Activity 5 (Explore/Explain): Urban Heat Islands
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In this activity, students perform a series of experiments that show how different surfaces affect how much heat is absorbed by the Earth, which contributes to the urban heat island effect. While the urban heat island effect does not directly contribute to climate change or sea level rise, temperatures in urban areas are affected by both urban heat islands and climate change, resulting in dangerously high temperatures. Consider adding this activity if your school is in an urban area or your students live in an urban environment.
Activity Objectives & Materials
Approximate Time: 2 class periods (90-120 minutes)
Students will be able to explain the Urban Heat Island effect
Students will perform experiments to explain one cause of the urban heat island effect.
Materials (see activity for details on these materials)
Computer & projector
Black and white construction paper
Other “surface” materials: soil, grass, rocks, sticks, sand, roof shingle, water, etc.
Stopwatch (at least one)
Clipboards (optional, for recording data outside)
Graph paper (optional)
What is Causing the Ocean to Rise?
DCI: ESS 3.D: Global Climate Change
SEP: Planning & Carrying Out Investigations
CCC: Cause & Effect
Have you ever walked barefoot on hot pavement during the summer? What was it like? What other surfaces get very hot in the summer? What surfaces stay cooler?
Hot surfaces: sand, rocks
Cool surfaces: grass, dirt
1. Frame the Activity
Ask students if they think the surfaces they talked about in their warmup have any effect on the temperature of the atmosphere. Tell them that today they’re going to design experiments to test their answers.
2. The Urban Heat Island Effect
Go to the climate.gov website for the DC/Baltimore heat island effect and show students one of the maps (see example to the right). You may want to zoom out so students can see the whole map. Make sure they understand the temperature scale at the bottom, and move the slider back and forth. Ask students what they notice about where the temperature seems to be hotter or cooler. It should be relatively easy for students to recognize that the temperature is hotter where there is pavement, and cooler where there is grass and trees.
Tell students that scientists call this the “Urban heat island” effect. It is called a heat island because the high temperature air is like an island surrounded by cooler air. They are urban because they are mostly found in cities. Ask students why they think they are mostly found in cities (because cities have a lot of pavement).
Ask students why they think urban heat islands can be harmful (temperatures can get well over 100° in the summer).
3. Introduce the Experiment
Tell students that to test their ideas about what causes the urban heat island effect, they are going to do a series of experiments. Each group of students will do a different version of the experiment so that they can compare their results. Pass out the Urban Heat Island Effect sheet to students.
For their experiments, they will measure the air temperature near different surfaces to see if they have different temperatures. Ask students what kinds of things they could use to act as different surfaces. If they get stuck, remind them of the surfaces they talked about during their warmup. As students share ideas, write them down on chart paper or on the board. You can also ask about how they could represent specific things such as a roof or the ocean.
4. Writing Research Questions
Form students into groups, and have each group choose a surface that they will test. It is best if they all choose different surfaces so they can compare their results. From here, have students write a research question based on comparing their material to another material. For example, if students are using the black paper to represent pavement: “Does a dark surface cause the temperature to get higher than a light surface?” If students are new to writing research questions, you may want to write one together and then have them write their own questions in groups.
Review the materials list with students, and have them add any additional materials that they are going to use such as soil, grass, or black paper.
Modification: If there are different surfaces near the school that have the same sun exposure, students can measure the air temperature near these. Just make sure there are no other variables (ex. shade, wind, etc.) that may affect the results.
In order for students to be able to compare results from their tests, they all need to agree on the same procedure. This experiment is relatively simple, so their procedure should consist of a few steps:
Put “surface” materials in a sunny area.
Hold the thermometer a given distance above the surface (ex. 1 inch)
Leave the surfaces outside 10-20 minutes (have students decide on a time)
Record the temperature of the air every 1-2 minutes (have students decide on a time)
Have students write their procedure on their handout, including any additional steps. If it appears to be windy outside, consider how you will modify the procedure to prevent the wind from affecting the results.
Modification: Showing the Greenhouse Effect: To simulate the greenhouse effect, you can also run the experiment using a jar with the thermometer inside. Because the air is trapped inside the jar (the “greenhouse”) the temperature will likely be significantly higher than their surface measurements. If you do this variation, be sure to clarify for students the difference between the greenhouse effect and urban heat islands, and how the jar is only simulates the greenhouse effect.
