Previous Year Question

The Earth receives energy from the Sun mainly in the form of short-wave solar radiation. The atmosphere is relatively transparent to a large part of this incoming short-wave radiation, so a substantial proportion reaches the Earth's surface and heats the land and oceans.

The heated Earth's surface then emits energy, but unlike incoming solar radiation, this energy is emitted mainly in the form of long-wave infrared radiation. This is known as Terrestrial Radiation.

Water vapour, carbon dioxide and other greenhouse gases present in the atmosphere efficiently absorb this long-wave radiation. Therefore, rather than being heated primarily by direct solar radiation, the atmosphere is mainly heated from below by terrestrial radiation emitted from the Earth's surface.

This is also one reason why temperature generally decreases with increasing altitude in the troposphere. The standard environmental lapse rate is taken as about 6.5°C per 1,000 metres, although the actual rate varies with place and time.