CBSE Class 11-science Answered

This is because they absorb infra red radiations and do not allow the radiations to move through the atmosphere. The IR rays are trapped by the green house gases and cause the ehating of earth's atmosphere.

Solar radiation from the sun passes through Earth's atmosphere, then is absorbed by the surface of the Earth, causing it to warm.  Part of the absorbed energy is then reradiated back to the atmosphere as infared radiation.  Little of this infra red radiation escapes back into space. These radiations cannot pass through the greenhouse gases in the atmosphere. The greenhouse gases selectively transmit the infared waves, trapping some and allowing some to pass through into space. The greenhouse gases absorb these waves and reemits the waves downward, causing the lower atmosphere to warm.