Greenhouse Effect The greenhouse effect is a natural phenomenon that warms the earth and enables it to support life. Without it, the average temperature on earth would be around -18 degrees C, instead of the current +15 degrees C - a frozen wilderness. It works on the same principles as the ordinary glass garden greenhouse, where glass allows light to get in, but does not allow for the heat to get out. This makes for a much higher temperature inside the greenhouse. On a planetary scale, similar processes occur. Light from the sun has no trouble penetrating the atmosphere and reaching the earth's surface, warming it.