absorbed by land, oceans, and vegetation, and transformed to heat, which is reradiated as invisible infrared radiation (The Greenhouse). However, the Earth's atmosphere contains molecules which absorb the heat and reradiate it in all directions, reducing the heat radiated back into space. These molecules are called greenhouse gases because they hold the heat in. Carbon dioxide molecules can absorb infrared radiation, which causes them to vibrate and readmit the radiation, to be absorbed by another molecule. This keeps the heat trapped near the Earth's surface. Other molecules such as water vapor, methane and nitrous oxide behave in the same way. They are all composed of at least two atoms bound together loosely enough to allow vibration and the absorption and emission of radiation. Nitrogen (N2) and oxygen (02), the major components of the atmosphere, have molecules bound tightly together and so they do not absorb radiation and are not greenhouse gases.
In the '50s, greenhouse gases became associated with climate change, and more recently there has been concern about an enhanced greenhouse gas effect (The Greenhouse). The atmospheric greenhouse effect is affected by the type of surface on which the solar energy falls, more being reflected back into space from a white surface such as a polar ice cap than from a dark surface such as a desert. Clouds also affect the amount of solar radiation reaching the Earth and block the radiation of the infrared energy back into space.
Temperatures are increasing slowly across the world (Will). The average surface temperature has increased 0.4 degrees Celsius (plus or minus 0.1 degree) in the past 25 years. By the year 2100, the World Meteorological Organization has estimated the global surface temperature may rise by between 1.4 and 5.8 degrees Celsius. The actual value depends on whether or not the atmosphere becomes more humid as warming occurs. If it does, the warming will b...