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
Instructor: 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.

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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