What is the Greenhouse Effect? - Definition & Impact

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  • 0:00 What Is the Greenhouse Effect?
  • 1:52 Impact of the…
  • 2:22 Global Warming: Impact…
  • 3:20 Lesson Summary
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Lesson Transcript
David Wood

David has taught Honors Physics, AP Physics, IB Physics and general science courses. He has a Masters in Education, and a Bachelors in Physics.

Expert Contributor
Amanda Robb

Amanda holds a Masters in Science from Tufts Medical School in Cellular and Molecular Physiology. She has taught high school Biology and Physics for 8 years.

After completing this lesson, you will be able to explain what the greenhouse effect is, how it works, how significant it is on Earth, and how humans have affected it. A short quiz will follow.

What Is the Greenhouse Effect?

The greenhouse effect is the trapping of the sun's heat in the atmosphere of a planet by gases in that atmosphere. It's called the greenhouse effect because it has a lot in common with how the glass of a greenhouse traps heat inside: heat can get into the greenhouse, but has more trouble leaving.

The greenhouse effect happens because of so-called greenhouse gases, which include carbon dioxide, methane, water vapor, and others. The biggest components of the atmosphere, nitrogen and oxygen, are not greenhouses gases.

The amount of greenhouse effect present on a planet has a big impact on the temperature of that planet. For example, Venus is super hot and has a runaway greenhouse effect that's more intense than any in the solar system. On the other hand, Mars has very little atmosphere at all, and it's super cold there.

The exact process works like this: energy from the sun in the form of visible and ultraviolet light arrives at the earth and enters the atmosphere. The atmosphere is transparent to these wavelengths of light, so it comes straight through without difficulty. Once on the earth, this radiation is absorbed by the surface of the earth and any objects that happen to be on it.

The Greenhouse Effect
The Greenhouse Effect

This energy is later re-emitted by the earth's surface, but it's not re-emitted as visible light or ultraviolet, but as infrared. The gases in the earth's atmosphere are not transparent to infrared, so as it heads up towards space, it is stopped - absorbed - by the greenhouse gases in the atmosphere. Nothing that absorbs energy keeps it forever, so the greenhouse gases do release this energy again, but they release it in every direction equally: some of it heads towards space and leaves, but some of it is emitted back down towards the earth; and this process, where the gases bounce some of the energy back to Earth, is what causes the earth to be as warm as it is.

The Transparency of the Atmosphere at Different Wavelengths of Light
The Transparency of the Atmosphere at Different Wavelengths of Light

Impact of the Greenhouse Effect

The greenhouse effect is hugely significant. Without it, we wouldn't be able to live on Earth. It's believed that the greenhouse effect increases the temperature of the earth by approximately 33 degrees Celsius. This is an astonishing difference in temperature, and should the greenhouse effect end tomorrow, humans (and most of the life on the planet) would likely go extinct.

So, the greenhouse effect is wonderful! We should be thankful it exists. But there are downsides, and one of those downsides is the impact that humans can have on it.

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Additional Activities

Build Your Own Greenhouse

In this activity, students will be using recycled plastic bottles to build their own greenhouse. To complete the activity, you'll need a plastic bottle, two thermometers, a small plant or seeds to grow, soil, a pot or cup, water and ample sunlight.

The Greenhouse Effect

Now that you understand the greenhouse effect, we're going to put it into action by building our own greenhouse out of a recycled plastic bottle. We're going to try growing some plants and compare the temperature inside the greenhouse to outside over time.

  1. Start by getting a clean two liter plastic bottle. Cut the bottle nearly all the way around, about 4" from the bottom, except leave about one inch uncut so that you have a "lid" made of the top part of the bottle.
  2. Next, get a small container that will fit inside the plastic bottle and fill it nearly to the top with soil.
  3. Plant your seeds or plant in the center of the soil.
  4. Place your cup with the plants inside the bottom of the plastic bottle.
  5. Add the thermometer to the soil.
  6. Water your plants and cover them with the top of the plastic bottle.
  7. Allow your plants to rest in the sunlight for several days. Check on them each day to water them and record the temperature over five days in the greenhouse compared to the outside air. You can make a table like the one below to record your observations:

DayTemperature in the GreenhouseTemperature outside the greenhouse


  1. How did the greenhouse temperature compare to the temperature outside the greenhouse over time?
  2. How did our greenhouse act as a model for the greenhouse effect in the atmosphere?
  3. What part of the greenhouse acted like carbon dioxide in the atmosphere and why do you think that?
  4. Why is the greenhouse effect important for life on Earth based on what you saw in our greenhouse model? Include observations from your experiment to support your claim.

Expected Results

Students should notice an increase in greenhouse temperature over time, due to the greenhouse effect. The plastic acts like greenhouse gases in the atmosphere because it traps the heat in the greenhouse, just like the gases do in the atmosphere. Although a runaway greenhouse effect is bad, some greenhouse effect is necessary to warm our planet and support life.

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