In Lesson 3, you were introduced to the chemistry of greenhouse gases. Recall that the impact of a greenhouse gas is determined by three factors:

1. The region of infrared radiation (IR) the gas absorbs and how strongly the gas absorbs IR.
2. The concentration of the gas in the atmosphere.
3. The lifetime of gas molecules in the atmosphere before they are broken down or in some other way removed from the atmosphere.

During this lesson you will explore the different greenhouse gases in our atmosphere in more detail. You will also be introduced to some of the ways in which humanity is affecting the atmospheric concentrations of these key greenhouse gases.