Greenhouse Effect

The Greenhouse Effect is the process whereby short-wave radiation passes through the earth's atmosphere to surface areas. The outgoing longer-wave radiation is absorbed and reradiated by a variety of greenhouse gases, thus retaining heat in the atmosphere.

The Greenhouse Effect is a natural process in which heat from the sun is held by the Earth's atmosphere near the Earth's surface, providing enough warmth to support life. Without this effect, it is estimated that the average temperature of the Earth would be about - 18°C, the temperature of a Russian winter, and unsuitable for life. The current temperature is about 15°C.

Mars, Venus and other celestial bodies with atmospheres have greenhouse effects Mars and Venus either have too much greenhouse effect or too little to be able to sustain life as we understand it. The differences between the three planets have been termed the "Goldilocks Principle": Venus is too hot, Mars is too cold, but Earth is just right.

The Greenhouse Effect was identified by Joseph Fourier in 1824 and first investigated by Svante Arrhenius in 1896. He observed that when the industrial revolution began, more carbon dioxide was being released into the atmosphere. He was the first to understand that this increase meant a rise in the temperature of the earth.

The process known as the Greenhouse Effect works in the following way. As energy from the Sun passes through the atmosphere a number of things take place

• Some of the energy is reflected back to space by clouds and other atmospheric particles.
• A portion of the energy is absorbed by clouds, gases, and particles in the atmosphere.
• Of the remaining solar energy passing through the Earth's atmosphere, a little is reflected from the surface back to space.

On average, about 50% of the Sun's radiation reaches the surface. This energy is then used in a number of processes, including the heating of the ground surface; the melting of ice and snow and the evaporation of water; and plant photosynthesis.

Infrared radiation is emitted by the Earth's surface. As it moves up through the layers of the atmosphere, the molecules of carbon dioxide, water vapour or some other greenhouse gas in each layer absorb some of the energy.

Some of the absorbed energy is radiated back toward the ground, and some upwards to higher layers. Eventually, the energy reaches a layer so thin that radiation can escape into space.

Next: Sources of Greenhouse Gases