UGC NET Questions (Paper – 1)

The natural greenhouse effect arises from gases like water vapour and carbon dioxide that trap some outgoing longwave radiation. Without this natural insulation, the Earth's average surface temperature would be far below freezing. By keeping the planet warm enough for liquid water, the greenhouse effect makes life possible. Therefore, Option A, which states that it keeps temperature at a level suitable for life, is correct.

Option A:
Option A correctly summarises the beneficial role of the natural greenhouse effect. It highlights that, without this natural warming, Earth would be too cold to support the forms of life we know.

Option B:
Option B is incorrect because the greenhouse effect warms the Earth instead of freezing it. Removing greenhouse gases, not having them, would push the planet towards a much colder state.

Option C:
Option C is incorrect since the greenhouse effect does not block incoming solar radiation. Sunlight still reaches the surface; greenhouse gases mainly reduce the loss of outgoing infrared (heat) radiation.

Option D:
Option D is incorrect because greenhouse gases and the associated effect have existed since long before human industrial activity. Humans have only enhanced this natural effect in the last two centuries.