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.
