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The temperature of the surface of the Earth is mostly influenced by energy from the sun. As the sun's rays reach the Earth they are partly absorbed and partly reflected by the atmosphere before being partly absorbed and partly reflected by the surface of the Earth. This " insolation", or incident solar radiation not only gives us warmth but also creates our weather patterns. For example, it causes the evaporation of water from lakes, seas and oceans, which ultimately returns to Earth as rain, sleet or snow; it heats some parts of the surface more quickly than others and this produces pressure differentials which result in wind. The spinning of the Earth usually means that winds circle as anticyclones in the Northern Hemisphere and as Cyclones in the Southern Hemisphere.
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The atmosphere effectively insulates the Earth by preventing all of the heat from escaping out into space. You may have noticed how quickly the temperature drops on cloudless nights. This is because clouds help to insulate the Earth, but here we are concerned with the average temperature of the Earth, which is maintained by the insulating properties of the atmosphere. Put technically, the atmosphere is relatively good at transmitting visible light and the more energetic violet and ultraviolet radiation from the sun. We therefore enjoy daylight and warmth. The atmosphere is a poor transmitter of the red and infrared radiation, which is the predominant radiation from the Earth. The sun being hot radiates in the energetic part of the spectrum, whereas the Earth is much cooler and so radiates to the infrared. Without the atmosphere the Earth's IR radiation would escape into space and the Earth would be much cooler: probably too cold to support life. The atmosphere acts in exactly the same way as greenhouse glass, hence the term the 'Greenhouse Effect'. The Greenhouse Effect is essential to our life. The stratosphere, which is the main part of the atmosphere containing the gases that create this greenhouse effect, is 10-50km above the surface of the Earth.
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