Which greenhouse gas is most abundant in Earth's atmosphere?

• A. Water vapor (H_2O)
• B. Methane (CH_4)
• C. Nitrous oxide (N_2O)
• D. Carbon dioxide (CO_2)

Answer: (A)

Verified step by step guidance

1. Understand that the question asks for the most abundant greenhouse gas in Earth's atmosphere, which means identifying which gas contributes most significantly to the greenhouse effect by its concentration.
2. Recall that greenhouse gases include water vapor (H\_2O), carbon dioxide (CO\_2), methane (CH\_4), and nitrous oxide (N\_2O), among others.
3. Recognize that water vapor is naturally the most abundant greenhouse gas because it is present in large amounts due to evaporation from oceans, lakes, and other water bodies.
4. Note that while carbon dioxide, methane, and nitrous oxide are important greenhouse gases, their concentrations are much lower compared to water vapor.
5. Conclude that water vapor (H\_2O) is the most abundant greenhouse gas in Earth's atmosphere based on its natural abundance and role in the greenhouse effect.