Seeing the Greenhouse Effect
The greenhouse effect is a central mechanism in climate change. Although many students have heard the phrase, few understand the underlying causes of the greenhouse effect. What combination of factors cause the greenhouse effect to warm earth’s atmosphere? This is at least partially because the greenhouse effect is a multi-step process involving mechanisms we can’t see. When sunlight heats the earth’s surface, we can’t see the warmed earth radiate infrared light. Neither can we see how atmospheric gases block that light from radiating back into space.
We’ve developed a quick demo that uses an infrared camera to demonstrate how different gases block infrared light . The video below shows three students, each with a plastic bag containing a different gas: one bag contains air, one contains carbon dioxide, and the last contains tetrafluoroethane. All three bags appear transparent when viewed with visible light. That means that visible light passes unaffected through all these gases. But when placed in front of an infrared light source, we can see that each type of gas blocks different amounts of infrared light. To test this, we placed bags of gases in front of people’s faces. The infrared light radiating from their warm faces passes through each bag. Some of the infrared radiation is absorbed or blocked by the gas. We can see this with the infrared camera. When the gases block infrared light from the students’ faces, the infrared camera shows this by recording less infrared radiation, and their faces appear colder. The heat from their faces is being blocked by the gas rather than transmitted through.
Watch the video to see the difference between the gases.
When viewed in the visible spectrum, the bags all appear the same: they are all transparent to visible light. Through the infrared camera, however, the differences become obvious. The student holding the bag filled with air looks no different, while the student holding the tetrafluoroethane practically disappears. Tetrafluoroethane is a potent greenhouse gas. It blocks much of the infrared light coming from the student, as it would block nearly all the heat reradiating from the earth. Carbon dioxide falls somewhere between the two, only partially blocking the infrared light. This is indicated by the slight color change on the student’s face. This vividly demonstrates an important part of the greenhouse effect: some gases allow visible light from the sun to pass through the atmosphere and warm the earth’s surface, but block the infrared light emitted from the earth’s surface, causing the atmosphere to warm.
Here’s how you can do this demo with your students. You’ll need to get:
Transparent ziplock bags- We used 18x24 inch Large Roaster Ziplock bags
Air (fill bag using bicycle pump)
Carbon Dioxide Gas (fill using a carbon dioxide cartridge from a bicycle tire filler)
Tetrafluoroethane Gas (available as “Refrigerant 134a” from automotive supply stores)
Infrared Camera (such as the FlirOne Pro)
For this experiment, begin by taking students’ pictures with the infrared camera to use for comparison later. Next, have the students place a bag filled with gas in front of their faces and take their picture again. If the gas blocks infrared light, their face will appear much more cool toned. Have students compare their two photos and observe the differences. Students can see for themselves how different atmospheric gases, such as carbon dioxide, trap heat in our atmosphere.
This effect is both fascinating to watch and important to understand. Accumulating carbon dioxide in our atmosphere continues to trap heat and has a detrimental effect on our global climate. Amidst misconceptions about the science of climate change, simple demos like these become crucial to giving the students an understanding of the science of climate change.
While this demonstration is a good starting point, it only shows part of the greenhouse effect. Other mechanisms, such as albedo, are critical steps to students understanding the greenhouse effect. At Pivot Interactives, we’ve created a complete set of interactive videos and activities that students can use to learn key climate science concepts, such as: the albedo effect, greenhouse effect, how temperature increases cause sea level rise, and how increased temperature causes ocean acidification. Sign up below to be on our mailing list to learn more about this.
So far, we have four activities to help students understand the greenhouse effect:
Greenhouse Effect Part 1: Albedo
A critical mechanism in climate science is albedo. In this activity, students explore how different color surfaces reflect different amounts of light. Students’ own observations and measurements will lead them to see the connection between reflectivity and temperature increase, a key mechanism in the science of climate change.
