The atmosphere is largely transparent to incoming shortwave solar radiation but acts as an efficient absorber of longwave terrestrial radiation, making surface re-emission the primary driver of atmospheric warming.
Incoming solar radiation is predominantly shortwave (visible and ultraviolet). The atmosphere absorbs only a small fraction of this directly; most passes through to heat the Earth's surface. This makes direct solar absorption a minor contributor to atmospheric temperature.
The Earth's surface, once heated, re-emits energy as longwave infrared radiation. Greenhouse gases — carbon dioxide, water vapour, methane, and nitrous oxide — absorb this longwave radiation efficiently and re-radiate it in all directions, warming the lower atmosphere. This process, not direct solar absorption, is the dominant mechanism of atmospheric heating.
Greenhouse gases possess molecular structures that resonate with longwave infrared wavelengths, enabling strong absorption. Carbon dioxide, though present in relatively small concentrations, contributes significantly to this absorption band, explaining why anthropogenic CO₂ emissions intensify the greenhouse effect and drive surface temperature rise.
Understanding that terrestrial radiation drives atmospheric heating underpins climate mitigation logic: reducing greenhouse gas concentrations directly limits longwave absorption and re-radiation. India's National Action Plan on Climate Change and international frameworks such as the Paris Agreement are grounded in this atmospheric physics.
Statement-I is incorrect — terrestrial radiation, not solar radiation, primarily heats the atmosphere — while Statement-II is correct. Accurate understanding of this mechanism is foundational to credible climate policy and emission-reduction commitments.
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