Video: Identifying Greenhouse Gases

Which of the following are greenhouse gases? [A] Carbon dioxide. [B] Oxygen. [C] Nitrogen. [D] Argon. [E] Methane.

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Video Transcript

Which of the following are greenhouse gases? a) Carbon dioxide. b) Oxygen. c) Nitrogen. d) Argon. e) Methane.

As we get started answering this question, let’s remind ourselves just what a greenhouse gas is. If we consider the system of our Earth and the atmosphere surrounding it, then there’s a normal thermal process that goes on as sunlight reaches the Earth. As light comes from the sun and lands on the surface of the Earth, the Earth heats up in response. This heat is then radiated off the surface of the Earth and back out through the atmosphere and then into space. This is how the process would work unless there’s something in the atmosphere that blocks the heat from escaping.

It’s possible for there to be certain gases in the atmosphere so that exactly this happens. The heat that normally would escape from the Earth out into space is reflected back towards Earth. These gases, because they let sunlight pass through them but they block heat trying to escape, are known as greenhouse gases. That is, they work very much the same way that a greenhouse works for keeping plants warm. So, a greenhouse gas is an atmospheric gas that’s responsible for blocking the radiation of heat.

When we think about Earth’s atmosphere, the most common gases in that atmosphere are, in order, nitrogen, then oxygen, and then argon. None of these gases are responsible for trapping heat inside Earth’s system. On the other hand, the gas carbon dioxide, symbolized CO₂, is the second most common greenhouse gas after water vapor. And then, answer option e, methane, is also a known greenhouse gas. It’s a gas that effectively traps heat inside Earth’s atmosphere. So, in answer to our question, we choose answer options a and e; carbon dioxide and methane are both greenhouse gases.

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