Greenhouse gases like carbon dioxide trap heat in Earth’s atmosphere by absorbing and re-emitting infrared radiation.

Question Breakdown

This GATE Life Sciences question evaluates understanding of the greenhouse effect mechanism. Greenhouse gases (CO₂, CH₄, N₂O) allow shortwave solar radiation to pass through but absorb outgoing longwave infrared heat from Earth’s surface, warming the planet.​

Option Analysis

(A) Destroying ozone in the stratosphere

CFCs deplete stratospheric ozone, but CO₂ and other greenhouse gases do not; ozone itself is a greenhouse gas.​

(B) Trapping heat in the earth’s atmosphere

Correct. Gases absorb infrared radiation emitted by Earth, re-radiating it in all directions (including downward), retaining heat like a blanket.

(C) Allowing more visible light to reach the earth’s surface

Greenhouse gases are transparent to visible light (0.4-0.7 μm), allowing it to reach the surface; they block infrared.​

(D) Reducing the amount of radiant energy which reaches the surface of the earth

Opposite effect: they permit incoming solar radiation while trapping outgoing heat.​

Greenhouse gases trapping heat earth atmosphere causes global warming through the natural greenhouse effect, intensified by human emissions.​

Greenhouse Effect Mechanism

Sunlight passes through the atmosphere to warm Earth’s surface, which emits infrared radiation. Greenhouse gases absorb this IR and re-emit it, trapping ~90% of heat. Without this, Earth would be ~33°C colder.

Comparison Table

GATE Exam Relevance

Tests environmental science basics in XL papers. Key: distinguish greenhouse effect from ozone depletion. Study radiative forcing for climate questions.​