The Greenhouse Effect: Warming the Earth

Greenhouse effect

Image courtesy of U.S. National Park Service.

The Earth receives large amounts of energy from the Sun in the form of sunlight. Plants convert this energy into fuel for growth, in turn becoming food for many other animals. This energy (called solar radiation) warms our planet, stirs the atmosphere into motion, and drives our weather systems causing winds to blow, clouds to form, and rain and snow to fall.

Water vapor, carbon dioxide (CO2), and certain other gases in the atmosphere allow sunlight to pass through to the Earth’s surface. These same gases prevent infrared radiation (emitted by the Earth) from escaping back into space, thus trapping heat near the Earth’s surface. This is called the greenhouse effect because it resembles the way in which a garden greenhouse traps heated air.

The greenhouse effect is a natural process that keeps the Earth’s atmosphere at a temperature that is comfortable for most living things. The Earth’s average surface temperature is 15°C or 59°F. Without the greenhouse effect, much of Earth’s heat energy would be lost to space. The average surface temperature would be -18°C (0°F), significantly colder than it is now.

Our Experiment

In this activity you will demonstrate how the greenhouse effect warms the Earth. A glass bowl placed upside down on a grassy surface and exposed to sunlight represents gases and clouds in the Earth’s atmosphere; the grassy surface represents the Earth’s land surface. By measuring the air temperature inside and outside the bowl over 15 minutes, you can observe any differences caused by covering part of the grass with a glass bowl. You can work in groups of at least two or three on this project.

Note: This activity works best on a sunny day.

Tools and materials

Two alcohol thermometers
Clear glass bowl, big enough to cover one of the thermometers. A large, empty glass jar can work as well.
Stopwatch
Notebook
Pen
Hand magnifying glass (optional)

What to do

Set up a table similar to the one below in your notebook.

Time (minutes)	Outside temperature (°C)	Inside temperature (°C)	Predicted inside temperature (°C)
Start
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15

Place the thermometers in a grassy place in the Sun. When they both read the same temperature record this reading as the “Start” temperature in the first row of your notebook table. (Tip: It might be easier to read the thermometers with a hand magnifying glass.)
You are going to cover one thermometer with the clear glass bowl; how do you think the temperature under the glass bowl will change over 15 minutes? In the table’s “Predicted inside temperature” column, write down your predictions.
Place the bowl over one of the thermometers. The other thermometer should be next to the bowl but not underneath it. Make sure that no shadows are touching either thermometer.
Start your timer immediately and record the readings from the two thermometers once a minute for the next 15 minutes.
How did your results compare with your prediction?
Draw a graph that shows the temperature of the air inside and outside the bowl over time.
Explain your results.

Reflection questions

In what ways does the Earth’s atmosphere act like the glass bowl?
How would you redesign this experiment to better resemble the Earth’s atmosphere and surface?
Can you think of ways to lower the temperature inside the glass bowl without removing any of the air? What processes in the atmosphere would this represent?
How might you use technology with this activity?

Digging Deeper

Find out more about
the greenhouse effect and global climate.

Compare your greenhouse effect results to ours.

Result/Solution(s)

We measured the temperatures every minute but found that they stabilized after only 10 minutes. Here is the table with our results.

Time (minutes)	Outside temperature (°C)	Inside temperature (°C)	Predicted inside temperature (°C)
Start	17	17	17
1	17	19	17
2	16	20	17
3	16	21	18
4	15	22	18
5	15	23	18
6	15	23	19
7	15	23	19
8	15	23	19
9	15	23	20
10	15	23	20
11			20
12			21
13			21
14			21
15			22

Our data showed that the temperature outside the bowl remained more or less stable, while under the bowl the temperature increased quickly and then leveled off.

In this experiment the glass bowl mimics the Earth’s atmosphere. Sunlight passes through the glass and is absorbed by the grassy surface, causing it to heat up. The warming surface then releases energy, which heats the surrounding air. The heated air inside the bowl is trapped and is unable to mix freely with the cooler air outside the bowl. In this way, the glass bowl acts as a barrier to escaping heat, thus increasing the temperature inside the bowl.

Do not worry if your results are not the same as ours, since the results depend on local conditions. You should, however, see the temperature inside the bowl increasing over time in some fashion.

Watch our animated version of how the greenhouse effect works. As you watch the animation, look for the following:

Describe the movement of solar energy (electromagnetic waves emitted by the Sun).
Describe the movement of infrared radiation (electromagnetic waves emitted by the Earth).
What happens to the solar energy when it passes through the carbon dioxide (CO2) molecules?
What happens to the infrared radiation when it passes through the CO2 molecules?
Based on what you have learned in the activity, how does this animation demonstrate the greenhouse effect?

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Experiment