Which gases are recognized as greenhouse gases contributing to Earth's infrared trapping?

• A. Carbon dioxide, methane, and water vapor
• B. Oxygen, nitrogen, argon
• C. Helium, neon, krypton
• D. Carbon monoxide, sulfur dioxide, ozone

Answer: (A)

Greenhouse gases trap heat by absorbing infrared radiation that would otherwise escape back to space. The gases that dominate Earth's infrared trapping are carbon dioxide, methane, and water vapor. Water vapor is the most abundant of these and acts as a feedback: as temperatures rise, more water vapor enters the atmosphere, which amplifies warming. Carbon dioxide and methane, though present in smaller amounts, have strong absorption bands in the infrared and remain in the air for long periods, making them major drivers of climate forcing from human activities and natural sources. Other gases like oxygen, nitrogen, and noble gases don’t significantly absorb infrared and thus don’t contribute much to the greenhouse effect. While some gases such as ozone, carbon monoxide, and sulfur dioxide can affect infrared absorption in specific conditions, they are not the primary globally significant greenhouse gases in the same way as the trio above.