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

Question

BlackTom AI · Accepted Answer

Greenhouse gases trap outgoing infrared radiation, causing the surface to be warmer than Earth's effective radiating temperature — this is the basis for why anthropogenic increases in CO2 are the main climate concern.

1) Relevant knowledge points and concepts
- Solar constant S ≈ 1361 W/m²; planetary albedo A ≈ 0.30.  
- Effective radiating temperature T_eff is set by balance of incoming and outgoing radiation.  
- The natural greenhouse effect raises the surface temperature above T_eff by trapping outgoing longwave (infrared) radiation.  
- Anthropogenic emissions (CO2, CH4, etc.) increase radiative forcing, shifting the balance and causing warming.  
- Water vapor is a powerful greenhouse gas but primarily acts as a feedback that amplifies warming rather than a primary forcing.

2) Step-by-step reasoning and calculation
- Compute the average incoming absorbed solar flux: F = S(1 − A)/4 = 1361 × 0.7 / 4 ≈ 238.2 W/m².  
- Use Stefan–Boltzmann law to find T_eff: T_eff = (F/σ)^(1/4) where σ = 5.67×10^−8 W m^−2 K^−4.  
- T_eff ≈ (238.2 / 5.67e−8)^(1/4) ≈ 255 K (about −18 °C).  
- Observed global mean surface temperature ≈ 288 K (≈ +15 °C). The difference (~33 °C) is due to the natural greenhouse effect.  
- Adding CO2 and other greenhouse gases increases the atmosphere’s opacity to infrared, reducing outgoing longwave radiation until the surface and atmosphere warm to restore balance — that anthropogenic amplification is the core climate concern.

3) Why the correct answer is correct
- Option b correctly identifies that human-driven increases in greenhouse-active gases amplify the natural greenhouse effect and drive long-term climate change through radiative forcing and feedbacks.

4) Why other options are incorrect
- a: The atmosphere is not primarily heated “from space”; solar radiation heats the surface, which then emits infrared that the atmosphere absorbs.  
- c: Water vapor is indeed a greenhouse gas; it is a feedback that amplifies warming, not an absence of concern.  
- d: Greenhouse gases absorb terrestrial (infrared) radiation, not by converting visible light directly into heat.  
- e: The natural greenhouse effect is essential for a habitable climate; the problem is its anthropogenic strengthening, not the natural effect itself.

5) Conclusion
Final answer confirmed: b. The anthropogenic amplification of the natural greenhouse effect, due to increased greenhouse-active gases like CO2, is the main climate concern.

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

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