Background Image

Teaching Notes

In this Section

Teaching Notes

Grade Level

High school, but could be adapted to 8th grade.

Learning Goals

After completing this unit, users will be able to:

  • Identify the important wavelength spectrums associated with solar and terrestrial radiation
  • Associate temperatures of objects with their electromagnetic emission wavelengths
  • Recognize that different gases interact with radiation of different wavelengths differently
  • Relate greenhouse gas concentrations to temperature
  • Communicate their findings orally using appropriate climate change and Earth science vocabulary.

Rationale

This unit helps students understand the basics of the greenhouse effect and the relationship between greenhouse gas concentrations and global temperatures.  Students will be able to understand terminology related to solar and terrestrial radiation.  Students will be able to recognize different greenhouse gases and the mechanism by which they interaction with terrestrial radiation.  

Students will use a variety of web based visualization tools and Excel to plot data obtained from these tools.

Key Concepts and Vocabulary

Black body: A finite-sized body that absorbs all incident electromagnetic radiation.

Electromagnetic (EM) radiation: Electromagnetic radiation is produced as a result of conversion of a body’s internal thermal energy to electromagnetic energy – i.e., energy associated with the motion of charged particles.  EM radiation behaves both like a stream of massless particles and waves as it is transmitted through a medium.

Shortwave radiation: Usually refers to the electromagnetic radiation in near- visible and visible wavelengths (0.3 - 4 mm),– i.e., wavelengths where most of Sun’s energy is concentrated.

Longwave radiation: Usually refers to the electromagnetic radiation in infrared and near-infrared wavelengths (longer than 4 mm) – i.e., wavelengths where most of Earth’s radiative energy is concentrated.

Anthropogenic emissions:  Emissions resulting from human activities.

Greenhouse gas (GHG): A gas that absorbs energy in wavelengths corresponding to long-wave radiation.

Greenhouse effect: The process of energy absorption and re-radiation by the GHGs in the atmosphere.

Background Information

To understand the role of greenhouse gases in global climate change, it is important to understand the basics of blackbody radiation and the interaction of greenhouse gases with Earth’s long-wave radiation.  An introductory PowerPoint presentation on this topic is available here.

All bodies emit energy in the form of electromagnetic (EM) radiation.  The sun’s energy reaches Earth in the form of light – a form of EM radiation (Figure 1). We feel the warmth from a fireplace even with a glass barrier because of EM radiation. The warm coil on the stove glows because it emits EM radiation and the coil’s heat is felt at a distance because of EM radiation.  Heat and light are both forms of electromagnetic radiation.  Other forms of electromagnetic radiation include: x-rays, gamma-rays, and radio waves.  The different forms of EM radiation correspond to different energies and wavelength ranges as illustrated in Figure 1.

EM Wavelength Spectrum

A black body is a body that absorbs all radiation that it receives and emits radiation in all wavelengths.  The net intensity of the radiation emitted by a blackbody is dependent on its temperature (intensity is proportional to T4), with hotter bodies emitting greater amounts of radiation.  While blackbodies emit radiation over all wavelengths, a significant fraction of their emitted energy is concentrated in a limited range of wavelengths.  The wavelength corresponding to the peak intensity of emission decreases with increasing temperature. 

Incoming Sunlight vs. Outgoing Heat

Sun and Earth can both be considered black bodies in analyzing their radiative properties.  The EM radiation from Sun is primarily in short or visible wavelengths (0.4 – 0.7 mm) corresponding to the Sun’s high temperature (~ 5777 K), while the EM radiation associated with Earth’s emission to space is primarily in the infrared wavelength range (1-10 mm), corresponding to its cooler temperature (~ 298 K; Figure 3).  As Earth’s temperature is largely in equilibrium, the incoming short-wave radiation should be balanced by the outdoing long-wave radiation.

Not all the long-wave radiation emitted by Earth escapes to space.  Some gases in the atmosphere can absorb Earth’s long-wave radiation and heat up the surrounding air by collisions with the neighboring molecules.  The heated layer can then radiate energy back to Earth’s surface.  This effect of trapping the outgoing long-wave radiation and warming up Earth’s atmosphere and surface is referred to as the Greenhouse effect and the gases that absorb long-wave radiation and create the greenhouse effect are called Greenhouse gases (GHGs).

EM Radiation Spectrum of Sun and Earth

Without GHGs, Earth’s temperature would be too cold for humans (~ 0oF rather than 60oF that we have currently).  Thus, GHGs are essentially for maintaining life on Earth.  The most abundant GHG in the atmosphere is water vapor.  The concentration of water vapor in the atmosphere is a consequence of Earth’s temperature, existing in equilibrium with liquid water and ice on Earth’s surface.  The atmospheric water vapor concentration is not directly controlled by anthropogenic emissions.  

The Greenhouse Effect

Some of the important greenhouse gases with anthropogenic sources are: Carbon dioxide (CO2), Methane, (CH4) and Nitrous Oxide (N2O).  The concentrations of these gases can critically control the extent of Earth’s long-wave radiation trapped in the atmosphere.  Anthropogenic sources of these gases are primarily from the combustion of fossil fuels.  The concentrations of greenhouse gases have steadily increased since the Industrial Revolution.  A corresponding increase in the average global temperatures has also been observed.

