ABSTRACT
The greenhouse effect is a natural process that maintains the mean surface temperature of the globe approximately 33°C warmer than it would otherwise be, at 18°C. Without the greenhouse effect, the earth’s surface temperature would be –15°C and inhospitable to life. The principle that gases in the atmosphere trap the sun’s heat is well understood and was first elucidated by Svante Arrhenius in 1896.1
All objects emit electromagnetic radiation, with the wavelength of the radiation dependent on the temperature of the object. Hot objects (such as the filament in an incandescent light) emit short-wave radiation, and cooler objects (such as the earth) emit longer-wave radiation. The sun’s electromagnetic radiation covers a broad spectrum, from the very short wavelengths of gamma and x-rays (less than one nanometer – 10-9 m, or one millionth of a millimeter) to the very long wavelengths of microwaves (0.1-100 mm) and radio waves (100 mm to tens of meters).2 Visible light comprises a small fraction of the total radiation spectrum and covers the range of wavelengths from approximately 400-800 nanometers. The longest visible wavelength is red and the shortest is violet, and the spectra on either side of visible light are hence known as ultraviolet (UV – shorter wavelengths from 1 to 400 nanometers) and infrared (IR – longer wavelengths ranging from 800 nanometers to 0.1 mm).
