Which greenhouse gas is the most dominant in the atmosphere under natural conditions?

Which greenhouse gas is the most dominant in the atmosphere under natural conditions?

• A. Carbon dioxide
• B. Water
• C. Methane
• D. Nitrous oxide

Answer: (B)

Water vapor dominates the natural greenhouse effect because it is by far the most abundant greenhouse gas in the atmosphere and it absorbs infrared radiation very efficiently across many wavelengths. Its concentration can be quite high, especially in warm, humid air, so it traps a large amount of heat near the surface and in the lower atmosphere. The other greenhouse gases—carbon dioxide, methane, and nitrous oxide—are present in much smaller amounts, so their direct contribution to the natural greenhouse effect is smaller. An important nuance is that water vapor acts mainly as a feedback: warming increases evaporation and humidity, which then amplifies warming further.

Water vapor dominates the natural greenhouse effect because it is by far the most abundant greenhouse gas in the atmosphere and it absorbs infrared radiation very efficiently across many wavelengths. Its concentration can be quite high, especially in warm, humid air, so it traps a large amount of heat near the surface and in the lower atmosphere. The other greenhouse gases—carbon dioxide, methane, and nitrous oxide—are present in much smaller amounts, so their direct contribution to the natural greenhouse effect is smaller. An important nuance is that water vapor acts mainly as a feedback: warming increases evaporation and humidity, which then amplifies warming further.