Exploring Albedo

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Objective

SWBAT use a model to explore reflectivity of certain Earth surface materials.

Big Idea

In this lesson students experiment with different Earth surface materials to determine how reflective they are.

Getting Started

In the lab activity, students explore the heating and cooling rate of different Earth materials in order to answer the question

"How does the surface type and moisture content affect the surfaceʼs temperature?"

Working in pairs, students select two materials to test and compare. Their results are shared with the class and compared to all other results in order to make a conclusion. 

The goal is to reach a class consensus on the reflectivity (albedo) of Earth materials and connect that to changes in Earth atmosphere. 

Materials (for a class of 20-25 students)

  • 5-6 heat lamps
  • 20-25 clear plastic pint containers (or similar)
  • plastic wrap
  • 20-25 thermometers
  • water
  • salt
  • soil (different types if available)
  • sand (different types if available)
  • ice
  • snow (if available in season in your area)
  • gravel

Engage

10 minutes

I begin the class by reviewing previous taught concepts about the uneven heating of Earth's surface. (You can refer to another lesson of mine on the Greenhouse Effect and heat transfer via radiation. In that lesson students explored the rate which soil and water heat and cool with and without an atmosphere.)

I ask students what they think the rate of heating would be if the surface materials are lighter in color than the soil (sand) and the water (ice/snow). I ask them to share their ideas and make some causal predictions. 

In addition, I created the Reflected or Absorbed? Albedo Probe to give to students and discuss. It is modeled on the Page Keeley's series, Uncovering Student Ideas in Science

Explore Day 1

40 minutes

If time is a constraint, you may opt to only teach this part of the lesson. In part 2, students are given more variables to explore and test but you can cover the main ideas about albedo with just this lab. 

In this lab students examine the effect of various types of “surfaces” on the time rate of change of temperature of those surfaces when they are exposed to incident “sunlight”. Both surface reflectivity and moisture content impact the amount of incident radiation that is used to change the surface’s temperature. For example, if the surfaces are highly reflective, then little of the incident radiation would be absorbed and used to warm the surface.

They take temperature readings just below the surface with a thermometer and at the surface using an infrared thermal gun. (Note: you can pick one of these up at Home Depot or on Amazon for less than $20.00. If you have the budget, grab 2-3.)

Albedo is defined as the fraction of incident energy that is reflected.

In this experiment, the mass and specific heat of the two containers of dry sand will be the same since they contain the same amount of sand in identical containers, only the sand color is different.

Materials

  • Heat lamp w/reflector
  • Light sand
  • Dark sand
  • Cups  (x4)
  • Thermometers
  • IR Gun 
  • water 

Predict:

Ask students to make a prediction about the change in temperature over time of the two cups of sand. Which will get warmer? Which will rise fastest? Why?

Discuss their ideas, then review the lab procedure. Walk them through the steps and safety protocols then get to work!

Procedure:

1. Place about 1.5 inches of sand in two white styrofoam cups, one with dry black sand and the other with dry white sand. Use water at room temperature to dampen the sand. (NOTE: This may have been done for you.)

2. Using both the thermometer and the infrared gun, measure the temperature of the sand initially. They should be about the same temperature at the start of the experiment.

3. Place the reflector lamp equal distance (as close as practical) above the two cups. As above, it is very important that the two cups receive the same intensity of incident radiation so align the cups as above.

4. Now turn on the lamp. Again using both the thermometer and the infrared gun, measure and record the temperatures of the sand in each of the two containers at three-minute intervals for fifteen minutes.

 5. Take the readings by turning off the lamp while you are taking the temperature of the sand:

  • Place a thermometer in the sand in each cup, i.e., you need two thermometers.
  • The thermometer should be inserted until all of the bulb is below the surface of the sand.
  • Be sure the thermometer has come to thermal equilibrium with the sand before recording the temperature.
  • Do not leave the thermometers in the sand between measurements; insert the thermometer in the sand for each reading.

 

Explore Day 2

45 minutes

Day 2 (optional)

On the second day of this lesson, students repeat the procedure from our first day. However, they compare two different materials. Students write their question, prediction, reasoning, materials list and procedure in their science journals. They also create a data table with labels for each row and column. 

Give them a range of materials to choose from such as:

  • dry/wet soils
  • salt/fresh water
  • sand/gravel
  • ice/soil
  • ice/snow

Discuss where on Earth you might find surface conditions that are representative of the different materials. 

Once they have their question, prediction, reasoning, materials list and procedure, students must check with me. I conference with each group and help them tighten up their procedure before starting. Make sure to cover your safety protocols with regards to the heat lamps. 

Manage your time here. Students need 15 uninterrupted minutes of data collection. If everything is in order they can start. 

When students are finished have them report out their data on a large chart for the class to see, then clean up their stations. 

Explain

15 minutes

Once all the data from the classes is up, hand out the summary questions below and give students time to work with the data to complete them. 

1. Which material absorbed more heat in the first 15 minutes?

2. Imagine that it’s summer and that the sun in shining on the ocean and on a stretch of land. Which will heat up more during the day? Which will cool more slowly at night? Explain.

4. How do you think the surface of the materials heated up?

5. How do you think material below the surface heated up?

6. What properties of the earth materials may have caused them to heat and cool at different rates?

7. How would the uneven energy absorption by different surfaces on earth (water, soil, snow, trees, sand, etc.) affect the atmosphere?

 

This 120 Seconds of Science with Doc Ryan video offers a great "in the field" explanation

 

In the video below, one of students reflects how this lesson helped him make meaning of how albedo is a part of the climate change story.