Key References:

General Meteorology applets: http://people.cas.sc.edu/carbone/modules/mods4car/index.html

EPA’s Climate change site: http://epa.gov/climatechange/index.html

NASA’s climate change site: http://climate.nasa.gov/

NASA greenhouse effect: http://earthobservatory.nasa.gov/Experiments/PlanetEarthScience/GlobalWarming/GW_Movie3.php

US greenhouse gas inventory: http://www.epa.gov/climatechange/emissions/usinventoryreport.html

Global greenhouse data: http://www.epa.gov/climatechange/emissions/globalghg.html

Greenhouse effect (NCAR): http://www.ucar.edu/learn/1_3_1.htm

Greenhouse gas concentrations: http://cdiac.ornl.gov/pns/current_ghg.html

Learn about Infrared: http://coolcosmos.ipac.caltech.edu/cosmic_kids/learn_ir/index.html  

 

 

Instructional Strategies

General Approach

This unit has multiple parts that are best done with students in pairs or groups of 3.  The grouping will allow students to support each other and discuss their findings as they explore the different tools.  Students will use the visualization tools to determine the wavelengths associated with different electromagnetic waves and determine the primary emission wavelengths for Sun and Earth and understand the role of greenhouse gases in trapping long-wave radiation and relation between global GHG concentrations and global temperature.

The outcomes of these activities are: 

1) Gaining a familiarity of electromagnetic (EM) radiation by blackbodies

2) Understanding EM emission characteristics as a function of blackbody body temperature

3) Knowledge of EM radiation interaction with different gas molecules and recognition of greenhouse gases (GHGs)

4) Role of GHG concentrations in controlling Earth’s atmospheric temperature.

Flow of activities throughout this project.

Implementation

Anticipatory Set – Assuming students have already been introduced to the general climate change vocabulary (e.g., GHGs, GHG emissions, Carbon footprint), begin the unit by having students explore what Earth’s source of energy is and how it is received.  What differences in temperatures have the students noticed between cloudy and clear nights in winter?  Once the students understand that Sun is the source of energy and that “heat” from Earth can escape to space, proceed to unit. 

General Procedure

  1. Using the Electromagnetic spectrum applet determine the wavelengths ranges associated with UV, visible, infrared, and microwave spectra. The students should be allowed to explore the applet and familiarize themselves with the different terminologies of the EM wavelength spectrum.  In particular, it is important to recognize the range of visible and near-visible wavelengths (UV, near-infrared), and the wavelengths associated with heat transmission (infrared, microwave).
  2. Using the blackbody spectrum applet, students should be able to determine the primary wavelengths corresponding to Sun’s and Earth’s EM radiation.  The students should explore the applet and develop an understanding of the relationship between the temperature of a blackbody and its peak emission wavelength.
  3. a. Use the applet illustrating the wavelength-dependent interaction between different chemical compounds and electromagnetic radiation to determine what makes a gas a greenhouse gas. Students should explore the applet, choosing different EM radiation types (UV, visible, infrared, or microwave) and selecting different molecules, to determine for themselves that some molecules may interact with EM radiation emitted from Earth, i.e., act as greenhouse gases. (This is more appropriate to 8th or 9th graders).

    OR

    b. With the aid of a more advanced applet (Click on the link and then on the picture under “Collisional Heating by CO2 in the Atmosphere”), students can explore in detail the absorption characteristics of different gases in the infrared wavelength regime.  They can study the differences between different greenhouses gases with respect to their interaction with Earth’s emission spectrum.  (This is more appropriate to high school students).

  4. The applet on greenhouse effect helps students make the connection between greenhouse gases and Earth’s temperature.  In this applet, interaction of an ideal atmosphere with incoming solar radiation and outgoing terrestrial radiation is considered.  Students can vary the concentration of greenhouse gases in the atmosphere and determine the resultant average temperature of the modeled atmosphere.  On completion of this unit, students should be able to explain the role of GHGs in regulating Earth’s temperature and the consequence of higher GHG concentrations on Earth’s future temperature.

Closure – By the end of the unit, the students should recognize the importance of the role of GHGs in keeping Earth warm enough for humans to survive and understand that the greenhouse effect is the result of absorption of long-wave radiation from Earth’s surface by some atmospheric gases. The students should also be able to list a few major greenhouse gases.  

Learning Concepts

This module  lend itself to  upper level science courses. In  Physics , wave lengths and  the concept of electromagnetic radiation may be discussed in greater detail.  It would also be appropriate to incorporate these activities with a chemistry lecture related to chemical bonds, photochemical reactions, etc. Data graphing and graph interpretation could all be integrated into mathematics class as a real-world application of technology skills. 

Science Standards

The following New York State, Mathematics, Science and Technology (MST) Standards are supported by this unit: (http://www.p12.nysed.gov/ciai/standards.html )

STANDARD – Analysis, Inquiry, and Design

Students will use mathematical analysis, scientific inquiry, and engineering designs, as appropriate, to pose questions, seek answers, and develop solutions.

  • Abstraction and symbolic representation are used to communicate mathematically.

STANDARD 4 - The Physical Setting

Students will understand and apply scientific concepts, principles, and theories pertaining to the physical setting and living environment and recognize the historical development of ideas in science.

  • Matter is made up of particles whose properties determine the observable characteristics of matter and its reactivity
  • Energy exists in many forms, and when these forms change, energy is conserved
  • Energy and matter interact through forces that result in changes in motion.

STANDARD 6—Interconnectedness: Common Themes

Students will understand the relationships and common themes that connect mathematics, science, and technology and apply the themes to these and other areas of learning.

  • Models are simplified representations of objects, structures, or systems used in analysis, explanation, interpretation, or design.
  • Equilibrium is a state of stability due either to a lack of change (static equilibrium) or a balance between opposing forces (dynamic equilibrium).
  • Identifying patterns of change is necessary for making predictions about future behavior and conditions

Assessment

Assessment should be based on quizzes/homeworks/exams.

Other Resources and Files