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

Question

BlackTom AI · Accepted Answer

Earth’s latitudinal temperature gradient is governed mainly by the angle and duration of incoming sunlight (insolation), not by any appreciable difference in distance to the Sun caused by Earth’s shape.

1) Relevant concepts
- Solar flux at Earth falls off as 1/r^2 (r = distance to Sun).  
- Insolation on a surface also scales with the cosine of the solar zenith angle: incoming energy per unit horizontal area = solar constant × cos(θ).  
- Earth’s oblate shape yields an equatorial bulge of only ~21 km relative to the polar radius; orbital eccentricity causes a ~3.3% seasonal variation in solar constant, but latitudinal differences come from incidence angle and day length.  
- The atmospheric greenhouse effect: shortwave (visible) passes relatively unimpeded; longwave (infrared) emitted by Earth is absorbed by greenhouse gases (H2O, CO2, etc.). Water vapor is the largest greenhouse gas by amount, but its atmospheric abundance is controlled mainly by temperature (a feedback), while humans directly emit CO2.

2) Step-by-step reasoning and calculations
- Equatorial vs polar radius difference ≈ 21 km. Distance to Sun ≈ 1.5×10^8 km. Fractional distance change ≈ 21 / 1.5×10^8 ≈ 1.4×10^-7. Flux change ≈ ~2×1.4×10^-7 ≈ 2.8×10^-7 (using 1/r^2), essentially zero.  
- By contrast, at high latitudes the solar zenith angle is large. Example: if the sun’s rays strike at 60° from vertical, cos(60°)=0.5, so a surface receives only half the energy per unit area compared to overhead sun. This cos(θ) effect and varying day length explain why tropics are warmer than poles.

3) Why the identified statement is false
- The statement “The tropics are warmer than the poles because the tropics are closer to the Sun because of the Earth’s shape…” attributes latitudinal temperature differences to an effectively zero geometrical distance effect; this is incorrect. The real cause is incidence angle and day length.

4) Why the other options are correct (briefly)
- Option 1: True — greenhouse gases transmit shortwave solar but absorb longwave terrestrial radiation.  
- Option 3: True — water vapor is the dominant greenhouse gas by amount, but humans mainly change CO2; water vapor is a feedback.  
- Option 4: True — physical greenhouses reduce convective heat loss; atmospheric greenhouse warming arises from radiative absorption by gases.  
- Option 5: True in practice — much of the warmth you feel (especially in shade or from surroundings) is infrared emitted by heated surfaces; direct sunlight is not the only source.

5) Conclusion
The false statement is: "The tropics are warmer than the poles because the tropics are closer to the Sun because of the Earth’s shape, so they receive more solar energy." This matches the provided answer.

Which of the following statements concerning greenhouse warming or climate change is FALSE?单项选择题

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