What is Greenhouse Effect ?

The greenhouse effect is the process in which the absorption of infrared radiation by an atmosphere warms a planet. Without these greenhouse gases, the Earth's surface would be up to 30 °C cooler. The name comes from an incorrect analogy with the way in which greenhouses are heated by the sun in order to facilitate plant growth. In addition to the Earth, Mars, Venus and other celestial bodies with atmospheres (such as Titan) have greenhouse effects. see more details here : http://en.wikipedia.org/wiki/Green_house_effect

The greenhouse effect, first discovered by Joseph Fourier in 1824, and first investigated quantitatively by Svante Arrhenius in 1896, is the process in which the absorption of infrared radiation by an atmosphere warms a planet. Without these greenhouse gases, the Earth's surface would be up to 30 °C cooler. The name comes from an incorrect analogy with the way in which greenhouses are heated by the sun in order to facilitate plant growth. In addition to the Earth, Mars, Venus and other celestial bodies with atmospheres (such as Titan) have greenhouse effects. In common parlance, the term "greenhouse effect" may be used to refer either to the natural greenhouse effect, due to naturally occurring greenhouse gases, or to the enhanced (anthropogenic) greenhouse effect, which results from gases emitted as a result of human activities (see also global warming, scientific opinion on climate change and attribution of recent climate change).

well, he said it so...now let me tell u in an easier way... i think u must have observed the inside of ur car getting hotter if it is kept in the sun with all the windows and doors closed. it is because of the special effect of the glass which allows the sun's heat to come in but do not let out...green house is a glass house used mainly for growing plants especially in cold climates, they maintain the temperature warm inside for the plants to grow... now all planets other than earth have very wide temp. fluctuations, and without the green house gases like co2, methane etc, the Earth would also have been like them...these gases trap the light rays reflecting from the earth's atmosphere and hold them keeping the earth's atmosphere warm...this is how all the living things are able to live...but if the amount of the gases go up, then, again there will be imbalance in the temp. maintanence, and the temp. rises, this will surmount to yet another problem, called global warming...