The temperature on earth’s surface is determined by the solar radiation energy and heat reflected from the earth to outer space. Sunlight warms the surface, and then emits energy in the form infrared rays, or heat. Then a certain percentage of these rays are absorbed in the by atmospheric gases, thus heating the atmosphere which in turn radiates heat back toward earth’s surface. With this process, known as the “greenhouse effect”, the earth’s average surface temperature is kept around 15 C. If not for this process the temperature of the earth would drop by over 30C to about -18C, making it nearly unsuitable for us to survive.