7. Variables and Controls
Have students fill in the variables and controls for their experiment. The independent variable is their surface, the dependent variable is the temperature, and the controls are the location of the surfaces.
8. Write a Hypothesis
Have students write a hypothesis about how the temperature near their surface will change compared to one or more of the other surfaces. Their hypothesis should be an answer to their research question. Make sure students are thinking about their hypotheses so they are logical. For example, ask them if they think dark surfaces heat up more than light surfaces?
9. Build the Setups
Have students gather their materials. You may want to have them use trays or other containers to make the materials easier to carry. As they work, check to make sure the setups are the same except for the material that will act as the surface.
10. Run the Experiment
Take the setups outside (or put them in a sunny location if you cannot go outside. Make sure to have students record the temperature at the exact intervals they have determined in their procedure. You can give each group a stopwatch, or use one stopwatch for the whole class and have them all take the temperature at the same time. Students should record their data in the Surface 1 space on their data table.
Teacher Tip: Students sometimes struggle to make accurate thermometer readings if you are using alcohol thermometers. It is a good idea to practice reading a thermometer before going outside to collect data, and checking on students’ measurements if you think they will have difficulty.
11. Data Sharing
Have students share data with groups that they have chosen to compare with. For example, if one group used a light surface and other group used a dark surface, or sand vs. grass, have them share data with the group that is using their comparison material. You may also want students to compare data from all the surfaces. If so, put all the data into a computer spreadsheet or on the board for students to copy. Have them write their comparison group data into the Surface 2 space on their data table.
12. Data Analysis
When students have collected all their data, return inside to have them do their analysis. They should start by finding the difference between the final and ending temperatures to see how much the temperature changed. You can also have them graph their data in a variety of ways: ex. bar graphs with the temperature change for each surface, or time vs. temperature line graphs. Make sure the graphical representation you choose is meaningful for the analysis.
13. Sensemaking Discussion
Have students share what they learned from their experiments. Use some or all of the questions below to help drive student thinking, but make sure that students are doing most of the talking, and make sure they are referencing their data. It will help for this if the data is visible somewhere in the classroom:
Which surface seemed to cause the temperature to rise the most? The least?
Were you right or wrong in your hypotheses?
Are the surfaces that caused the temperature to rise the most similar or different in any way?
What do your results help you understand about the urban heat island effect?
14. Return to Correlation & Causation
Ask students if they think urban heat islands are raising the global temperature (is one causing the other?). Students can make logical arguments on both sides (ex. if more heat is absorbed, more will be trapped, and that will raise temperatures). However, in reality, global heat islands do not trap nearly enough heat to raise global temperatures. They are correlated because as global temperatures increase, urban heat island temperatures also go up, but the cause of global temperature increases is the greenhouse effect, and the cause of urban heat islands is related to the types of surfaces in urban environments (as well as other factors). The only cause-effect relationship present is that when temperatures get hot in cities due to urban heat islands, people in those cities tend to use more electricity to cool the air, which does cause higher global temperatures (due to increased greenhouse gases being emitted to produce the electricity).
The Urban Heat Island Effect & Ozone Formation: Ground-level ozone, an air pollutant that can irritate lungs and make breathing difficult, is formed by a chemical reaction that occurs in the presence of hot weather and sunlight. Another effect of the urban heat islands is an increase in ozone production due to increased temperatures.
15. Conclusion (Formative Assessment)
Have students complete the conclusions section of their experiment handout. The second question asks students why the air in some jars heated up more than others. After their discussion, students should be able to explain that some surfaces absorb more heat than others, and therefore heat up the jar more than others.
The final question asks students to explain the urban heat island effect using their results. Students should be able to explain that there are more surfaces in urban areas that absorb a lot of heat, and therefore they raise the temperature in urban areas more.
Urban heat islands are complex: Urban heat islands are caused by more than just differences in surfaces. Large numbers of tall buildings can trap heat by slowing wind and acting as large heat sinks. Larger populations also add more heat to the air through the use of cars, air conditioning, and other machinery.
The effects of urban heat islands also go beyond higher temperatures. With higher temperatures come increase ozone levels (see the note above), and increased electricity demand for things like air conditioner. This increased electricity demand often results in additional greenhouses gases being released to the atmosphere, which accelerate climate change.