What are two common examples of naturally occurring greenhouse gases?

• A. Carbon dioxide and water vapor
• B. Methane and chlorofluorocarbons
• C. Oxygen and Nitrogen
• D. Hydrogen and Helium

Answer: (A)

Greenhouse gases are those in the atmosphere that absorb infrared radiation and trap heat, helping keep the surface warmer than it would be otherwise. Two common gases that occur naturally and play this role are carbon dioxide and water vapor. Water vapor is the most abundant natural greenhouse gas and acts as a climate feedback: when temperatures rise, more water evaporates, adding more heat-trapping gas and amplifying warming. Carbon dioxide comes from natural processes like respiration, decay, volcanic activity, and weathering, and it’s present in the atmosphere even without human activities, though human emissions add to it. The other options mix gases that aren’t both naturally occurring greenhouse gases: chlorofluorocarbons are human-made compounds, and while oxygen and nitrogen are the dominant atmospheric gases, they are not the primary greenhouse gases considered in climate contexts; hydrogen and helium are not greenhouse gases. So carbon dioxide and water vapor are the best examples of naturally occurring greenhouse gases.