# The Earth's Energy Budget

This lesson plan was developed by NSTA master teacher Jerry D. Roth through NSTA's partnership with NOAA.

Subject Area: - Primarily Geoscience, but the lesson can also be used for General Science that has an Earth Science component.

Standards Alignment-National Science Education Standards:

• Earth Science
• Structure of the Earth system
• Temperature differences in the atmosphere are a result of the way solar energy is absorbed as it moves through the atmosphere.
• Earth Science
• Structure of the Earth system
• Heat energy is transferred through the atmosphere by conduction and convection.

Time Required:

One class period will be needed to demonstrate the three types of heat transfer and the processes that light as radiation can undergo: reflection, absorption, and refraction. The actual tutorial will take two periods.

Overall Lesson Goal:

The student should come away from this lesson with an understanding of the Earth’s energy budget; the flow of energy from the sun to the Earth, and the outward flow from the Earth.

Individual Learning Objectives:

Understand that energy flows from the sun to the Earth as radiation. About 30% of the solar radiation that strikes the atmosphere is reflected or scattered. Roughly 20% of the solar radiation is absorbed by the atmosphere. The remaining radiation, approximately 50% is absorbed by the surface of the Earth.

Prerequisite Knowledge; Misconceptions/Preconceptions:

The total amount of radiation striking the Earth is equal to the total amount being radiated back into space. If more incoming radiation was absorbed, the Earth would get hotter. If more radiation was radiated back into space, the Earth would get cooler.

Ultimately, the sun is the source of all of our weather as it provides energy to drive other systems. Students understand that the sun makes them hot in the summer even though they may not understand the mechanism completely. Few really understand solar radiation or the lack of it is also what makes them cold in the winter.

The Earth rotates. This rotation puts one half of the Earth’s surface in line for sunlight to strike it. The other half of the Earth is radiating radiation back into space.

The three ways to move heat are radiation, which can take place through a vacuum; conduction, which requires the direct contact of materials; and convection, which causes a heated material to flow as it is being replaced by a cooler material. Three preparatory activities addressing heat transfer, radiation, conduction, and convection, can be found at the University Corporation for Atmospheric Research’s Web site Introduction to the Atmosphere. The activities are lower than recommended grade level and you may find they are too low for your students, but I’ve never had a group of students keep quiet when I pour carbon dioxide gas over a candle and extinguish it.

Once the students are comfortable with the types of heat transfer, they should move on to what may happen with radiation. Radiation can be reflected, refracted, or have its speed changed, or absorbed. All three of these happen in the atmosphere. Reflection occurs when radiation strikes an object and it bounces off. This happens in the atmosphere and on the surface of the Earth. Refraction, the changing of the speed of radiation as it energizes a substance it has entered is classically observed in rainbows, so we know it occurs in water molecules. Absorption is when the energy in the incoming radiation is passed from the electrons in the substance along to the nucleus of the atoms where it may be radiated back at a different wavelength, usually a lower frequency, longer wavelength wave. Reflection, refraction, and absorption are well explained at How Light Works.

We’ve got heat energy, electromagnetic radiation and the spinning Earth working together to produce weather and climate. What happens to solar radiation when it comes to the Earth’s atmosphere is covered by the Solar Radiation Learning Module from the College of Alameda’s Physical Geography Department. Access the learning module with your students and allow them to follow along as you lead them. Demonstrate how to navigate the site then allow them to go on their own. This module helps students understand the interaction of all of the factors above.

Procedures/Instructional Strategy:

All of the aspects of heat transfer and light processes can be demonstrated quickly and easily in one period. You need to set up everything in advance and turn on the heat sources as the students walk into class.

Step 1

• (a): Place a 1000mL beaker filled with 800 mL water on a hot plate and turn the hot plate on hot to heat the liquid. Place another beaker with the 800 mL of water on another hot plate but do not turn this hot plate on.
• (b): I would set up and turn on a heat lamp of 250 watts. Be sure to warn students that the lamp can get very hot!
• (c): Point the heat lamp at a table about 2 ft away. Place two pieces of fabric, one black (I prefer heavy landscape fabric) and the other white, (a cotton t-shirt works well) flat on the table. Underneath each of the two pieces of fabric, place the bulb of a thermometer, and as much of a thermometer (range 0º to 100º C) as you can. As you turn the heat lamp on, have a student read both thermometers to get an initial temperature. Allow the lamp to heat the fabric for at least 10 minutes.

Step 2

• (a): The demonstration! Take a thermometer and hold it in the air above the black fabric and give the class an initial temperature reading. Allow five minutes in the path of the heat lamp and take the temperature reading again. Has the temperature changed? Why? Heat has traveled through the air to warm the thermometer. This is radiation.
• (b): Compare the temperature readings in the two beakers. Why has the beaker in contact with a working heat source gotten hotter? Why hasn’t the beaker over the hot plate that is not turned on gotten hotter? There is no added heat from the plate that is not turned on. The other beaker is getting warmer because it is in direct contact with the heat source. This is conduction-transfer by direct contact.
• (c): As the water over the hot plate gets hot squeeze a drop of food coloring into it along one side. Watch as the drop settles and then begins to diffuse upward. This is convection: heat transfer by movement!

Step 3

• (a): Hold up a mirror and have the students describe what they see. The image is reversed along the vertical plane. Reflection from a plane mirror!
• (b): Take a temperature reading from the thermometers under the fabric. The black fabric has a higher reading because it has absorbed radiant energy from the light. The white fabric has reflected most of the energy. Absorption and reflection!
• (c): Turn off all heat sources!
• (d): Refraction can be demonstrated by using either a prism or a laser shown through a block of Lucite or clear gelatin. In a very dark room, light the laser and let the students note where the light enters the block at an angle that is not 90º. Note that the light appears to bend towards the center line (90º) as the light exits the block; it appears to bend away from the 90º line at the exit. This is textbook refraction. I have had success with this demonstration by holding the block on my whiteboard and having a student assist me by marking the entry and exit lines with an erasable marker.

On the second day, lead the students to the website from Alameda College’s Solar Radiation Learning Module and have the students work through the very good tutorial found there. The module has three parts. If the students are thorough in their approach, they should complete the module’s three parts in two days. What is particularly good about this module is that after demonstrating the methods of heat transfer and light processes, the students see firsthand how they impact the Earth’s energy budget.

Outcome/Assessment:

When the three sections have been completed by the students, have them complete the Study Guide provided online at by writing the definitions of all of the key terms and writing answers to all of the questions listed in the objectives. There is a 10 question Online Quiz for the student that is reasonably well thought out. You may, of course, use the questions provided in your own test, but I have found the online quiz quite well done and use the results for a quiz grade.

Extensions:

Consider how your students might build on this lesson; offer suggestions for sharing what they have learned with their families and making it part of their world.

Internet Resources:

Keywords include: Energy In the Atmosphere. The specific URLs are:

Classroom Resources:

This lesson, really a tutorial, needs a classroom set of computers with Internet access, an LCD projector.

• 1 heat lamp
• White fabric and black fabric (about 1 square foot of each)
• 3 thermometers (range 0º to 100ºC)
• 2 hot plates
• 2 1000 mL beaker with 800 mL of water
• 1 bottle of red food coloring
• 1 pen-style laser
• 1 block of Lucite or gelatin

Alternately, to complete the heat transfer activities, go to the UCAR activities 5, 6, and 7 for materials and time (roughly three periods) The radiation experiment can double as the absorption demonstration.