1-12: Global Energy Balance

Pre-Class Preparation

• To understand the processes and pathways of energy transformation from solar radiation coming into the earth system to infrared radiation returning to outer space.
• To understand the significance of greenhouse gases in establishing the natural energy balance of the earth system and how changes in greenhouse gases change heating and cooling rates.

Procedure

1. Read the learning unit.

   Class images

2. Take the learning unit quiz. Quizzes are available from your portfolio. You may access your portfolio via the list of students participating in this years course, as represented by the icon below.
   
   
3. Additional Required Reading. Although you are not ultimately responsible for content listed in this section, we encourage you to fully explore the links in order to provide a better scope on the upcoming class discussion.

   	Cool It!
   	Radiation, Climate and Climate Change. (From UNEP.)
   	The Role of Greenhouse Gases. (From UNEP.)

Class Discussion

• Problem to ponder...
  Planet earth emits the exact same amount of energy back to outer space that it receives from the sun. Then how can the surface of the planet warm up without upsetting this energy balance?

• Class Discussion Summary: by classmates Lea Bonebrake and Eric Thorberg

  We started out the lecture by continuing to discuss how solar energy is transformed into heat energy within the earth´s atmosphere, noting that 30% of the solar energy is reflected by clouds without being transformed into heat. We next studied the table of albedos. In the winter, the albedo tends to be higher and the absorbtion is lower; while in the summer, the albedo is lower and the absorbtion is higher. This has to do with the angle that the sun is hitting certain portions of the earth at different times. The discussion next moved to landscape reflectivity. The snow covered regions and the desert regions showed the highest reflectivity values, while certain forested regions showed higher absorption values. This demonstrates that deforestaion and conversion of lands to agricultural crops can increase the reflectivity of the landscape. The discussion finally turned to the reflectivities of carbon dioxide as opposed to other greenhouse gasses. Methane is shown to be 21 times more effective as a greenhouse gas than carbon dioxide, while nitrous oxide is 206 times more effective, and CFC´s can be up to 12400 times more effective. The natural changes in the input of solar radiation may be a cause of global temperature fluctuation, but the human influence on the atmosphere has a far greater effect. The lecture ended with the discussion that sulfates, while they counteract the heating effects of greenhouse gasses, they tend to be more localized and shortlived in the atmosphere.

  -- Lea Bonebrake
  

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  This lecture dealt with the global energy balance. This balance ties in closely with the previous lecture, the global hydrological cycle. Both of these systems, hydrological and energy, are intertwined. The lecture proceeded to look at the radiation balance on the earth. We took time to compare the different albedos of various surfaces. Snow has a significant change in reflectivity depending on its age, due to the process of sublimation. Deforestation has an affect on the overall reflectivity. Crops have a higher albedo than the forests (table 4); this results in a brighter surface of the earth. Two important changes were noted for the equations on radiative forcing. These refer just to the equations. for methane and nitrous oxide: the variables M, M_o, N, and N_o need to be under a square root sign. The lecture ended with the discussion of the effects of radiative forcing increases throughout the world. The comparison between the increase in radiative forcing of the greenhouse gases and forcing dealing with natural factors was examined. It was shown that radiative forcing has increased by 2 W m^-2 since the industrial revolution due to greenhouse gases. However, there exists a localized counter to this in the form of sulfates. The affect is localized due to the sulfates easily precipitating out of the atmosphere.

  -- Eric Thorberg

Post-Class Activities

• Participate in the electronic dialog. Use this forum for:
  • continuing class discussion;
  • posing new questions to students or the instructor;
  • responding to issues/questions raised by students in class/electronic dialog.

  Visitor Access (Visitors are welcome to participate in the dialog. Just click on the icon below)	Student Access (Students must post all dialog from their portfolio. Click on the icon below to access the student list.)

• Recommended Reading Materials

  	CoVis Greenhouse Effect Visualizer allows you to inspect scientific visualizations of the earth's climate.
  	Glossary of Climate Change Terms.
  	The Warm Earth- Thermal Remote Sensing (From the Applied Information Sciences Branch, NASA)
  	Lean, Judith, and David Rind, 1996: The Sun and Climate. Consequences, 2(1), 26-36.
  	Boucher, O. 1994: The Sulfate-CCN-Cloud Albedo Effect. Tellus, 47B, 281-287.
  	Charlson, R. J., et al. 1987: Oceanic Phytoplankton, Atmospheric Sulfur, Cloud Albedo and Climate. Nature, 326, 655-661.
  	Chuang, C. C., et al. 1994: Effects of Anthropogenic Sulfate on Cloud Drop Nucleation and Optical Properties. Tellus, 47B, 566-577.
  	Erickson, David J., et al., 1995: Climate Response to Indirect Anthropogenic Sulfate Forcing. Geophysical Research Letters, 22(15), 2017-2020.
  	Houghton, J.T., G.J. Jenkins, J.J. Ephraums, eds, 1990: 1990 Intergovernment Panel on Climate Change, Cambridge University Press, 45-61.
  	Houghton, J. T., L. G. Meira Filho, B. A. Callander N. Harris, A. Kattenberg, and K. Maskell, 1996: Climate Change 1995. The Science of Climate Change. Cambridge University Press, 58, 90-96.
  	Kiehl, J. T., et al. 1993: The Relative roles of Sulfate Aerosols and Greenhouse Gases in Climate Forcing. Science, 260, 311-314.

• References

  List of References