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Human Energy Systems | Activity 3.2

Activity 3.2: The Greenhouse Effect (20 min)

Students share their ideas about climate change through an anonymous assessment and discuss the connection between the greenhouse effect and global warming.

Resources Provided

Setup

Prepare a computer with a projector to display the PPT. If you would like to survey your students (optional) prepare one computer with an internet connection for each student.

Directions

1. Introduce the activity.

Display slide 1 of the 3.2 The Greenhouse Effect PPT. Tell students we spend a lot of time discussing the Keeling Curve in this unit, but why is this important? Ask students for their initial ideas: “Does anyone have an idea about why scientists might care so much about the Keeling curve?” It is important for understanding how increasing CO2 in the air is connected to global climate change.

Assessment

Formative Assessment: Listen for students’ initial ideas about how atmospheric CO2 and temperature are connected. Do they see a causal relationship? At this point, they may have many unanswered questions about how increasing greenhouse gases in the atmosphere lead to climate change. However, at the end of this activity, they should have a good understanding of how increasing greenhouse gases in the atmosphere lead to warmer temperatures as a result of the greenhouse effect. If the students are still having trouble making this connection, you may want to show the students different models of the greenhouse effect, or revisit the slides in the PPT that help explain this phenomenon.

Tips

If you choose to have students take the optional survey in step 7, you may want to ask students to turn in their results anonymously. This will give you an assessment of the range of attitudes in your classroom, but will not stigmatize individuals based on their profile results.

Modifications

Ask students to share with the class their ideas about why increasing levels of carbon dioxide in the atmosphere is related to additional Earth systems other than temperature (e.g., sea level rise, arctic sea ice melt).

Extending the Learning

Encourage students to watch for references to climate change or global warming in the newspapers, magazines, and other media. Ask them to be “critical consumers,” and to consider the sources of the information. Does the author/speaker provide evidence to support the claim? What evidence does the author/speaker provide?

Advanced students may find it interesting to research differences on the Earth in the past when carbon dioxide levels and temperature were at their highest. What animals and plants lived on the Earth then? What was the climate like?

Some students may have questions about how infrared radiation interacts with greenhouse gas molecules to produce heat. Although we do not go into this amount of detail in this unit, students may find these resources helpful:

1It is possible that some students will challenge the claim that climate change is caused by humans by pointing to natural cycles in the Earth’s history, claiming that the current highs are due to this natural cycle. Try to help them understand that part of what they are saying is true: Earth does have a history of CO2 and temperature fluctuations. However, this does not contradict the scientific evidence for anthropogenic climate change: the current increase of CO2 and other greenhouse gases in the atmosphere is a result of human use of fossil fuels and deforestation, which has caused the global temperature to rise 0.8° C (1.4° F) since 1900. That might not sound like a lot, but that is almost 10x faster than any other naturally occurring warming period in Earth’s history.

2The fact that the greenhouse gases trap infrared radiation is key. Some students may wonder why the light energy from the sun is not “trapped” on the way in, but it is trapped on the way out. The reason for this is that the light energy from the sun enters the atmosphere in the form of short-wave radiation. This can pass through the atmospheric particles without being trapped (although on the way in, some of this radiation is reflected by the earth and particles in the atmosphere). However, when this short-wave radiation meets the Earth’s surface, it is returned to the atmosphere in the form of infrared radiation, which is long-wave radiation. Some of this infrared radiation (heat) is trapped by greenhouse gases, which keeps the Earth’s lower atmosphere and surface warm. Some of this infrared radiation (heat) goes back into space.

3Note that from this graph alone, it is not possible to identify a causal relationship between temperature and CO2 levels (i.e., this graph doesn’t indicate that the rise of CO2 is causing the temperature rise, or vice versa). However, when combining the information in this graph with what students know about the greenhouse effect, they should be able to infer that increased levels of CO2 in the atmosphere does, in fact, cause temperatures to rise by trapping more infrared radiation in the atmosphere.