2. Greenhouse Effect Part 2: Warm Objects and Infrared Emission
The earth’s surface absorbs incoming solar energy, becoming warm in the process. The warm earth then radiates infrared light, allowing some of the sun’s energy to escape back into space. This process achieves the delicate balance that keeps our planet at a habitable temperature.
In this activity, students make observations to understand that when objects warm, they emit infrared light. We can’t see infrared light, but luckily infrared cameras can. In this activity, students observe that an object emits infrared light as it is warmed by a spotlight, and observe that the object continues to emit infrared light even once the spotlight is turned off. This is another key mechanism in understanding the greenhouse effect: the earth’s surface emits infrared light.
3. Greenhouse Effect Part 3: Infrared Light Absorption by Greenhouse Gases
Some gases, like carbon dioxide, methane, and tetrafluoroethane (a common refrigerant) are transparent to visible light, but block infrared light. In this activity, students use an infrared camera to compare the amount of infrared light blocked by different gases. This activity allows students to measure the effect of different heat-trapping gases for themselves.
4. Using an Atmospheric Simulation Chamber to Explore the Greenhouse Effect
In this activity, students can see the greenhouse effect in action. Students create scenarios by selecting a ground color and an atmospheric gas, and measure how the temperature changes when light is shined into the chamber. Students can compare the outcomes of these scenarios to see which combinations cause the most atmospheric warming. This activity can be used to introduce the concept of greenhouse effect, prior to doing the three activities described above, or as a culminating activity, so students can see how the all three mechanisms in the previous activity combine to cause atmospheric warming.
We’re rapidly expanding our collection of activities for earth and climate science, along with environmental science.
Tips for Doing Greenhouse Effect Labs in your Classroom
How about doing your own greenhouse effect lab? We encourage teachers and students to explore and experiment on their own. It’s certainly possible to create hands-on activities to measure the greenhouse effect, but here are some factors to consider:
Using a glass container will skew results because the glass itself is such an effective greenhouse that it will mask the heat-trapping effect of the gases inside. Glass is already so effective at blocking IR that the contents of the gas in the container is unlikely to have a noticeable effect. This is also true for polycarbonate containers such as pop bottles, which, like glass containers, are transparent to visible light but block infrared. These containers are also effective greenhouses, and will make it difficult to see the additional impact of gases like carbon dioxide. In our lab, we constructed a chamber with thin polyethylene walls. Polyethylene is transparent to infrared and visible light, so this chamber lets us isolate the effect of the heat-trapping gases inside.
Water in the container will cause a feedback loop, and potentially cause confusing results. As the container warms, the amount of water vapor increases, blocking infrared light from leaving. The more IR is blocked, the warmer the container, which, in turn, increases the amount of water vapor. This loop also causes increased cooling. As the atmosphere cools, the amount of water vapor deceases, allowing more IR to escape, further cooling the atmosphere and further reducing water vapor. Water vapor in the system will mask the effect of other greenhouse gases, such as carbon dioxide, and cause warming in containers that with non-greenhouse gases, such as oxygen or nitrogen.
Although water vapor is an important factor in greenhouse effect, it’s effect is different than atmospheric gases like carbon dioxide. Water vapor enters and leaves the atmosphere if the temperature change, whereas carbon dioxide remains in the atmosphere and causes warming for many decades regardless of temperature. Water vapor has the effect of amplifying atmospheric heating or cooling, whereas added carbon dioxide causes atmospheric heating. Adding water to experiments meant to show the effects of gases like carbon dioxide or methane can produce confusing results.
Specific heat capacity can affect results. Using different materials, such as metal vs water vs air can cause different heating rates not because of greenhouse effect or albedo, but because different substances change temperature at different rates.
We find that a mixture of hands-on activities, like the one using the plastic bags and infrared camera, combined with experimentation, data collection, and analysis using Pivot Interactives activities is an efficient and effective way to engage students in learning about climate science.