Carbon dioxide, CO2, is an important greenhouse gas. Greenhouse gases warm the Earth primarily by:

Question

BlackTom AI · Accepted Answer

Greenhouse gases trap outgoing longwave (infrared) radiation: CO2 absorbs infrared emitted by the warmed Earth and re-emits it, warming the surface and lower atmosphere.

1) Relevant knowledge points and concepts
- Solar radiation reaching Earth is mostly shortwave (visible/UV); Earth absorbs much of it and re-emits energy as longwave infrared (IR).
- Greenhouse gases (CO2, H2O, CH4, N2O) have molecular vibrational modes that absorb IR at specific wavelengths (CO2 strongly near 15 μm).
- After absorption, these gases re-radiate IR in all directions, including back toward the surface, raising the equilibrium temperature (the greenhouse effect).
- Radiative balance: absorbed solar ≈ emitted IR; adding greenhouse gases reduces outgoing IR to space until the surface warms enough to restore balance.

2) Step-by-step reasoning
- Step 1: Sunlight (shortwave) passes largely through the atmosphere and warms Earth’s surface.
- Step 2: The surface emits that absorbed energy as longwave infrared radiation.
- Step 3: CO2 molecules absorb some of this outgoing infrared at characteristic wavelengths.
- Step 4: Absorbed energy is re-emitted isotropically; part goes back to the surface, reducing net cooling.
- Step 5: The reduced outgoing IR causes the surface/atmosphere to warm until a new radiative equilibrium is achieved with more outgoing IR at a higher temperature.

3) Calculations
- No numerical calculation is required for this conceptual question. The qualitative radiative-balance mechanism above suffices.

4) Why the correct answer is correct
- The core mechanism of greenhouse warming is absorption and re-emission of Earth's infrared by gases like CO2; this is exactly what “Absorbing some of the infrared radiation emitted from the Earth” states.

5) Why other options are incorrect
- “Absorbing the sunlight reflected from snow…” describes albedo effects (reflection), not greenhouse gas IR absorption. 
- “Making politicians mad…” is irrelevant and humorous, not scientific. 
- “Breaking down the methane emitted by flatulent cows” is false: CO2 does not cause methane breakdown in the atmosphere as its warming mechanism. 
- “Breaking down the ozone layer that cools the planet” is incorrect: ozone chemistry and stratospheric heating are different processes; CO2’s primary warming action is not via destroying ozone.

6) Conclusion
Therefore, the correct answer is “Absorbing some of the infrared radiation emitted from the Earth,” which matches the provided answer.

Carbon dioxide, CO2, is an important greenhouse gas. Greenhouse gases warm the Earth primarily by:单项选择题

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