Which statement about infrared radiation and greenhouse gases best describes their effect?

Which statement about infrared radiation and greenhouse gases best describes their effect?

• A. They reflect infrared radiation back into space.
• B. They absorb infrared radiation, trapping heat in the lower atmosphere and on the surface.
• C. They absorb ultraviolet radiation only.
• D. They convert infrared radiation into visible light.

Answer: (B)

The main idea here is how greenhouse gases interact with infrared radiation to change Earth's heat balance. Infrared radiation is the heat energy Earth emits. Greenhouse gases in the atmosphere absorb much of this infrared, so the energy is held in the lower atmosphere and near the surface rather than escaping freely into space. This trapping warms the surface overall. The energy absorbed by the gas is eventually re-radiated as infrared in all directions, including back toward the surface, which keeps the lower atmosphere and surface warmer. The other statements don’t fit. Infrared is not primarily reflected back into space by these gases; it’s absorbed. The gases don’t mainly absorb ultraviolet radiation. And they don’t convert infrared into visible light.

The main idea here is how greenhouse gases interact with infrared radiation to change Earth's heat balance. Infrared radiation is the heat energy Earth emits. Greenhouse gases in the atmosphere absorb much of this infrared, so the energy is held in the lower atmosphere and near the surface rather than escaping freely into space. This trapping warms the surface overall. The energy absorbed by the gas is eventually re-radiated as infrared in all directions, including back toward the surface, which keeps the lower atmosphere and surface warmer.

The other statements don’t fit. Infrared is not primarily reflected back into space by these gases; it’s absorbed. The gases don’t mainly absorb ultraviolet radiation. And they don’t convert infrared into visible light.