Role of atmospheric CO2 in the greenhouse effect Which statements correctly describe how increased atmospheric CO2 influences Earth’s energy balance?

Introduction / Context:
Greenhouse gases such as carbon dioxide change the way Earth absorbs and emits radiation. A clear understanding of shortwave versus longwave interactions explains why adding CO2 warms the surface and lower atmosphere. This question tests core radiative concepts used in climate and environmental engineering analyses.

Given Data / Assumptions:

• Sunlight reaching Earth spans mainly visible and near-infrared wavelengths (shortwave) at the top of the atmosphere.
• Earth’s surface and atmosphere emit primarily in the thermal infrared (longwave).
• CO2 has absorption bands in the infrared region.

Concept / Approach:
Shortwave solar radiation passes largely through the atmosphere to the surface, where it is absorbed and converted to heat. The warmed surface emits longwave infrared radiation upward. CO2 and other greenhouse gases interact with portions of this longwave radiation, absorbing and re-emitting it in all directions, including back toward the surface. The result is a reduction in the net rate of heat loss to space, leading to a higher equilibrium surface temperature compared with a CO2-free atmosphere.

Step-by-Step Solution:

Verification / Alternative check:
Radiative transfer models and spectral measurements show strong CO2 absorption near 15 micrometres; increases in concentration raise effective radiating height and reduce outgoing longwave radiation until temperatures adjust.

Why Other Options Are Wrong:

• Each single statement (a, b, or c) captures only part of the mechanism; the complete description requires all three.
• None of these: Incorrect because all statements collectively are consistent with greenhouse theory.

Common Pitfalls:
Confusing “visible” and “ultraviolet”; in common usage shortwave includes visible and some near-UV. The key idea is that shortwave largely passes, while longwave is partially trapped by CO2.

Final Answer:
All (a), (b) and (c)