Which gas is primarily responsible for the natural warming of the lower atmosphere?

• A. Methane
• B. Water vapor (H2O)
• C. Carbon dioxide
• D. Nitrous oxide

Answer: (B)

Water vapor is the main driver of natural warming in the lower atmosphere because it is present in the highest amounts among greenhouse gases and is very effective at absorbing infrared radiation. When the surface warms for any reason, evaporation increases, adding more water vapor to the air. Since water vapor itself traps heat, this extra amount creates a positive feedback: more warming leads to more water vapor, which leads to even more warming in the troposphere. Other gases like methane, carbon dioxide, and nitrous oxide do contribute to warming, but their overall influence is smaller in this natural warming context due to lower concentrations and less potent feedback compared to water vapor.