The Greenhouse Effect

The greenhouse effect refers to the changes in temperature of a planet or moon as a result of gases within the atmosphere. The change occurs due to the presence of a gas that absorbs and emits infrared radiation. William Herschel discovered infrared radiation in the early 1800s.

Herschel made the discovery by passing sunlight through a prism while holding a thermometer just beyond the end of the prism. He was surprised to find that instead of measuring room temperature, the thermometer displayed a higher temperature. He concluded that there must be an invisible form of light that was causing the temperature to rise; only it could not be seen by the naked eye.

Water vapour, carbon dioxide and methane are greenhouse gases that warm the atmosphere by absorbing thermal infrared radiation emitted by the Earth's surface, by clouds, and by the atmosphere itself. Due to this warmth, the atmosphere radiates thermal infrared in all directions and that includes back toward Earth's surface.

The notion of the greenhouse effect was discovered by Joseph Fourier. He was the first to describe the phenomenon of trapped gases in the atmosphere increasing the surface temperature of the Earth. The earliest of his published papers was completed in 1824 and then his further findings were reported in a second paper three years later.

Fourier's research established the concept of a planetary energy balance, that is, that planets acquire energy from a number of sources which lead to temperature increases. Although Fourier understood that the rate of infrared radiation increased with temperature, the exact formula for this occurrence was discovered some fifty years later and is referred to as the Stefan-Boltzmann law.

Put simply, the natural greenhouse effect is a phenomenon produced by the heat energy radiated by the sun and greenhouse gases commonly present in the atmosphere. Sunlight passes through the atmosphere and warms the Earth. The Earth then radiates this energy back towards space.

Then two things happen to the gas, either, it passes through the atmosphere and greenhouse gases (water vapour, carbon dioxide, methane and nitrous oxide) absorb part of the energy, or the remainder escapes into space. This means that some of the sun's energy becomes trapped, making the lower part of the atmosphere, and Earth, warmer. Other areas of our solar system that also display greenhouse effects according to their respective environments are, Mars, Venus and Saturn's largest moon, Titan.