback on global warming. Later, three-dimensional general circulation models, coupled with atmosphere-ocean models, allowed for more comprehensive simulations of the climate system, providing valuable data for climate predictions and assessments.

Q: What are the implications of global warming on the Earth's water cycle?

Global warming affects not only the global mean rates of precipitation and evaporation but also their geographical distribution. As temperature increases, the rate of evaporation and the transport of water vapor by large-scale circulation in the atmosphere also increase. Consequently, while precipitation may increase in some water-rich regions, it may decrease in water-poor regions, resulting in changes to water availability, river discharge, and soil moisture distribution.

Q: How do the Nobel laureates' contributions in chemistry impact society?

The laureates in chemistry have discovered and developed novel methods for synthesizing molecules. Their work has allowed for increased precision and has found applications in various areas, benefiting society in multiple ways. Their contributions also highlight the importance of research in advancing understanding and making informed policy decisions.

Q: Why is research an international endeavor?

Research knows no boundaries and is a collective effort to advance knowledge and solve global challenges. The COVID-19 pandemic has further highlighted the importance of international collaboration in scientific breakthroughs, such as the development of vaccines. Research allows for a deeper understanding of complex phenomena and helps inform policy decisions to combat pandemics and achieve sustainable development.

Q: What is the significance of Alfred Nobel's testament in relation to the Nobel Prizes?

Alfred Nobel's testament emphasizes that the Nobel Prizes should be awarded without consideration of nationality and to the worthiest individuals. The past two years have made it clear that research is indeed an international endeavor, with scientific breakthroughs and progress being achieved by researchers from various countries. This further reinforces the importance of recognizing excellence and promoting collaboration in scientific endeavors.

Q: How does misinformation and anecdotal data affect scientific progress?

Statistics and mathematics play crucial roles in analyzing large data sets and understanding complex matters. Sadly, some people still use anecdotal data to question the efficacy of scientific developments, such as vaccines. This misinformation can be unintentionally or intentionally propagated, leading to devastating consequences in terms of human lives and suffering. It is essential to rely on rigorous scientific analysis and objective data to make informed decisions.

Q: What is the significance of the continuous progress of science and research?

Sir Isaac Newton's quote, "If I have seen further, it is by standing on the shoulders of giants", highlights the cumulative nature of scientific progress. The constant advancement of science and research builds upon the work of previous generations and enables present and future researchers to explore new frontiers. Each generation of giants in research paves the way for future breakthroughs, leading to deeper understanding, new knowledge, and improved societies.

Takeaways

The Nobel lectures emphasize that research is an international endeavor, essential for understanding complex systems and making informed policy decisions. Scientific breakthroughs, such as the rapid development of COVID-19 vaccines, highlight the importance of rigorous analysis and objective use of data. The laureates' contributions in physics, chemistry, and economics have provided deeper knowledge, improved precision, and offered new insights and applications. The progress of science and research relies on building upon previous knowledge and serves as a foundation for even greater advancements in the future.

Summary & Key Takeaways

• Earth’s energy balance is maintained between net incoming short-wave solar radiation and outgoing radiation at the top of the atmosphere. Satellite observations place globally averaged outgoing radiation at 240 watts per square meter. Blackbody calculations give an effective planetary emission temperature of minus 18.6 degrees centigrade, far below the surface average.

• The global mean surface temperature is plus 14.7 degrees centigrade, about 33 degrees warmer than the effective emission temperature. This difference demonstrates the atmosphere’s greenhouse effect. The troposphere generally cools with height, while the lower stratosphere is described as almost isothermal, placing the effective emission center within the colder atmosphere.

• Greenhouse gases, including water vapor, carbon dioxide, nitrous oxide, and methane, absorb much of the long-wave radiation emitted by Earth’s surface. As their concentrations rise, atmospheric infrared opacity increases and the effective emission height moves upward. Radiation from lower atmospheric layers consequently has greater difficulty escaping to the top of the atmosphere.