Oxygen (O2) and nitrogen (N2) do not have much greenhouse effect, but several trace gases, including carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), and various chlorofluorocarbons, are important greenhouse gases., with CO2 most important in controlling Earth's surface temperature. The primary mechanism by which these greenhouse gases warm the Earth is:

Question

BlackTom AI · Accepted Answer

Absorbing some of the infrared radiation emitted from the Earth.

1) Relevant knowledge points and concepts
- Electromagnetic energy: the Sun delivers mostly shortwave (visible/UV) radiation; the warmed Earth emits longwave (infrared, IR) radiation. 
- Greenhouse gases (CO2, CH4, N2O, CFCs) have molecular vibrational modes that interact with IR wavelengths and can absorb and re-emit that radiation. 
- Radiative energy balance determines planetary surface temperature: incoming solar ≈ outgoing longwave in steady state. Changing the radiative transfer (by adding absorbers) changes the equilibrium temperature.

2) Step-by-step reasoning
- Sunlight passes largely unimpeded to the surface because the atmosphere is transparent to much shortwave radiation. 
- The surface warms and emits IR. 
- Greenhouse gas molecules absorb a portion of this outgoing IR at specific wavelengths, then re-emit radiation isotropically (both upward to space and downward toward the surface). 
- Downward-emitted IR adds energy to the surface–lower atmosphere system, so the surface must warm until outgoing emission balances incoming flux again. That warming is the greenhouse effect.

3) Simple calculation (one-layer atmosphere model)
- Let F_in = S(1−A)/4 be solar flux absorbed; without greenhouse, equilibrium σT_e^4 = F_in. 
- With a single absorbing atmospheric layer that radiates both up and down, the surface receives F_in from the Sun plus downward F_in from the layer, so σT_s^4 = 2F_in, hence T_s = 2^(1/4) T_e ≈ 1.19 T_e (about 19% warmer than the effective radiating temperature).

4) Why the correct answer is correct
- The mechanism above directly describes “absorbing some of the infrared radiation emitted from the Earth,” which is how trace gases increase surface temperature.

5) Why other options are incorrect
- Preventing convection (glass analogy): a real greenhouse’s warming is partly from blocking convection, but the atmospheric greenhouse works primarily by radiative absorption and re-emission, not by stopping convection. 
- Raising atmospheric pressure: while pressure affects temperature locally (adiabatic processes), global warming is not caused by a pressure increase. 
- Making politicians mad: irrelevant and not a physical mechanism. 
- Chemical reactions releasing energy: greenhouse gases warm via radiative transfer, not by frequent exothermic reactions (they are chemically stable in the atmosphere).

6) Conclusion
This explanation confirms the correct answer: Absorbing some of the infrared radiation emitted from the Earth.

类似问题

Which of the following statements concerning greenhouse warming or climate change is FALSE?

There are many greenhouse gases, including carbon dioxide (CO2), methane (CH4). and vaporized water (H2O). These and other greenhouse gases warm the Earth primarily by:

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

What property makes a gas a greenhouse gas?

Regarding the Earth's greenhouse effect and its implications for climate change, which statement is most accurate?

Increased heat from the runaway greenhouse effect evaporates oceans, producing more greenhouse heating. This happened to _ and might happen to _ someday.

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